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# P4 lesson part two

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### P4 lesson part two

1. 1. Explaining motion Route map Over the next 12 lessons you will study : Friday 21 October 2011 P4.1 Forces in all directions P4.2 How objects start to move P4.3 Friction P4.4 Reaction of surfaces End of module test P4.5 How fast P4.6 Modelling motion P4.7 Force, interaction and momentum P4.8 Change in momentum P4.9 Car safety P4.10 Laws of motion P4.11 Work and energy P4.12 Kinetic and gravitational potential energy
2. 2. P4.7 Force, interaction and momentum Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand what the term momentum means </li></ul><ul><li>Understand and know the link between change of momentum, force and time </li></ul>We will focus on. Friday 21 October 2011 First activity: Think of a bullet, is it the speed or mass of the bullet that makes it lethal. Think of a large HGV lorry, is it the speed or mass of the HGV lorry that makes it lethal ? Literacy: Momentum, force, time, change, mass, velocity, speeds, velocity, distance, metres, seconds, hours and kilograms. Numeracy: Momentum cab be calculate by multiply an object mass (Kg) by its velocity (ms -1 ). The momentum of an object depends on both its mass and velocity. This explain why you may die if hot by a slow moving bus an a fast moving bullet. PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers We will focus on review progress, acting on the outcomes.
3. 3. P4.7 Force interaction and momentum Extension questions: 1: What are the units of momentum ? 2: Work out the moment of a) a bullet travelling 500 ms -1 with a mass of 0.01 kg b) a tanker travelling at 0.01 ms -1 with a mass of 30,0000 kg c) a car travelling at 15 ms -1 with a mass of 1000 kg ? 3: A tennis ball hit a racket with a momentum of 10 kg m/s and returns over the net with the same speed has the tennis ball’s momentum changed ? 4: Explain using you knowledge of momentum why a wet leather football hurts much more when it hits you in the face ? Know this: a: Know what momentum is. b: Know that momentum links mass and velocity of a moving object. Friday 21 October 2011 Introduction: Momentum is the product of the mass and velocity of a moving object (momentum (kg m/s) = mass (kg) x Velocity (ms -1 ). Therefore momentum links the velocity and the mass of a moving object. Objects with high momentum impart lots of energy when they collide into us. Bullets kill you, not because of their mass which is usually around 5 to 10 g, but because of their very high velocities. A tanker can crush you to death even if it moves at very slow speeds of less than 0.01 ms -1 because it has a huge mass. Momentum also has a direction, so if it is moving in one direction, momentum is positive, if it moving in the opposite direction momentum is negative
4. 4. P4.7 Look at the photograph and information and answer all the questions: If an object is moving and has mass we can work out its momentum by multiplying its mass (kg) by its velocity ms -1 ) In urban areas, for example in cities, where people live, work and study road speed limits are reduced. This helps save lives because the momentum of a moving vehicle that may be involved in a crash is also reduced. Look at the diagram above left. Work out the momentum for the car travelling at 15 ms -1 with a mass of 1000 kg Explain why an accident involving a lorry is much more dangerous when compared to a similar accident involving a car ? Speed 10 ms -1 Mass 1,000 kg Momentum 10,000 kg m/s Speed 15 ms -1 Mass 1,000 kg Momentum .............. kg m/s Speed 10 ms -1 Mass 15,000 kg Momentum 150,000 kg m/s Speed 15 ms -1 Mass 15,000 kg Momentum ............... kg m/s 20mph 30mph Look at the diagram below left. Work out the momentum for the lorry travelling at 15 ms -1 with a mass of 15,000 kg Momentum of a car Momentum of a lorry 20mph 30mph
5. 5. Key concepts P4.7 Look at the photograph and information and answer all the questions: We all know that a ‘head on’ collision between two vehicles results in far more damage to both vehicles when compared to a crash when both vehicles are travelling in the same direction. Crashed involving large cars or lorries are even more dangerous because their huge mass gives them very high momentum. Using you knowledge of momentum explain why there is much greater damage when both are involved in a head on crash ? Speed 10 ms -1 Mass 15,000 kg Momentum 150,000 kg m/s Speed 30 ms -1 Mass 1,000 kg Momentum 30,000 kg m/s Speed 10 ms -1 Mass 15,000 kg Combined Momentum 150,000 – ( - 30,000) = 180,000 kg m/s Speed 30 ms -1 Mass 1,000 kg Momentum before collision Momentum during a collision Two cars travelling in the opposite direction crash. Car A is travelling at 30 m.p.h Car B is travelling at 40 m.p.h. Explain why this car is like a single car crashing into a brick wall at 70 m.p.h. If car C travelling at 12 m.p.h crashes into car D who is revising at 12 m.p.h. Would their be any damage to either car ?
