CIE IGCSE Physics Revision Notes PDF

CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ CONTENTS 1.1 Length & Time 1.1....

CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ CONTENTS 1.1 Length & Time 1.1.1 Measurement 1.2 Motion 1.2.1 Speed & Acceleration 1.2.2 Distance-Time Graphs 1.2.3 Velocity-Time Graphs 1.2.4 Freefall 1.3 Mass & Weight 1.3.1 Mass & Weight 1.4 Density 1.4.1 Density 1.5 Forces 1.5.1 Change of Shape 1.5.2 Balanced Forces 1.5.3 Unbalanced Forces 1.5.4 Circular Motion 1.5.5 Turning Effect 1.5.6 Conditions For Equilibrium 1.5.7 Centre of Mass 1.5.8 Scalars & Vectors 1.6 Momentum 1.6.1 Momentum 1.7 Energy, Work & Power 1.7.1 Energy 1.7.2 KE & GPE 1.7.3 Energy Resources 1.7.4 Efficiency 1.7.5 Work 1.7.6 Power 1.8 Pressure 1.8.1 Pressure © copyright Save My Exams CIE IGCSE Physics Resources Page 1 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.1 LENGTH & TIME 1.1.1 MEASUREMENT Distance & Volume Rulers can be used to measure small distances of a few cm. They are able to measure to the nearest mm A ruler can measure small distances to the nearest mm When measuring larger distances (of a few metres) a tape measure is more appropriate or, when measuring even larger distances, a trundle wheel © copyright Save My Exams CIE IGCSE Physics Resources Page 2 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Trundle wheels can be used to measure large distances © copyright Save My Exams CIE IGCSE Physics Resources Page 3 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Measuring cylinders can be used to measure the volume of liquids or, by measuring the change in volume, the volume of an irregular shape Measuring cylinders can be used to determine the volume of a liquid or an irregular shaped solid © copyright Save My Exams CIE IGCSE Physics Resources Page 4 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Micrometer Screw Gauge When measuring very small distances (less than a centimetre) a micrometer is the most appropriate instrument Micrometers can be used to measure very small distances Micrometers can measure distances to the nearest 1/100th of a mm © copyright Save My Exams CIE IGCSE Physics Resources Page 5 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Time Stop-clocks and stopwatches can be used to measure time intervals An important factor when measuring time intervals is human reaction time. This can have a significant impact upon measurements when the measurements involved are very short (less than a second) Multiple Readings Suppose you have to measure the thickness of a sheet of paper. The thing that you are trying to measure is so small that it would be very difficult to get an accurate answer If, however, you measure the thickness of 100 sheets of paper you can do so much more accurately. Dividing your answer by 100 will then give an accurate figure for the thickness of one sheet This process of taking a reading of a large number of values and then dividing by the number, is a good way of getting accurate values for small figures, including (for example) the time period of a pendulum – measure the time taken for 10 swings and then divide that time by 10 Exam Question: Easy © copyright Save My Exams CIE IGCSE Physics Resources Page 6 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Medium © copyright Save My Exams CIE IGCSE Physics Resources Page 7 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 8 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.2 MOTION 1.2.1 SPEED & ACCELERATION Speed Speed (measured in metres per second) is the distance moved by an object each second The average speed of an object is given by the equation: © copyright Save My Exams CIE IGCSE Physics Resources Page 9 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ You can rearrange the equation with the help of the formula triangle: Use the formula triangle to help you rearrange the equation Exam Tip Use the units of speed (metres per second – distance divided by time) to help you remember the formula The equation is for average speed, but the speed at a specific moment might be higher or lower © copyright Save My Exams CIE IGCSE Physics Resources Page 10 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Velocity Velocity is a similar quantity to speed, but includes a direction (the direction of travel) as well as its value (its magnitude) Two objects can have equal speeds but might have opposite velocities (if they are travelling in opposite directions) The two cars have the same speed but opposite velocities, because they are travelling in opposite directions © copyright Save My Exams CIE IGCSE Physics Resources Page 11 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Acceleration Acceleration is the rate of change of velocity: In other words, how much the velocity of an object changes by every second Acceleration is given by the equation: (Where u is the initial velocity of an object and v is its final velocity) You can rearrange this equation with the help of the formula triangle: © copyright Save My Exams CIE IGCSE Physics Resources Page 12 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Use the formula triangle to help you rearrange the equation The units of acceleration are m/s2, which mean the same thing as m/s/s – the change in velocity (in m/s) every second Exam Tip Marks are often available for giving the correct unit, even if your answer is incorrect. You must, however, give an answer (even if it’s just a guess): giving a unit without an answer will not gain you any marks. © copyright Save My Exams CIE IGCSE Physics Resources Page 13 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.2.2 DISTANCE-TIME GRAPHS Distance-Time Graphs: Basics A distance-time graph shows how the