GR 9 NS FORCES send.pdf

S Page 129 What is a force? Pushing + Pulling= twist  Effect of forces A force can cause an object to start moving. A force can cause a moving object to speed up, slow down or stop A force can cause an object to change its...

S Page 129 What is a force? Pushing + Pulling= twist  Effect of forces A force can cause an object to start moving. A force can cause a moving object to speed up, slow down or stop A force can cause an object to change its shape. A force can cause an object to rotate.  Describing forces Magnitude(size) and direction Force is measured in newton(N) named after Sir Isaac Newton (google him) 5 N acting downwards (northly) 16N acting to the right(westerly) 28 N south westerly force  Exercise 1 1.1 What is a forces? 1.2 List the effects of forces on any object 1.3 Give two everyday examples of the effects of forces 1.4 Describe the following forces in terms of direction and magnitude 10 N 17 N 80 N  A pair of Forces Forces always work in pairs When a force is applied to an object there is an equal resisting force acting in the opposite direction  Action and reaction pair of forces F₂ F F₂ The table pushes the ball The wall pushes you back If you push against wall The ball pushes the table F Contact forces Vs field forces Contact force Force exerted when two objects are in contact by touching each other. Field force(non-contact force ) Force exerted over a distance, objects without touching each other.  Types of contact forces Compression Squeezes object into a smaller space Friction-contact force that a surface exerts on an object. The frictional force always acts parallel to the surface. Always acts in the opposite direction to the movement of the object Tensional forces force in a rope or cable when a load is suspended or pulled  Gravitational force Force generated due to the object's mass acting on a gravitational field Gravitational force is a pulling force (attractive) that bodies exert on each The greater the mass the greater the gravitational force  In terms of gravitational force are you attracted to the person next to you? Each and every object with mass attract each other Newton's Law of Universal Gravitation. Sir Isaac Newton formulated a law that describes the gravitational force that two objects exert on each other. The gravitational force that two objects exert on each other become smaller as the distance between them increases  Exercise 2: identify the force Example : ) a soccer player running with soccer boots with studs underneath contact frictional 2.1 When a car breaks down and a cable is used to tow the car 2.2 If you pull an elastic band and it stretches 2.3 Rubbing two sticks together to start a fire 2.4 Squeezing a dish washing cloth 2.5 Jupiter pulling on its moons  Balanced and Unbalanced forces If more than one pair of forces act on an object Balanced When forces acting on an object are equal in size but opposite in direction with no visible effect on the object. Unbalanced forces unequal and in the opposite direction  Balanced forces The two forces acting on the books are the gravitational force on the books downwards and the force of the tabletop on the books upwards. These two forces acting on the box are balanced as they are equal in size and opposite in direction; they thus have no visible effect. No motion Balanced forces When a boy pushes against a wall and the wall does not move. This means that the forces acting on the wall are balanced. The two forces acting on the wall are friction and the applied force by the boy. The forces are equal in size and opposite in direction Unbalanced forces forces unequal More than one pair of forces can act on an object If more than one pair of forces act on an object will exclude the reaction force  Unbalanced forces If the force with which the boy pushes the box is greater than the force of friction, the box will begin to move as the forces acting on the box are now unbalanced. Pushing force one of the forces acting on the object is greater than the other and there will be a visible effect such as motion or change in shape.  Effect of gravitational force on objects Gravitational force on earth is so strong that you cannot float in the air But on the moon astronauts can jump very high and almost float over small distances.  Exercise 3 3.1 Redraw the diagrams but with labels to show the force exerted on the object A B Figure 2:planets Figure 1:books Figure 3:wall 3.2 What would happen in Figure 1 if the downwards gravitational force on the books is greater than the upwards force of the tabletop on the books  Exercise 4 A B 200 N PUSH 70Kg 50Kg Figure 3 150 N FRICTION Figure 2 4.1 Explain why does the tennis ball fall to the ground after the boy throws it up ? 4.2 Is the car in figure 1 moving or not moving explain your choice 4.3 Why is frictional force important when driving a car? 4.4 In figure 2,which rope experiences more tension and why? 4.6 Describe the usefulness or inconvenience of frictional force in everyday life Figure 1  Weight Vs Mass Mass is the amount of matter an object is made of. g /kg Weight is the product of mass and gravitational acceleration (newtons (N) Mass=5Okg Mass=5Okg Mass=5Okg Weight= 490.5 N Weight= 81 N Weight= 188.5 N Calculating weight Weight=mass X Gravitational acceleration = 5Okg X 9.81 = 490.5 N  Exercise 5 A B 5.1 Which of the surfaces above has more friction and why ? 