6. 6. P4.7 Plenary Lesson summary: direction velocity zero postive Friday 21 October 2011 Momentum links velocity to an objects mass and helps us understand why two factors an objects speed and mass must be taken into account when assessing whether a collision with that moving object results in serious injury or eve death How Science Works: Research into what happens when a force is applied over a long period that leads to a change in an object’s momentum. Preparing for the next lesson: Momentum is measured in _______ and links the ______ of an object and its _________. An stationary object with a speed of 0 ms -1 has a momentum of ________. Momentum also has a negative and _________ value depending on its direction . Decide whether the following statements are true or false : False True 3: A bullet has a large momentum because of its high velocity ? False True 2: Large vehicles although travelling slowly have large momentums ? False True 1: Momentum can be calculated by adding an object’s mass and velocity ?
7. 7. P4.8 Change in momentum Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand the link between change of momentum, fore and time </li></ul><ul><li>Understand that momentum has a negative and positive value depending on the moving object’s direction </li></ul>We will focus on. Friday 21 October 2011 First activity: Using you understanding of momentum explain why more damage occurs when two vehicles travelling the opposite direction crash, when compared to two vehicles that are travelling in the same direction ? PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers Literacy: Momentum, force, time, change, mass, velocity, speeds, velocity, distance, metres, seconds, hours and kilograms. Numeracy: Momentum cab be calculate by multiply an object mass (kg) by its velocity (ms -1 ). The momentum of an object depends on both its mass and velocity. This explain why you may die if hot by a slow moving bus an a fast moving bullet. We will focus on trying out alternatives or new solutions and follow ideas through
8. 8. P4.8 Change in momentum Know this: a: Know the link between size of force, time that force acts on an object and the objects change in momentum. b: Know that the direction of momentum can affect the value of the change in momentum. Friday 21 October 2011 Introduction: If you push an object it will start to moving. Continue to push it and it will get faster and faster. By pushing this object you are changing the momentum of the object. The change in momentum depends on two things: 1: The size of the push force and 2: The time that this push force acts on the object Working out change in momentum: Change in momentum (kg m/s) = force (N) x time for which it acts (s) When two objects interact, the change in momentum of one is equal in size to the change of momentum of the other but in the opposite direction. Put simply: When two objects interact, the total change in momentum of the two objects is zero. This means that momentum before and after a collision is the same. We call this the conservation of momentum. Extension questions: 1: When a resultant force makes an object move, which two factors determine the change in momentum of the object ? 2: Which of the following will cause the large change in momentum on a 1kg ball a) 40N force acting for 2 seconds b) 30N force acting for 3 seconds ? 3: Which of the following will cause the smallest change in momentum on a 1 kg ball a) a 10N force acting for 10 seconds or b) a 9N forces acting for 12 seconds ?
9. 9. P4.8 a Look at the photograph and information and answer all the questions: In the diagram above left, If skater two only weighed 40 kg, work out his new speed if his total momentum was 240 kg ms -1 In the diagram below left, a man weighing 60 kg and a speed of 5 ms- 1 pushes a trolley with a mass of 15 kg. Work out the trolley's momentum (trolley travels same speed) 60 kg 4 ms -1 80 kg 3 ms -1 Conserving momentum 15 kg 5 ms -1 60 kg 5 ms -1 Understanding the conservation of momentum allows us to work out the speed of two moving objects after an interaction. Look at the two skaters opposite left. They push against one another. Skater one has a speed of 3 ms -1 and a mass of 80 kg. His momentum is therefore (80 x 3) 240 kg ms -1 . Skater two has the same momentum of 240 kg ms -1 . His mass is only 60 kg so his speed must be (240/60) 4 ms -1 . Key concepts
10. 10. P4.8 b Look at the photograph and information and answer all the questions: When two balls of equal mass collide as shown opposite left, momentum is not conserved. Explain why this is so in the real world ? Give two other examples similar to the example picture opposite left where two balls collide conserving momentum ? before collision after collision First ball momentum = mass x velocity First ball momentum = 0 (standing still) Second ball momentum = 0 (standing still) Second ball momentum = mass x velocity P = m x v P = m x v A collision between two balls of equal mass is a good example of an almost totally elastic collision. Due to the ball’s high rigidity; a totally elastic collision exists only in theory, occurring between bodies with mathematically infinite rigidity. In addition to momentum's being conserved when the two balls collide, the sum of kinetic energy before a collision must equal the sum of kinetic energy after: This is called the conservation of momentum Key concepts
11. 11. P4.8 Plenary Lesson summary: opposite objects change equal Friday 21 October 2011 In real life the momentum of a collision between two objects is never conserved, energy is lost because no object has infinite rigidity. This energy is lost in the from of heat (when material are squeezed) and sound (the noise of the collision) How Science Works: Research into how cars have been designed with safety feature that help us survive a collision. Also look at how the seat belt work if we do have a collision. Preparing for the next lesson: When there is an interaction between two ______, the ________ of momentum of one is _______ in size to the change of momentum of the other but in the _______ direction. Decide whether the following statements are true or false : False True 3: A bullet has a high momentum because it has a large mass ? False True 2: For the same object , its momentum increase as it velocity increases ? False True 1: Momentums depends on an object’s mass and velocity ?