distance of an object (from a point) varies over time: Graphs showing how the distances travelled by three objects vary over time A horizontal line means stationary A straight line means constant speed If the gradient increases the object is speeding up (accelerating) If the gradient decreases the object is slowing down (decelerating) If the line is going down, the object is moving backwards © copyright Save My Exams CIE IGCSE Physics Resources Page 14 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Calculating Speed The speed of an object is given by the gradient of the line © copyright Save My Exams CIE IGCSE Physics Resources Page 15 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.2.3 VELOCITY-TIME GRAPHS Velocity-Time Graphs: Basics A Velocity-time graph shows how the velocity (or speed) of an object changes over time Graph showing how the velocity (speed) of an object changes over time If the line is horizontal, the velocity is constant (no acceleration) If the line slopes upwards then the object is accelerating (speeding up) If the line goes down then the object is decelerating (slowing down) © copyright Save My Exams CIE IGCSE Physics Resources Page 16 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Calculating Distance The distance travelled by an object can be found by determining the area beneath the graph The distance travelled can be found from the area beneath the graph If the area beneath the graph forms a triangle (the object is accelerating or decelerating) then the area can be determined using the formula: If the area beneath the graph is a rectangle (constant velocity) then the area can be determined using the formula: area = ½ x base x height If the area beneath the graph is a rectangle (constant velocity) then the area can be determined using the formula: area = base x height © copyright Save My Exams CIE IGCSE Physics Resources Page 17 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip When asked to find the distance, start by stating: distance = area beneath graph A common mistake is to try and find distance using the distance-speed-time equation. This equation will not work if the speed of the object is changing. © copyright Save My Exams CIE IGCSE Physics Resources Page 18 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Calculating Acceleration The acceleration of an object is given by the gradient of the graph: Graph showing how acceleration can be determined from gradient Lines that slope downwards have negative gradients and so can be said to have negative accelerations: This is the same thing as a deceleration If the gradient of the line changes then the acceleration of the body must be changing: A line with constant gradient represents constant acceleration (linear motion) A curved line represents changing acceleration – either decreasing (if the gradient gets smaller) or increasing (if the gradient gets large) © copyright Save My Exams CIE IGCSE Physics Resources Page 19 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip Remember to include units when giving your answers. The units of acceleration, for example, are m/s2 © copyright Save My Exams CIE IGCSE Physics Resources Page 20 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.2.4 FREEFALL Freefall: Basics In the absence of air resistance, all objects fall with the same acceleration, regardless of their mass This acceleration is equal to the gravitational field strength and is approximately 10 m/s2 near the Earth’s surface So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for. In the absence of air resistance objects fall with constant acceleration © copyright Save My Exams CIE IGCSE Physics Resources Page 21 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Terminal Velocity When a parachutist jumps out of an aeroplane, two main forces act: Weight (the force of gravity) Air resistance Diagram showing how the changing forces on a skydiver © copyright Save My Exams CIE IGCSE Physics Resources Page 22 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Initially the air resistance is very small. There is a downwards unbalanced force and the skydiver accelerates As the skydiver speeds up, the air resistance increases Eventually the air resistance balances the weight and so the skydiver travels at a constant speed – terminal velocity When the parachute is opened the increase air resistance on the parachute creates an upwards unbalanced force, making the parachuting the slow down Graph showing how the velocity of a skydiver changes during the descent © copyright Save My Exams CIE IGCSE Physics Resources Page 23 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip The force of gravity on an object is called weight. If asked to name this force make sure you use this word: Don’t refer to it as “gravity” as this term could also mean gravitational field strength and so would probably be marked wrong. Likewise, refer to the upward force as air resistance or drag. The terms wind resistance and air pressure mean different things and so would also be marked wrong. © copyright Save My Exams CIE IGCSE Physics Resources Page 24 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Easy © copyright Save My Exams CIE IGCSE Physics Resources Page 25 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Medium © copyright Save My Exams CIE IGCSE Physics Resources Page 26 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 27 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.3 MASS & WEIGHT 1.3.1 MASS & WEIGHT Mass & Weight: Basics Mass (measured in kilograms, kg) is related to the amount of matter in an object Weight (measured in newtons, N) is the force of gravity on a mass The size of this force depends on the gravitational field