5.2 Why does the ball on surface A slow down and stop. 5.3 Explain in terms of friction why does a man put a brick on the car trye  Exercise 6.1 6.1.1 Give differences between mass and weight. 6.1.2 Will a 50kg dumbell gravitate towards a 70kg human or will the 70kg human gravitate towards the 50kg dumbell? 6.1.3 Will a 5000g dumbell gravitate towards a 70kg human or will the 70kg human gravitate towards the 5000g dumbell? 6.1.4 Why do planets remain on orbit around the sun 6.1.5 If the gravitational force you exert on the earth is equal but opposite to the force the earth exert on you then why don’t the earth fall towards you? 6.5 Where will the gravitational pull be the least and why?  Exercise 6.2 6.2.1 Calculate the weight of following 6.2.1.1 A 80kg robot on Mars 6.2.1.2 A 80kg robot on earth 6.2.1.3 A 80kg robot on the moon 6.2.1.4 A 7005g robot on earth 6.2.1.5 A 1005g robot on Mars 6.2.2 An object has a mass of 25kg and a weight of 648.75 N in which planet is the object? 6.2.3 Looking the planets in our solar system establish a relationship between the mass of a planet and the gravitational force of a planet  Magnetic force Force that two magnetic materials exert on each other over a distance  What is a magnet? Material that attracts certain metals A magnetic field - is the area of magnetic force around a magnet material Earth has a magnetic field around it due to iron and Nikel core  Importance of earth’s magnetic field Protect us against harmful radiation Electronic communication Magnetic compasses Importance of earth’s magnetic field Bird seasonal migration Magnetic force can act THROUGH a non-magnetic substance Hand Wall Wood Paper Foil  Magnetic field Magnets always create a magnetic field Proving the existence of a magnetic field https://youtu.be/snNG481SYJw?si=gySi7qbtpk3rblX1 Magnet North pole and South pole  Attraction and repulsion Attraction unlike poles Repulsion like poles Magnetic field Attraction and repulsion fields s s s s  Exercise 7 7.1 Explain whether magnetism is a contact or non-contact force. 7.2 Differentiate repulsion from attraction forces 7.3 In which situation do magmatic bars repel each other 7.4 In which situation do magmatic bars attract each other 7.5 How do magnetic compasses guide us with directions 7.6 Give 4 Magnetic substances and 4 non-magnetic substances 7.7 Are gold and silver magnetic substances  Exercise 8 8.1 Draw a magnetic bar indicating the magnetic field. 8.3 Draw magnetic bars indicating the magnetic repulsion and attraction fields Electrostatic force  Electrostatic force A force that two electrically charged objects exert on each other over a distance Neural particles(atoms) +  Charged particles Negatively Charged Positively Charged + + Atoms gains electrons becomes electrically negative Atoms lose electrons becomes electrically positive A Electrostatic field exists around any charged object. How to charge particles https://youtu.be/owla5xPR268?si=AcfkOVF6eKYyrlKu https://youtu.be/vyp8YAyawmI?si=TkDK1OYa0U_zZyPw  Electrostatic force of repulsion Electrostatic force were particles push each other way due to like charges Electrostatic force of attraction Electrostatic force were particles pull to each other way due to unlike charges  Lightning electrostatic Positively charged top friction due to movement between water particles and air particles. Positively charged bottom Due to wind positively charged ground. Negative charges jump from clouds to the closest positive object on the ground with rapid expansion of air changing to heat and sound energy  Exercise 9 9.1 Define electrostatic force 9.2 How do you create an electrostatic field on a macro level? 9.3 How is an electrostatic field created on a micro level ? 9.4Why do you hear a crackling sound and see sparks when you take off your jersey? 9.5 How is lightning formed? 9.6 Give two safety precautions during lightning and thunderstorms.  Exercise 10 10.1 Draw a particle demonstrating a negatively charged electrostatic field 10.2 Draw a particle demonstrating a positively charged electrostatic field 10.3 Draw a diagram demonstrating of a positive electrostatic repulsion field 10.4 Draw a diagram demonstrating electrostatic attraction field 10.5 Draw a diagram demonstrating of a negative electrostatic repulsion field Electric circuits  Electric circuit …. a system that transfers electrical energy. Electrodes Solid material which an electric current enters or leaves a cell  Generation of electricity through electrodes Zinc plate and the copper Plate electrodes copper sulphate solution zinc sulphate solution ions (charged atoms) within a solution Electrolytes - a solution that provides a medium for ions to move and produce electricity. The chemical reaction makes electrons move from the zinc plate, through the conducting wire, to the copper plate. Generation of electricity through electrodes Nacl(aq) The purpose of the salt bridge is to keep the solutions electrically neutral and allow the free flow of ions from one cell