12. 12. P4.9 Car safety Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand that cars have in built safety features </li></ul><ul><li>Understand how a seat belt spread the change of momentum during a collision, therefore reducing serious injury in humans </li></ul>We will focus on. Friday 21 October 2011 First activity: Prior to 1996, drivers and passengers in the front of a car were not obliged to wear seat belts. Following a change in the law, hospitals reported less fatalities due to car accidents. Was changing the law the right thing to do ? Literacy: Vehicles, collision, accident, safety, design, cars, passenger cage, roll bars, air bags, bumpers, crumple zones, brakes, anti-lock brakes . Numeracy: Over 3000 people a year are either serious injured or die as the result of collisions between cars, lorries and buses. Due to good safety feature less people die in 2010 when compare to 1990. PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers We will focus on supporting conclusions using reasoned arguments and evidence
13. 13. P4.9 Car safety Extension questions: 1: Explain why airs help reduce the force of impact between the driven and the steering wheel during a collision ? 2: Explain why a seat belt is made from a) wide webbing rather than narrow webbing and b) wide webbing that stretches rather than webbing that did not stretch ? 3: At the front and rear of cars are crumple zones. Explain how these zones help to reduce the impact force during a collision ? 4: Explain why its not speed that kill but the rate at which your speeds changes during a collision that kills ? Know this: a: Know that cars have safety features. b: Know how the seat belt works to save lives. Friday 21 October 2011 Introduction: Automobile safety is the driving within road speed limits, experience and car design. Car snow have role cages, impact crumple zones, seat belts, bumpers, air bags and soft material should you collide with part of the car. Car design started to change when SAAB first introduced a safety cage in 1948. Bumpers, crumple zones, seatbelts and finally air bags then followed. Software is now being developed to help cars and the driver avoid collision with other cars.
14. 14. P4.9 Look at the photograph and information and answer all the questions: How seat belts work Direction Seatbelt restraining The task of the seatbelt is to stop you with the car so that your stopping distance is probably 4 or 5 times greater than if you had no seatbelt. A crash which stops the car and driver must take away all its kinetic energy, and the work-energy principle then dictates that a longer stopping distance decreases the impact force. For the example imaging this car crash scenario: the stopping distance is one foot, the force on a 70 kg driver is about 2100 kg or 2.1 tons, and the deceleration is about 30 g's. A moderate amount of stretch in the seatbelts will reduce the average impact force. 0.0 s 0.2 s Look at the diagram opposite left. With out a seat belt it takes about 0.07 of a second for your forehead to hit the front dashboard of the car. With a stretchy seat belt this time is almost tripled to 0.2 seconds. By tripling the time what affect would this have of the force of impact between the driver’s forehead and the front dashboard ? Key concepts
15. 15. P4.9 Plenary Lesson summary: reduced save time windscreen Friday 21 October 2011 With all the additional safety feature, do we have less or more deaths due to road accidents. Well although it did first decrease the number of road deaths, it has now stayed the same. This is because when people feel safer or more protect because of seat belts air bags e.t.c they actual drive faster and take more risks How Science Works: Research into the forces that act on a cyclist when stationary, when accelerating and when moving at constant speed. Preparing for the next lesson: Seatbelt worn by passengers in the front ad back of a car helps _______ lives by increasing the ______ it takes a human to hit either the front dashboard, or __________ .By increasing the time the force of impact is greatly ___________. Decide whether the following statements are true or false : False True 3: Seat spread the change of the drivers moment over a longer time period ? False True 2: Wide stretchy seat belts work best at reduce the force of impact ? False True 1: Children do not have to wear seat belts under the age of 14 ?