strength (often called gravity, g, for short) weight = mass x gravitational field strength W = m x g You can rearrange this equation with the help of the formula triangle: © copyright Save My Exams CIE IGCSE Physics Resources Page 28 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Use the formula triangle to help you rearrange the equation The value of g (the gravitational field strength) varies from planet to planet On Earth: Diagram showing the gravitational field strengths of the planets in our solar system The weight (and hence mass) of two objects can be compared using a balance A balance can be used to compare two different weights © copyright Save My Exams CIE IGCSE Physics Resources Page 29 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip Mass is usually measured in kilograms in Physics. If it is given in grams, you might need to convert to kilograms by dividing the mass by 1000 It is easy to confuse mass and weight. – take care to use each term appropriately When referring to the force of gravity: ⚬ be careful to call it weight, gravitational force or gravitational attraction ⚬ Don’t refer to it as just gravity and certainly don’t call it gravitational field strength or gravitational potential (both of which mean different things) © copyright Save My Exams CIE IGCSE Physics Resources Page 30 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only The Significance of Mass Mass has two significant effects in Physics: The mass of an object’s opposed any attempt to change that object’s motion The greater the mass of an object, the more difficult it is to speed it up, slow it down or change its direction This property of mass is sometimes referred to as inertia Mass is also the source of an object’s weight – the force of gravity on a mass The greater the mass, the greater the weight Exam Question: Easy © copyright Save My Exams CIE IGCSE Physics Resources Page 31 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 32 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.4 DENSITY 1.4.1 DENSITY Density: Basics Density is the mass per unit volume of a material: Objects made from low-density materials typically have a low mass, whilst similar- sized objects made from high-density materials have a high mass (Think of how heavy a bag full of feathers is compared to a similar bag full of metal) Density is related to mass and volume by the following equation: (Note: The greek letter ρ is used to mean density) © copyright Save My Exams CIE IGCSE Physics Resources Page 33 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ You can rearrange this equation with the help of the formula triangle: Use the formula triangle to help you rearrange the equation The units of density depend on what units are used for mass and volume: If the mass is measured in g and volume in cm3, then the density will be in g/cm3 If the mass is measured in kg and volume in m3, then the density will be in kg/m3 © copyright Save My Exams CIE IGCSE Physics Resources Page 34 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip The main thing to remember is that density is mass per unit volume In Physics, mass is almost always measured in kg Density is the only topic in which physicists sometimes use grams instead © copyright Save My Exams CIE IGCSE Physics Resources Page 35 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Floating In general, an object will float in a liquid if the average density of that object is less than the density of the liquid it is placed in Water, for example, has a density of about 1 g/cm3 If an object has a density of less than 1 g/cm3 then it will float in water If an object has a density that is greater than 1 g/cm3 then it will sink in water Diagram showing the relationship between an object’s density and its ability to float in water © copyright Save My Exams CIE IGCSE Physics Resources Page 36 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Measuring Density To measure the density of an object, we must measure its mass and volume and then use the following equation: The mass of an object can be measured quite simply by placing it on a top pan balance You ought to state that you will ‘zero’ the balance before using it Always zero a top pan balance before taking any measurements In the case of a liquid, the liquid must be placed in a container, the mass of which should be measured both when it is empty and when it contains the liquid: The mass of the liquid will be the difference between the two values © copyright Save My Exams CIE IGCSE Physics Resources Page 37 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ The volume can be determined in a couple of ways: Regular shapes (e.g. cubes, spheres, cylinders): The width (and length) can be measured using a ruler or a pair of digital calipers To make the measurements accurate, several measurements should be taken between different faces or points on the circumference, and an average taken When measuring the width (or diameter) take several readings between different points and take an average The volume can then be calculated using an appropriate equation: © copyright Save My Exams CIE IGCSE Physics Resources Page 38 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ (Note: When measuring the width of a sphere or cylinder, divide the measurement by two to find the radius) Irregular shapes: The volume can be found using a Eureka can: Placing an object in a full Eureka can will displace water equal to its volume Fill the Eureka can with water Place an empty measuring cylinder below its spout © copyright Save My Exams CIE IGCSE Physics Resources Page 39 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Now carefully lower the object into the Eureka can (use a