to another. Zinc-Copper Galvanic Cell https://youtu.be/hd4hwkNH5YU?si=OG22p8jz2_IHjp5W Electrical Cell =unit of electrodes immersed in electrolytes to produce electricity Wet cells or Dry cells Liquid electrolytes Paste electrolytes EASY to recharge Difficult recharged Acidic cell Alkaline cell  Pair of electrodes Combination of cells Cell Vs battery Long line-positive terminal Short line-negative terminal. Combination of cells Battery  Electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space Light energy Heat energy Sound energy Electrical energy + Chemical reaction Chemical energy Input: - Electron flow Output Measuring electrical current(I) The strength of the current in an electric circuit is measured in amperes Measuring electrical current(I) Video https://youtu.be/yImSiaYGtwQ?si=jVtXbz-hVTrN9vJr Everyday cells and circuits Car batteries Cell phones Remote control devices Torches  Voltage (V) Potential difference across the terminals of the cell Measure of the amount of potential energy stored in a cell. The pressure from an electrical circuit TO pushes charged electrons through the conducting wire Increase in voltage The higher the voltage of a cell, the more energy each electron has available to moves through the circuit. This means that the more cells you connect, the higher the voltage of the battery  Measuring voltage We measure the voltage of a cell by connecting a voltmeter across its terminals. Video https://youtu.be/w82aSjLuD_8?si=1U-FMPMGyHv9YOx9 https://youtu.be/Hn2iIdZtY8A?si=BegAQWf9JNBrO5Dp  Exercise 11 11.1 Explain what happens in a Zinc copper plate electrode galvanic Cell 11.2 Explain the difference between a cell and a battery. 11.3 When a cell is connected to a circuit, chemical energy is connected to what type of energy? 11.4 What instrument is used to test chemical potential energy of a cell? 11.5 What instrument is used to test electrical current of a cell? 11.6 What does the brightness of the bulbs tell you about the voltage of the circuit? Symbols of a circuit Diagram representation of a circuit Open Vs Closed circuit Open Closed  Parallel and series When the circuit component are arranged in a single path. When the circuit component are arranged in more than one path. Diagram representation Parallel and Series series Parallel  Advantages Vs disadvantages Series connection -Series circuits are easier to connect and require less wiring. -Because of less wiring and switches series systems are cheap Parallel connection - Parallel circuits have a low total resistance, which increases the current and the power output of the circuit. - Component are independent of each other, if one component fails or is disconnected, the rest of the circuit still works. Protect appliances against high voltage electric surge such as lighting -Makes power source last longer  Exercise 12 12.1 Draw a circuit diagram that contains a cell and a bulb. 12.2 Draw a labelled circuit diagram of a cell and two bulbs in series with an ammeter connected in series with a closed switch 12.3 Draw a labelled circuit diagram of a cell and two bulbs in parallel with an ammeter connected in series with a closed switch 12.4 Draw a labelled circuit diagram of a battery with two cells and an ammeter connected in series along with a resistor and the voltmeter must reading the potential different across the resistor 12.5 Give advantages of connecting components in parallel 12.6 Give advantages of connecting components in series  Resistance (ohm (Ω)) Resistors are component of the circuits that control the flow of current in electrical circuits Current experiences resistance when the charged particles collide with the atoms of the of component through which they are moving.  Resistors Resistors convert electrical energy into heat, light and sound energy  Variable resistors Some resistors do not apply fixed resistance They have a mechanism that allows them to change their resistance.  Variable resistors Radio volume control knobs rheostats Diodes -are special electric components that control the flow of electric current A convert's electrical energy to light energy light-emitting diode (LED) A light-dependent resistor (LDR) Dimmer light switches  Factors affecting resistance The conducting wires in a circuit offer some resistance to the current flow in the circuit. Type of material of the resistors and conducting wire Length conducting wire The longer the conducting wire the higher the resistance Thickness of the conducting wire The thicker the conductor the lower its resistance. Temperature of the conducting wire The higher the temperature the more the resistance  Conductors and insulators Good electrical conductors offer low resistance to current flow ▪ Silver ▪ copper ▪ gold ▪ copper High electrical resistance(insulators) difficult for current to flow Wood rubber  Exercise 13 13.1List at least three electrical household appliances that uses resistor 13.2 Explain why conducting wires in a circuit also considered a resistors 13.3List and explain the factors that affect the resistance of the conducting wire in a circuit 13.4 What would happen to the resistance of the conducting wire if you increase the length of the conducting wire 