16. 16. P4.10 Forces acting on a cyclist Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand about the laws of motion that apply to everyday moving objects </li></ul><ul><li>Understand that a resultant force is required to change an objects speed </li></ul><ul><li>Understand the forces acting on a cyclist </li></ul>We will focus on. Friday 21 October 2011 First activity: What forces are acting on a cyclist when they are going down a hill. Draw a simple diagram and show all the forces and the direction those forces ? Literacy: Motion, distance, time, forces, opposite, balanced, unbalanced, laws, resultant, air resistance, driving forces and counter forces Numeracy: An object at rest or travelling at a steady or constant speed has a pair of contact forces acting on it which are equal in size but opposite in direction. PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers We will focus on exploring issues, events or problems from different perspectives
17. 17. Extension questions: 1: List two examples where the resultant forces acting on an object is zero ? 2: List two examples where there is a resultant forces acting on an object ? 3: Explain how reducing air resistance between a cyclist and the atmosphere helps increase its speed ? 4: Explain why a cyclist’s speed will slow when the cyclist moves form a level surface to an incline ? Know this: a: Know the two laws of motion. b: Know the forces acting on a cyclist at the start, when accelerating and when moving at a constant speed. Friday 21 October 2011 Introduction: Thinking about a cyclist stetting off accelerating and hen reaching a constant speed helps us understand about the two laws of motion. Law one: If a resultant force acting on an object is zero then the momentum of the object does not change Law two: if there is a resultant force acting on an object, the momentum of the object will change. This can be calculating by using the following equation: Change in momentum = resultant force (N) x time for which it acts (s) P4.10 Forces acting on a cyclist
18. 18. P4.10 Look at the photograph and information and answer all the questions: At the start of the riders time trial, law two of motion applies where there is a resultant force acting on the cyclist, the momentum of the cyclist will change. During the race law two of motion applies where the resultant force acting on the cyclist and his bike is zero then the momentum of the object does not change For the bottom picture: Work out the following true or false: true false Gravity is pulling the bike down There is no friction The forces are unbalanced The forces are balanced The is no air resistance There is a pushing force Key concepts
19. 19. P4.10 Look at the photograph and information and answer all the questions: Look at the three diagrams opposite left. Explain how a cyclist can increase his maximum speed on level ground ? Explain how a rusty chain might reduce the top constant speed of a cyclist ? Driving force Counter force Setting off Going faster Constant speed Driving force Counter force Driving force Counter force When a cyclist being their ride, the counter force is small when compared to the driving forces. The end result of this is that the cyclists speed increases. As the cyclist goes faster, the air resistance force becomes larger, so the counterforce is large. Speed is still increasing but not as rapidly. Eventually a cyclist will reach a speed where the counter force and the driving force are equal but opposite and the cyclist continues to travel at a steady speed. 0mph 10mph 20mph Key concepts
20. 20. P4.10 Plenary Lesson summary: opposite forces equal internal Friday 21 October 2011 Most speed distance records for example the greatest distance travelled in one hour are done at altitude. This is because these are less air molecules. This reduce the air resistance between the bike and the air which can lead to an increase of speed or distance covered. How Science Works: Research into work, examples of useful work and how we calculate work done in joules. Preparing for the next lesson: During a constant steady speed, the resultant ________ acting on a cyclist are _______, but acting in opposite directions. In the __________ direction is push force of the leg muscles. In the opposite direction is the combination of _________ resistance, air resistance and friction between the road and wheels. Decide whether the following statements are true or false : False True 3: At 20 m.p.h 75% of the cyclist’s effort is used to overcome air resistance ? False True 2: Friction between he road and tyre acts to speed the cyclist up ? False True 1: When the cyclist is not moving the resultant forces acting are zero ?