piece of string, perhaps) Measure the volume of displaced water in the measuring cylinder Alternatively, the object can be placed in a measuring cylinder containing a known volume of liquid, and the change in volume then measured When an irregular solid is placed in a measuring cylinder, the level of the liquid will rise by an amount equal to the volume of the solid Once the mass and volume of the shape is known, its density can be calculated © copyright Save My Exams CIE IGCSE Physics Resources Page 40 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 41 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5 FORCES 1.5.1 CHANGE OF SHAPE © copyright Save My Exams CIE IGCSE Physics Resources Page 42 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Stretching Materials When forces are applied to materials, the size and shape of the material can change The method below describes a typical procedure for carrying out an investigation into the properties of a material An experiment to measure the extension of a spring Set up the apparatus as shown in the diagram A single mass (0.1 kg, 100g) is attached to the spring, with a pointer attached to the bottom, and the position of the spring is measured against the ruler The mass (in kg) and position (in cm) are recorded in a table A further mass is added and the new position measured The above process continues until a total of 7 masses have been added The masses are then removed and the entire process repeated again, until it has been carried out a total of three times, and averages can then be taken © copyright Save My Exams CIE IGCSE Physics Resources Page 43 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Once measurements have been taken: The force on the spring can be found by multiplying the mass on the spring (in kg) by 10 N/kg (the gravitational field strength) The extension of the spring can be found by subtracting the original position of the spring from each of the subsequent positions Finally, a graph of extension (on the y-axis) against force (on the x-axis) should be plotted A graph of force against extension for a metal spring © copyright Save My Exams CIE IGCSE Physics Resources Page 44 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Hooke's Law Hooke’s law states that: The extension of a spring is proportional to the applied force (where k is the spring constant, which represents how stiff a spring is) Many other materials (such as metal wires) also obey Hooke’s law Hooke’s law is associated with the initial linear (straight) part of a force-extension graph Objects that obey Hooke’s law will return to their original length after being stretched If an object continues to be stretched it can be taken past the limit of proportionality (sometimes called the elastic limit). At this point the object will no longer obey Hooke’s law and will not return to its original length © copyright Save My Exams CIE IGCSE Physics Resources Page 45 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ The spring on the right has been stretched beyond the limit of proportionality Exam Tip A relationship is said to be proportional if the graph is a straight line going through the origin. If a graph is a straight line but does not go through the origin the relationship is said to be linear. © copyright Save My Exams CIE IGCSE Physics Resources Page 46 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.2 BALANCED FORCES Resultant Force When several forces act on a body, the resultant (overall) force on the body can be found by adding together forces which act in the same direction and subtracting forces which act in opposite directions: Diagram showing the resultant forces on three different objects When the forces acting on a body are balanced (i.e. there is no resultant force), the body will either remain at rest or continue to move in a straight line at a constant speed © copyright Save My Exams CIE IGCSE Physics Resources Page 47 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ When the forces acting on a body are balanced the body will remain at rest or continue to travel at a constant speed in a straight line © copyright Save My Exams CIE IGCSE Physics Resources Page 48 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Friction Friction is a force that opposes the motion of an object caused by the contact (rubbing) of two surfaces. It always acts in the opposite direction to the direction in which the object is moving Friction opposes the motion of an object Air resistance (sometimes called drag) is a form of friction caused by a body moving through the air Friction (including air resistance) results in energy loss due to the transfer of energy from kinetic to internal (heat) © copyright Save My Exams CIE IGCSE Physics Resources Page 49 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip The resultant force is sometimes also known as the net force or the unbalanced force. Avoid referring to air resistance as wind resistance or air pressure – these are incorrect terms and will lose you marks if you use them when you actually mean air resistance. © copyright Save My Exams CIE IGCSE Physics Resources Page 50 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.3 UNBALANCED FORCES Forces & Motion When an unbalanced (resultant) force acts on an object, it can affect its motion in a number of ways: The object could speed up The object could slow down The object could change direction A resultant force can cause an object to speed up, slow down or change direction © copyright Save My Exams CIE IGCSE Physics Resources Page 51 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Acceleration Force, mass and acceleration are related by the following equation: force = mass × acceleration