13.5 What would happen to the resistance of the conducting wire if you increase the temperature of the conducting wire 13.6 What would happen to the resistance of the conducting wire if you increase the width of the conducting wire 13.7What would happen to the resistance of the conducting wire if you changed the material of the conducting wire from copper to wood ? Measuring resistance The unit of electrical resistance is the ohm (symbol: Ω) ohmmeter  Ohm's law Relationship resistance, current and voltage R = V/I Resistors with high resistance have lower current flow Resistors with low resistance have high current flow If voltage increases resistance also increases If voltage decreases resistance also decreases The higher the voltage the higher the current flow The lower the voltage the lower the current flow  Calculating Example 1 resistance, current and voltage A circuit has a current of 20 Amp flowing through it and the battery offers 15 volts potential difference across the circuit. Calculate the resistant of the only bulb in the circuit. R = V/I R = 15÷20=0.75 ohm  Calculating Example 2 resistance, current and voltage A circuit has potential difference 35 volts across the circuit with a resistant of 20 Ω across the only bulb in the circuit. Calculate the current flowing through the circuit R = V/I I = V/R I =35÷20=1.75 A  Exercise 14 14.1 Predict what would happen to the brightness of the bulbs if you connected a more cells in series. 14.2 Give a conclusion about the effect of the number of cells have on the current flow of a circuit 14.3 Give a conclusion about the effect of component resistance on the current flow of a circuit 14.4 Give a conclusion about the effect of voltage on the resistors of a circuit 14.5 Why is it best to always connect an ammeter in series? Exercise 15 Resistance (ohm) Current strength (A) 100 230 150 120 200 80 250 60 350 50 Diagram 1 Diagram 2 15.1 Looking at diagram 2 does the current flow start flowing upward or downward give a reason for your answer 15.2 Where will current flow the most between R2 and R1 give a reason for your answer ? 15.3 If you placed an ammeter over R3 what would it read 15.4 What is the total resistance of the circuit 15.5 Which one is the independent variable in diagram 1 and explain your answer 15.6 Which one is the dependent variable in diagram 1 and explain your answer 15.7 Use diagram 1 to draw a labelled line graph. LEMON https://youtu.be/AWEdpTOtL6M?si=q-zWo_2o1ZoPf1fZ https://youtu.be/WNx-bwlTATI?si=3Tatr6dcoWRyeqZi TIP FOR THE TEST Study all the exercises Class tests-Choose 4 Class test 1 Class test 8 Class test 2 Class test 9 Class test 3 Class test 10 Class test 4 Class test 11 Class test 5 Class test 12 Class test 6.1 Class test 13 Class test 6.2 Class test 14 Class test 7 Class test 15 Short circuit When electrical current takes an unintended NEW path (shortcut) causing an overflow of electricity current  Causes Short circuits Damaged wires Wrong resistors(to much or to little resistance) Appliance overload Wrong wire connections short circuits Prevent Short Circuits: Fix Faulty Appliance and wiring Do an Occasional Electrical Inspection Fix Wire Insulation Fix Loose Wire Connection Exercise 16 16.1 Describe the above observation in one word ? 16.2 What causes it how can it be prevented ? Electricity Safety mechanisms Earth leakage system Fuses Circuit breaks THREE- PIN PLUG (brown or red) RED/BROWN- live wire is the current supply BLUE- neutral wire is the return path during normal operation completing the circuit YELLOW/GREEN -earth leakage wire carries no current during normal operation but feeds current into the ground during faulty operations  Circuit breaker electromagnetic technology that break current flow “Main switch” If the amount of current becomes too large, contacts (Main switch) are broken and the current stops flowing. Circuit board will trip, and the switch will turn off. Someone must reset the circuit breaker before current can flow again. Different Circuit breakers Circuit breaker symbol  Earth leakage system When electric current unintentionally flows to the ground instead of completing the circuit path due to damaged insulation or other electrical issues. Neutral wire Earth wire Live wire  Fuse a safety device consisting of a thin strip of metal that melts and breaks if the current overload/exceeds the safe level circuit symbol  Exercise 17 17.1 Define overload in electricity 17.2 Why are there different current values written on different circuit breaker? 17.3 A 20 mA is written on an earth leakage connection what does the value mean ? 17.4 What is the function of a circuit breaker? 17.5What is the function of a fuse 17.6 What the difference and similarities between earth and neutral wires 17.7 What are Earth leakage systems 17.8 What happens if there is difference in current flow between the live wire and the natural wire? 17.9 Even though it is wise for electrical circuits in houses to be always connected in parallel to ensure that lights and plugs can be operated independently but what could be wrong if you overload the system ? 17.10 Discuss how earth leakage system protect people from being electrocuted by electric devices.