Lower Secondary Science - Transportation Science - Forces PDF

Lower Secondary Science - Transportation Science - Forces MODULE 2: Transportation Science SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces DISCIPLINE TRANSPORTATION SCIENCE...

Lower Secondary Science - Transportation Science - Forces MODULE 2: Transportation Science SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces DISCIPLINE TRANSPORTATION SCIENCE SCIENCE DEPARTMENT TOPIC DIVERSITY / INTERACTIONS / MODELS / SYSTEMS THEME Motion Science of Modes of EU/EQ Describing Causes of Energy Transport Transport Motion Motion Transfers Describing Land UNIT MODELS Sources of Motion Air Forces Energy Causes of Motion Sea Transfer of Moments Energy Space Speed Energy Density & DIVERSITY SYSTEMS Transfers Pressure Talks / INTERACTIONS Performance Learning LESSON Classroom lessons employing Tasks Journeys Applied Learning and Technologies SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces UNIT 2: Forces (The cause of motion) SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Knowledge Types of forces Friction Mass and weight Effects of forces Free-body diagrams Newton’s laws SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Cognitive Skills (a) Use the Newton as the SI unit of a force. (b) Show an understanding that a force can be a contact or non-contact force. e.g., contact force (friction, tension); non-contact force (magnetic force, gravitational force) (c) State that mass is a measure of amount of matter or substance in a body. (d) Define weight as the amount of gravitational force acting on a body. (e) Compare weight and mass. (f) Predict effects of forces on an object (e.g. how tides are caused by gravitational interaction between the oceans and the moon) (g) Show curiosity about the destructive power of forces in nature (e.g., earthquakes, tsunamis, volcanic eruptions, tropical cyclones) SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Cognitive Skills (h) Recognise that the interactions between two or more objects, result in a transfer of energy which can/may cause changes (by application of force) to the: state of rest or motion of an object; size and/or shape of an object; turning effects in objects (e.g., spanners, levers to open tins); pressure on objects (i) Draw Free Body Diagrams. (j) Demonstrate understanding that when forces are balanced, a stationary object remains stationary and a moving object continues moving at the same speed in a straight line [Newton’s 1st Law]. (k) Demonstrate understanding that when forces are unbalanced, an object changes its state of rest or constant motion changes its size or shape changes its direction [Newton’s 2nd Law]. (l) Demonstrate understanding that a force is a type of interaction between two objects [Newton’s 3rd Law]. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Practical Skills Practical Skills (a) Measure accurately force, mass and weight of matter using appropriate instruments (Newton-meter, electronic balance) and methods. (b) Demonstrate precision and accuracy in making measurements (taking into consideration random and systematic errors such as parallax and errors). SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 3. Forces SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.1 What is a force? A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.1 What is a force? The interaction causes a transfer of energy, which can – change the state of rest or motion of a body – change the size and/or shape of a body – bring about turning effects in objects (e.g. levers) – exert pressure on objects The S.I. unit of forces is the newton ( N ) and a Newton-meter / Spring Balance is used to measure a force. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.2 Types of forces There are many types of forces. Forces can be contact or non-contact (action-at-a-distance). Tick the correct ones. You may check the internet for answers. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.2 Types of forces Non-co Name of Non-co Name of force Contact Contact ntact force ntact Air resistance / Normal Drag force force Buoyant Friction force / Up-thrust Weight Thrust SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.2 Types of forces Non-co Name of Non-co Name of force Contact Contact ntact force ntact Air resistance / Normal YES YES Drag force force Buoyant Friction YES force YES / Up-thrust Weight YES Thrust YES SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.3 Friction and its effects Friction is a force that opposes motion between 2 surfaces in contact – depends on the materials in contact. – depends on the nature of surfaces in contact. – is proportional to the force pressing the surfaces together. – does not depend on the area of contact. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Negative Effects of Friction Reduces efficiency of cars by up to 20% Causes wear and tear of moving parts in engines, motors and machines SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Positive Effects of Friction Needed for walking or holding a pair of chopsticks Used in braking pads to slow down cars SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Importance of friction in walking When the leg pushes backwards, The ground exerts a friction force forwards (friction). Allowing the person to walk. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Application of friction to Mousetrap car The mousetrap car project is an awesome way for young students to learn how to tweak different variables in order to enhance the performance of a vehicle design. In mousetrap car, friction is needed at some places and friction is not needed at some places. What areas are they? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces We need to reduce friction between SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Ways to Reduce Friction Rolling action – Wheels – Ball bearings Smoothens surfaces – Lubricants – Polishing surfaces SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces We need to increase friction between SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Ways to increase Friction Grip the roads better – Wider wheels – Rough wheels – Materials used SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.4 What is Mass? Mass is a measure of the amount of matter or substance in a body. The unit of the mass is the kilogram. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Fun fact: Are you aware that there are changes to the definition of the kilogram? The official object that defined the mass of a kilogram is a tiny, 139-year-old cylinder of platinum and iridium that resides in a triple-locked vault near Paris. (a) What is the problem with this method of defining mass? ……..……..……..……..……..……………………… ….…..……..…….. (b) What is a better way to define the kilogram? ……..……..……..……..……..……………………… …...……..……..… SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Fun fact: Are you aware that there are changes to the definition of the kilogram? The official object that defines the mass of a kilogram is a tiny, 139-year-old cylinder of platinum and iridium that resides in a triple-locked vault near Paris. (a) What is the problem with this method of defining mass? The mass will get lesser each time it is taken out for measurement. (b) What is a better way to define the kilogram? Use a standard that is based on a constant that is unchanging. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.5 What is weight? Weight is the gravitational force acting on a body. How are mass and weight related? Weight = mass x gravitational field strength W=mg SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.6 What is gravitational field strength? Gravitational field is a region surrounding the object in which the gravitational force is experienced. As shown on the diagram on the right, a gravitational field surrounds Earth. Field lines are drawn to represent the gravitational field. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.6 What is gravitational field strength? Gravitational field strength, g, is defined as the gravitational force acting per unit mass on an object. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.6 What is gravitational field strength? The value of the gravitational field strength of an object depends on the object’s mass. The table below summarizes the gravitational field strength of several major bodies in our solar system. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces What can you conclude from the above trend relating to mass and gravitational field strength? ………………………………….…………… ……………………. ………………………………….…………… ……………………. ………………………………….…………… ……………………. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces What can you conclude from the above trend relating to mass and gravitational field strength? The greater the mass of planets, the greater the gravitational field strength. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 1 Jeremy measured his mass with an electronic balance on Earth and gets a reading of 60 kg. (a) What is his weight on Earth if the gravitational field strength of Earth is 10 N/kg? (b) What is his mass and weight on Moon if the gravitational field strength of Moon is one sixth that of Earth’s? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 1 Jeremy measured his mass with an electronic balance on Earth and gets a reading of 60 kg. (a) What is his weight on Earth if the gravitational field strength of Earth is 10 N/kg? Weight = 60 x 10 = 600 N (b) What is his mass and weight on Moon if gravity of Moon is one sixth that of Earth’s? Mass = 60 kg (no change on different planets) Weight = 60 x 10/6 = 100 N SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 2 A box weighs 500 N on Earth. It is loaded onto a space shuttle and dropped on the surface of planet Mars. The box weighs 185 N on Mars. (a) What is the mass of the box on Earth if the gravitational field strength of Earth is 10 N/kg? (b) What is the mass of the box on Mars? (c) What is the gravitational field strength of Mars? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 2 (a) What is the mass of the box on Earth if the gravitational field strength of Earth is 10 N/kg? Mass of box = weight / g = 500/10 = 50.0 kg (b) What is the mass of the box on Mars? Mass of box on Mars = 50.0 kg (no change) (c) What is the gravitational field strength of Mars? On Mars, g = W/m = 185/50 = 3.7 N/kg SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces 2.7 Distinguish between mass & weight Mass Weight Symbol m W Definition Measure of the amount of Gravitational force acting on a matter or substance in a body mass W = mg SI unit kilogram (kg) newtons (N) Changes with not affected by gravitational field affected by gravitational field location strength of the location strength of the location Measuring Calibrated electronic balances Electronic balance instrument Beam balances Spring balance SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces How are mass and weight measured? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces How are mass and weight measured? Beam Balance Electronic mass balance SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces How are mass and weight measured? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces How are mass and weight measured? Newton-meter Spring Balance SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Both instruments usually have mass and weight labels on it. Are there conditions to its use? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Both instruments usually have mass and weight labels on it. Are there conditions to its use? The instruments must be stationary when you are using it. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Are you able to use these devices above when you are in outer space? Explain your answer. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Are you able to use these devices above when you are in outer space? Explain your answer. No. The equipment require forces to be pulling on it to work properly. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.8 Gravitational Attraction Gravitational Attraction is a force that attracts objects towards each other. Any object with mass exerts a force of gravity with another body. The force of attraction between 2 bodies depends on the masses of the 2 bodies and the distances apart. o The greater the masses, the greater is the attractive force. o The further apart an object is to another, the weaker is the attractive force. The force of gravity is not very noticeable unless one of the objects – such as the Earth or the Sun – has a huge mass. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.8 Gravitational Attraction Gravity attracts objects towards the centre of the Earth SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.8 Gravitational Attraction Effects of Gravitational Attraction of the earth – pulls objects on Earth towards the centre of the planet – holds the Earth's atmosphere in place – holds all the components of the solar system in orbit around the Sun – holds all the components of the galaxy together SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.8 Gravitational Attraction Effects of Gravitational Attraction of the moon – Tides SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.8 Gravitational Attraction Effects of Gravitational Attraction of the moon – Tides You may read up on Tides on this Youtube video link: https://goo.gl/hWynPo SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.9 Effects of forces Earthquakes Tsunamis Volcanoes Cyclones, Typhoons, Hurricanes SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Explain the causes of earthquakes Movement of tectonic plates Edges of plates will rub against each other The friction between the plates will cause vibrations SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Earthquake Maps SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Explain the causes of Tsunamis When earthquakes happen near the seas Vibration of the soil/crust will cause vibrations in the seas Generating huge waves called Tsunamis SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Tsunamis Map SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Explain the causes of Volcanic eruptions Due to tectonic plate movements, magma flows through the cracks If there is a blockage, pressure will build up If the pressure is too strong, it will erupt as lava SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Volcanoes Map SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Explain the causes of tropical cyclones When there are 2 different regions with different temperatures, Air will flow between the regions. It will create strong winds and rainfalls. More answers can be found if you carry out research. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Cyclones / Typhoons / Hurricane Map SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.10 Free-body diagrams A free-body diagram is a pictorial representation that shows the relative magnitude and direction of forces acting on an object in a situation. Drawing a free-body diagram is typically the first step in analyzing and solving problems that involved forces. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Things to take note when drawing free-body diagram: Use a box to represent the object of interest Use arrows to represent the force on the object Label the arrows with the appropriate types of forces The arrows must show the relative magnitude and direction of forces (i.e. a 5.0 N force must be drawn longer than a 2.0 N force). When drawing the force arrow, the arrow must be in contact with the object. When drawing the weight arrow, the arrow must start from the centre of the object. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 3 Draw the free-body diagram of the vertical forces acting on the laptop when it is placed on a table. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 3 Draw the free-body diagram of the vertical forces acting on the laptop when it is placed on a table. normal contact force weight Note: The force that the laptop acts on the table is NOT included. SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces Normal 1 2 3 Object falling 4 through air SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces 5 6 Box being pushed 7 8 SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces 1 Normal Contact Force Driving force F 2 Weight Normal Contact Force Driving force F 3 Friction, f Weight Object falling Air Resistance 4 through air Weight SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces 5 Air Resistance weight 6 Box being pushed Air Resistance Driving friction force F 7 lift Thrust drag weight 8 tension weight SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2.11 Balanced and Unbalanced Forces SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces st Balanced Forces: Newton’s 1 Law Newton’s 1st Law states that an object will remain at rest or move with constant speed in the same direction, unless it is acted upon by a net or resultant force. In other words, if no net or resultant force acts on the object, it will – not move if it is initially at rest or – continue to move with its initial speed in the same direction SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Balanced Forces No net or resultant force on an object does not mean no force is acting on the object. It’s simply means that all the forces acting on the body are balanced. An object at rest or at constant motion has zero rate of change of velocity (speed). SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Balanced forces Velocity is speed with direction SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 4 Draw in the forces acting on the following objects. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 4 Normal normal Tension Friction weight weight SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 5 A box is moving at a constant speed. It is pulled with a force of 20 N towards the right. If the frictional force acting on the box is 20 N, what is the resultant force acting on the box? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 5 A box is moving at a constant speed. It is pulled with a force of 20 N towards the right. If the frictional force acting on the box is 20 N, what is the resultant force acting on the box? normal 0N Pull 20 N Friction 20 N weight SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces nd Unbalanced forces: Newton’s 2 Law Effects of Forces on Motion When the forces acting on a body is unbalanced , the net force may – Cause a stationary body to move – Cause a moving body to stop – Change the speed of a moving body – Change the direction of a moving body SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Unbalanced forces Velocity is speed with direction SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 6 A box is pulled with a force of 30 N to the right. If the frictional force acting on the box is 20 N, what is the resultant force acting on the box? Describe the motion of the box if (a) the box is initially at rest; (b) the box is already moving to the right. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 6 A box is pulled with a force of 30 N to the right. If the frictional force acting on the box is 20 N, what is the resultant force acting on the box? Describe the motion of the box if (a) the box is initially at rest; (b) the box is already moving to the right. (a) Net force = 30 – 20 = 10 N to the right. The speed of the box will increase from 0 m/s. The box moves to the right. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 6 A box is pulled with a force of 30 N to the right. If the frictional force acting on the box is 20 N, what is the resultant force acting on the box? Describe the motion of the box if (a) the box is initially at rest; (b) the box is already moving to the right. (b) Net force = 30 – 20 = 10 N to the right. The speed of the box will increase to the right. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 7 The diagram shows a solid object on a flat surface, with two forces acting on the object. What is the resultant force on the object? A 1 N to the left B 1 N to the right C 7 N to the left D 7 N to the right SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 7 The diagram shows a solid object on a flat surface, with two forces acting on the object. What is the resultant force on the object? A 1 N to the left B 1 N to the right C 7 N to the left D 7 N to the right SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Action-Reaction Forces: rd Newton’s 3 Law Newton’s first two laws of motion explain how the motion of a single object changes. If the forces acting on the object are balanced, the object will remain at rest or stay in motion with constant velocity. This is Newton’s 1st law. If the forces are unbalanced, the object will accelerate in the direction of the net force. Newton’s 2nd law tells the change in velocity, of an object if the net force acting on it is known. Newton’s 3rd law describes something else that happens when one object exerts a force on another object. Suppose you push on a wall, it may surprise you to learn that if you push on a wall, the wall also pushes on you. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Action-Reaction Forces: rd Newton’s 3 Law According to Newton, if a body A exerts a force on a body B, then body B will exert an equal and opposite force on body A [Newton’s 3rd Law]. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Action-Reaction Forces: rd Newton’s 3 Law Note that: (a)The forces must act on 2 different bodies (b)The forces must be of the same type (e.g. Weight & Normal force are not a pair) (c) The forces must come in a pair (d)The magnitude (size) must be equal (same number of Newtons) (e)The directions must be opposite SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Action-Reaction Forces: rd Newton’s 3 Law Identify the action-reaction pairs of forces in the following cases, applying the concepts that have just been highlighted about action-reaction pair of forces above: SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 8(a): Draw the forces of interaction between the two boys. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 8(a): Draw the forces of interaction between the two boys. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 8(a): Who exerts a greater force? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces In an unfair tug-of-war, who exerts a greater force? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces In an unfair tug-of-war, who exerts a greater force? SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Hence, … Who exerts a greater force? Neither! The forces have the same magnitude. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 8(b): Draw the forces of interaction between the swimmer and the wall. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces 2 objects are to be drawn: Swimmer AND the wall. Normal contact force by the swimmer on the wall Normal contact force of the wall on the swimmer SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Example 8(c): Draw the forces of interaction between the box and the table. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Normal contact Force by table on the box Normal contact by the box on the table SCIENCE DEPARTMENT  Lower Secondary Science - Transportation Science - Forces rd Other examples of the Newton’s 3 Law: Walking: you push down and back Stubbing your toe: when you kit on the ground and it pushes back your foot on a rock it hits you with on you propelling you forward. an equal and opposite force. Riding a skateboard: you push Rowing a boat: you use the oars to backwards on the ground and it push the water backwards and it pushes you forward. pushes back on the oars in the Rockets: fuel is combusted and other direction. exhaust gasses are pushed out in Swimming: pushing off the wall the opposite direction of intended propels you forward because the motion. The gasses push back. wall pushes back on you. Releasing a balloon: the stretched Propeller of helicopter: pushes air rubber pushes on the air forcing it down and the air pushes back on it. out and the air pushes back on it. SCIENCE DEPARTMENT Lower Secondary Science - Transportation Science - Forces Thanks THE END SCIENCE DEPARTMENT