f = m × a You can rearrange this equation with the help of the formula triangle: Use the formula triangle to help you rearrange the equation The greater the force, the greater the acceleration (for a given mass) For a given force, the smaller the mass the greater the acceleration © copyright Save My Exams CIE IGCSE Physics Resources Page 52 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip If you are trying to find the acceleration check that you know both the unbalanced (resultant) force and the mass of the object. If you don’t, you might need to calculate the acceleration using a different equation. © copyright Save My Exams CIE IGCSE Physics Resources Page 53 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.4 CIRCULAR MOTION Extended Only Changing Direction When a force acts at 90 degrees to an object’s direction of travel, the force will cause that object to change direction When the two cars collide, the first car changes its direction in the direction of the force © copyright Save My Exams CIE IGCSE Physics Resources Page 54 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ If the force continues to act at 90 degrees to the motion, the object will keep changing its direction (whilst remaining at a constant speed) and travel in a circle This is what happens when a planet orbits a star (or satellite orbits a planet) The Moon is pulled towards the Earth (at 90 degrees to its direction of travel). This causes it to travel in a circular path The force needed to make something follow a circular path depends on a number of factors: The mass of the object (a greater mass requires a greater force) The speed of the object (a faster-moving object requires a greater force) The radius of the circle (a smaller radius requires a greater force) © copyright Save My Exams CIE IGCSE Physics Resources Page 55 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.5 TURNING EFFECT The Moment of a Force A moment is the turning effect of a force Moments occur when forces cause objects to rotate about some pivot The size of the moment depends upon: The size of the force The distance between the force and the pivot The moment of a force is given by the equation: Moment = Force × perpendicular distance from the pivot Moments have the units newton centimetres (N cm) or newton metres (N m), depending on whether the distance is measured in metres or centimetres Diagram showing the moment of a force causing a block to topple © copyright Save My Exams CIE IGCSE Physics Resources Page 56 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Some other examples involving moments include: Using a crowbar to prize open something Turning a tap on or off Opening or closing a door © copyright Save My Exams CIE IGCSE Physics Resources Page 57 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ The Principle of Moments The principle of moments states that: For a system to be balanced, the sum of clockwise moments must be equal to the sum of anticlockwise moments Diagram showing the moments acting on a balanced beam In the above diagram: Force F2 is supplying a clockwise moment; Forces F1 and F3 are supplying anticlockwise moments Hence: F2 x d2 = F1 x d1 + F3 x d3 © copyright Save My Exams CIE IGCSE Physics Resources Page 58 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Example of The Principle of Moments The principle of moments doesn’t just apply to seesaws – it is important in many other situations as well such as, for example, a shelf: To prevent the shelf from collapsing, the support must provide an upward moment equal to the downward moment of the vase © copyright Save My Exams CIE IGCSE Physics Resources Page 59 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ © copyright Save My Exams CIE IGCSE Physics Resources Page 60 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.6 CONDITIONS FOR EQUILIBRIUM Equilibrium Defined The term “equilibrium” means that an object keeps doing what it’s doing, without any change Therefore: If the object is moving it will continue to move (in a straight line) If it is stationary it will remain stationary The object will also not start or stop turning The above conditions require two things: The forces on the object must be balanced (there must be no resultant force) The sum of clockwise moments on the object must equal the sum of anticlockwise moments (the principle of moments) When the forces and moments on an object are balanced, the object will remain in equilibrium If the above two conditions are met, then the object will be in equilibrium © copyright Save My Exams CIE IGCSE Physics Resources Page 61 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Demonstrating Equilibrium A simple experiment to demonstrate that there is no net moment on an object in equilibrium involves taking an object, such as a beam, and replacing the supports with newton (force) meters: Several forces act on a supported beam, including the mass of the beam and the mass of an object suspended from it The beam in the above diagram is in equilibrium The various forces acting on the beam can be found either by taking readings from the newton meters or by measuring the masses (and hence calculating the weights) of the beam and the mass suspended from the beam The distance of each force from the end of the ruler can then be measured, allowing the moment of each force about the end of the ruler to be calculated It can then be shown that the sum of clockwise moments (due to forces F2 and F3) equal the sum of anticlockwise moments (due to forces F1 and F4) © copyright Save My Exams CIE IGCSE Physics Resources Page 62 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ © copyright Save My Exams CIE IGCSE Physics Resources Page 63 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.7 CENTRE OF MASS Finding the Centre of Mass The centre of mass of an object (sometimes called the centre of gravity) is the point through which the weight of that object acts For a symmetrical object of uniform density (such as a symmetrical cardboard shape) the centre of mass is located at the point of symmetry: The centre of mass of a regular shape can be found by symmetry © copyright Save My Exams CIE IGCSE Physics Resources Page 64 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ When an object is suspended from a point, the object will always settle so that it’s centre of mass comes to rest below the pivoting point This can be used to find the centre of mass of an irregular shape: Diagram showing an experiment to find the centre of mass of an irregular shape The irregular shape (a plane laminar) is suspended from a pivot and allowed to settle A plumb line (lead weight) is then held next to the pivot and a pencil is used to draw a vertical line from the pivot (the centre of mass must be somewhere on this line) The process is then repeated, suspending the shape from two different points The centre of mass is located at the point where all three lines cross © copyright Save My Exams CIE IGCSE Physics Resources Page 65 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Stability An object is stable when its centre of mass lies above its base The object on the right will topple, as its centre of mass is no longer over its base © copyright Save My Exams CIE IGCSE Physics Resources Page 66 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ If the centre of mass does not lie above its base, then an object will topple over The most stable objects have a low centre of mass and a wide base The most stable objects have wide bases and low centres of mass © copyright Save My Exams CIE IGCSE Physics Resources Page 67 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.5.8 SCALARS & VECTORS Extended Only Scalars & Vectors Quantities can be one of two types: A scalar or a vector Scalars are quantities that have only a magnitude (a number describing how big they are) Vectors have both magnitude and direction The cars in the above diagram have the same speed (a scalar quantity) but different velocities (a vector quantity) © copyright Save My Exams CIE IGCSE Physics Resources Page 68 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Force is a vector quantity – it has both magnitude and direction The force is represented by the arrow. Its length gives the magnitude (size) of the force and the arrow also shows its direction © copyright Save My Exams CIE IGCSE Physics Resources Page 69 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Some common scalars and vectors are given below Note: Some vector quantities (such as displacement and velocity) are very similar to some corresponding scalar quantities (distance and speed) © copyright Save My Exams CIE IGCSE Physics Resources Page 70 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Adding Vectors Vectors can be added together to produce a resultant vector. The rules for doing this, however, are slightly different to scalars: If two vectors point in the same direction, the resultant vector will also have the same directions and its value will be the result of adding the magnitudes of the two original vectors together If two vectors point in opposite directions then subtract the magnitude of one of the vectors from the other one. The direction of the resultant will be the same as the larger of the two original vectors Diagram showing the result of adding two aligned vectors (forces) together © copyright Save My Exams CIE IGCSE Physics Resources Page 71 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ If the two vectors point in completely different directions, then the value of the resultant vector can be found graphically: Draw an arrow representing the first vector Now starting at the head of the first arrow, draw a second arrow representing the second vector The resultant vector can be found by drawing an arrow going from the tail of the first vector to the tip of the second vector Diagram showing an example of the “tip-to-tail” addition of two vectors Exam Question: Medium © copyright Save My Exams CIE IGCSE Physics Resources Page 72 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 73 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.6 MOMENTUM 1.6.1 MOMENTUM Extended Only Momentum Defined Momentum is defined by the equation: momentum = mass × velocity p = m × v (where p stands for momentum) Momentum is defined as the product of mass and velocity © copyright Save My Exams CIE IGCSE Physics Resources Page 74 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ The units of momentum are kg m/s (the units of mass multiplied by the units of velocity) Momentum is a vector quantity – it has direction as well as magnitude This means that momentum can be negative as well as positive: If an object travelling to the right has positive momentum, an object travelling in the opposite direction (to the left) will have negative momentum © copyright Save My Exams CIE IGCSE Physics Resources Page 75 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only The Conservation of Momentum In the absence of external forces (such as friction), the total momentum of a system remains the same This means that in a collision, the sum of the momentums before the collision will be the same as the sum of momentums after the collision Diagram showing the total momentum of a system before and after a collision In the above diagram the total momentum before and the total momentum after must be equal: m × u = M × V - m × v Note that because the red ball is travelling to the left after the collision, its momentum will be negative – hence the minus sign in the above equation © copyright Save My Exams CIE IGCSE Physics Resources Page 76 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Impulse When a resultant (unbalanced) force acts on a mass, the momentum of that mass will change The impulse of a force is equal to that force multiplied by the time for which it acts: impulse = F × t The change in momentum of a mass is equal to the impulse provided by the force: impulse = change in momentum F × t = mv - mu (Where u is the initial velocity of the mass and v is the final velocity of the mass) Exam Question: Easy © copyright Save My Exams CIE IGCSE Physics Resources Page 77 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Medium © copyright Save My Exams CIE IGCSE Physics Resources Page 78 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Question: Hard > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK © copyright Save My Exams CIE IGCSE Physics Resources Page 79 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7 ENERGY, WORK & POWER 1.7.1 ENERGY The Conservation of Energy Energy is the capacity of something to do work: If something contains a store of energy it is able to do work If something does not store energy then it will not work The law of conservation of energy states that: Energy cannot be created or destroyed, it can only change from one form to another What this means is that the total amount of energy in a closed system remains constant, although how much of each form there is may change Some examples: A falling object (in a vacuum): Gravitational potential energy → Kinetic energy A gas cooker: Chemical → Internal (Heat) An LED (Light Emitting Diode): Electrical → Light © copyright Save My Exams CIE IGCSE Physics Resources Page 80 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Conservation of Energy in Multiple Stages Many processes involve several steps before energy ends up in its final form For example: A fossil fuel power station takes chemical energy (the fuel) and uses it to produce electrical energy, but the individual steps are: Chemical → Internal (heat) → Kinetic (steam) → Kinetic (turbine and generator) → Electrical Types of Energy Energy can exist in a number of forms For your IGCSE examination you are expected to know about the following: © copyright Save My Exams CIE IGCSE Physics Resources Page 81 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Worked example showing how energy is stored and transferred © copyright Save My Exams CIE IGCSE Physics Resources Page 82 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Energy Transfer In addition to the six forms of energy mentioned above, there are four ways in which energy can be transferred from one form to another: © copyright Save My Exams CIE IGCSE Physics Resources Page 83 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Energy Dissipation When energy is transferred from one form to another, not all of the energy will end up in the desired form (or place) This lost energy often ends up being dissipated (spreading out into the environment), usually in the form of heat, light or sound Diagram showing the forms of energy transfers and stores © copyright Save My Exams CIE IGCSE Physics Resources Page 84 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Exam Tip The classification of energy into forms and transfers, as mentioned above, is a fairly new approach and so there is a chance that you may have been taught this topic slightly differently or have come across different approaches elsewhere. Don’t worry if this is the case, but you will need to become familiar with the above classification as there is a very good chance that it will be used in your examinations. © copyright Save My Exams CIE IGCSE Physics Resources Page 85 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7.2 KE & GPE © copyright Save My Exams CIE IGCSE Physics Resources Page 86 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Gravitational Potential Energy The gravitational potential energy (GPE) of an object is the energy it has due to its height in a gravitational field: If an object is lifted up it will gain GPE If it falls, it will lose GPE Gravitational potential energy: The energy an object has when it is lifted up © copyright Save My Exams CIE IGCSE Physics Resources Page 87 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ The GPE of an object is related to its mass (m), height (h) and the gravitational field strength (g): The gravitational field strength (g) on the Earth is approximately 10 N/kg (You will always be told this value in your examination paper) © copyright Save My Exams CIE IGCSE Physics Resources Page 88 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Kinetic Energy The kinetic energy (KE) of an object is the energy it has as a result of its speed Kinetic energy: the energy an object has when it is moving It is related to the mass (m) and speed (v) of the object by the equation: (Note: In the above equation only the speed is squared – not the mass or the ½) © copyright Save My Exams CIE IGCSE Physics Resources Page 89 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Worked example showing how GPE transfers to KE © copyright Save My Exams CIE IGCSE Physics Resources Page 90 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7.3 ENERGY RESOURCES Descriptions & Forms Energy resources are large banks of energy that can be transferred into a form that can be used by society, such as electrical energy The table below gives a brief description of the main energy resources, along with the form of energy contained in that resource Advantages and Disadvantages © copyright Save My Exams CIE IGCSE Physics Resources Page 91 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ All energy resources have advantages and disadvantages associated with them © copyright Save My Exams CIE IGCSE Physics Resources Page 92 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Some points to note: A renewable energy resource is one that is replenished at a faster rate than the rate at which it is being used As a result of this, renewable energy resources cannot run out A reliable energy resource is one that can produce energy at any time Non-reliable resources can only produce energy some of the time (e.g. when it’s windy) © copyright Save My Exams CIE IGCSE Physics Resources Page 93 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only The Sun Most of our energy resources on the Earth come from the Sun: The Sun heats up the atmosphere, creating wind and producing waves Water evaporated by the Sun falls as rain, filling up reservoirs Plants grown using sunlight form the basis for fuels – both biofuels and fossil fuels The Sun’s energy is produced by through the process of nuclear fusion in its core Nuclear fusion involves the collision (and bonding) of hydrogen nuclei to form helium nuclei, releasing nuclear energy in the process Some forms of energy, however, do not come from the Sun These include: Geothermal – this comes from heat produced in the Earth’s core Nuclear – this comes from elements which make up a small proportion of the Earth’s crust Tidal – this comes (mainly) from the gravitational attraction of the moon © copyright Save My Exams CIE IGCSE Physics Resources Page 94 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7.4 EFFICIENCY Efficient & Inefficient Systems Whenever energy is transferred from one form to another, some of that energy is usually wasted and is transferred away from the system, usually in the form of heat or waves (light and sound) Whenever energy is transformed, some of the original energy usually ends up in an unwanted (wasted) form © copyright Save My Exams CIE IGCSE Physics Resources Page 95 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ An efficient system is one where most of the energy going into that system ends up in the form that is wanted Eg. An LED light bulb is efficient because most of the electrical energy (90%) ends up as light An inefficient system is one where most of the energy ends up in forms that weren’t wanted Eg. An old incandescent light bulb is inefficient because only a small amount of the electrical energy (5%) ends up as light Sankey diagrams comparing modern and old light bulbs © copyright Save My Exams CIE IGCSE Physics Resources Page 96 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Calculating Efficiency The efficiency of a system is the percentage of energy transferred from the original store that ends up in the intended form Efficiency can be calculated using the following equation: Efficiency can also be written in terms of power) the energy per second): © copyright Save My Exams CIE IGCSE Physics Resources Page 97 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7.5 WORK Work Done Energy is the capacity of something to do work Work is done whenever a force acts on an object that moves (or is moving) in the direction of the force The greater the force, the greater the work The larger the distance moved, the larger the work Work is done when a force is used to move an object a distance © copyright Save My Exams CIE IGCSE Physics Resources Page 98 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Whenever any work is done, energy gets transferred (mechanically) from one form to another The amount of energy transferred (in joules) is equal to the work done (also in joules) energy transferred (J) = work done (J) Usually, if a force acts in the direction that an object is moving then the object will gain energy If the force acts in the opposite direction to the movement then the object will lose energy © copyright Save My Exams CIE IGCSE Physics Resources Page 99 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Calculating Work Done The amount of work that is done if related to the size of the force and the distance moved by the object in the direction of the force: work done = force × distance moved W = F× d You can rearrange this equation with the help of the formula triangle: Use the formula triangle to help you rearrange the equation The units of work are joules (J) (the same as the units of energy), but can also be given as newton metres (Nm) © copyright Save My Exams CIE IGCSE Physics Resources Page 100 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ 1.7.6 POWER Power, Work Done & Time Taken Machines, such as car engines, transfer energy from one form to another every second The power of a machine is the rate at which the machine transfers energy The greater the rate at which energy is transferred, the greater the power Two identical cars accelerating to the same final speed will both gain the same amount of energy. But if one of them reaches that speed sooner, it will have a greater power Because work done is equal to energy transferred, the power is also equal to the rate of doing work © copyright Save My Exams CIE IGCSE Physics Resources Page 101 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics ⬇ Extended Only Calculating Power Power is the amount of energy transferred (or work done) every second. Power, work and time are related by the following equation: You can rearrange this equation with the help of the formula triangle: © copyright Save My Exams CIE IGCSE Physics Resources Page 102 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Physics Revision Notes savemyexams.co.uk YOUR NOTES 1. General Physics