21. 21. P4.11 Work and energy Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand how to calculate the work done by a force </li></ul><ul><li>Understand the link between work done on an object and the energy transferred </li></ul><ul><li>Understand the energy of moving objects linking velocity and mass of that object </li></ul>We will focus on. Friday 21 October 2011 First activity: Give five everyday examples (e.g. pushing a car along a roads) where work is done ? Literacy: Energy, mass, velocity, work done, forces, resultant, balanced, unbalanced, kinetic energy, joules and kilojoules. Numeracy: The energy of a moving object can be calculated by using the formula K.E = ½ mv 2 . this means that a car travelling 20 ms -1 with a mass of 1000 kg has a kinetic energy of ½ x 1000 x (20) 2 which is equal to 200,000 J or 200 kJ PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers We will focus on trying out alternatives or new solutions and follow ideas through
22. 22. P4.11 Work and energy Extension questions: 1: Work out the work done for the following scenarios a) pushing a car with a force of 1100N over a distance of 10 metres b) pushing a pram with a force of 80 N over a distance of 1000 m ? 2: In which of the following examples has most work be done a) pushing a trolley with a force of 75 N over a distance of 500 m or b) pushing a car with a force of 1100 N over a distance of 25 m ? 3: Work out the work done when a suitcase weighing 200 N is raised 2 metres about ground level and b) if he climbs the stairs weighting 600 N with the suitcase through a vertical distance of 3 m ? Know this: a: Know how to calculate work done by a force. b: Know that work done is measure in joules. Friday 21 October 2011 Introduction: Energy or a force is required to do work like lifting, pulling, pushing and stretching. In science, work is done if a force pushes, pulls, stretches or lifts an object with a mass. The amount of work done is always measured in joules: The amount of work done depends on the force exerted on an object and the total distance moved in the direct on the force. Work done is always measured in joules. Therefore the amount of work done is the force multiplied by the distance moved. Work done = force (N) x distance moved in the direction of the force (m) (units joules)
23. 23. P4.11 Look at the photograph and information and answer all the questions: Doing work always involves exerting a force in a particular direction for a certain distance in metres. Work done is always measured in joules. If you break down and have to push a car, the work done (flat road) is to over the internal resistance of the car. The greater the distance that you push the car, the more work is also done In the diagram above left, it shows that pushing a car 20 metres requires 16,000 joules of 16 kJ or energy. Work out how many joules of work would be used if you had to push the car over a) 50 metres b) 100 metres and c) one kilometre (1000 m) ? Look at the diagram below left. It shows a many pushing a supermarket trolley on a flat surface. When the man pushes the trolley what forces is he overcoming and b) work out the total work done when he pushes the trolley for 3 metres ? Push force 16 N 3 metres in distance 20 metres in distance Push force 800 N Pushing a trolley Pushing a car Work done = force x distance moved in direction of force = 800N x 20 m = 16,000 J or 16 kJ Work done = force x distance moved in direction of force = .......N x ...... m = ........... J or ...... kJ Key concepts
24. 24. P4.11 Plenary Lesson summary: joules newtons force metres Friday 21 October 2011 A small hatchback car can go about 15 kilometres using a single litre of fuel which costs about £1.10 at the petrol pumps. 10 men each applying a force of about 100N pushing the same car for over 3 hours would do the same amount of work. Remember also that the engine is only about 15% efficient, at transferring the chemical energy in petrol to work done by the car’s engine How Science Works: Research into kinetic and gravitational potential energy. Preparing for the next lesson: Work done measured in ________ can be worked out by multiplying the _____ measure in _________ by the _______ moved in the direction of the force measured in _______. Decide whether the following statements are true or false : False True 3: The units for work done joules or kilojoules ? False True 2: A lift loses gravitational potential energy as it ascends a skyscraper ? False True 1: Pushing a car or pram are both examples of work being done ?
25. 25. P4.12 Kinetic and gravitational potential energy Decide whether the following statements are true or false: <ul><li>Lesson objectives: </li></ul><ul><li>Understand that work done can change the kinetic energy of a moving object </li></ul><ul><li>Understand that work done can change the gravitational energy of a moving object </li></ul><ul><li>Understand how to sue energy ideas to picture the motion of objects </li></ul>Friday 21 October 2011 First activity: Work out the following using either K.E = ½ mv 2 or G.P.P = weight (N) x vertical height (m) Which has more kinetic energy a lorry with a mass of 10,000 kg travelling at 5ms -1 or a car with a mass of 1000 kg travelling at 15 ms -1 . People jump form the golden gate bridge to commit suicide. They fall 125 metres from bridge to sea. If a person had a weight of 750 N, Work out their G.P.E just before jumping ? PLTS Independent enquirers Creative thinkers Reflective learners Team workers Effective participators Self managers Literacy: Energy, kinetic energy, gravitational potential energy, work done, mass, velocity, work done, forces, resultant, balanced, unbalanced, joules and kilojoules. Numeracy: The gravitational potential energy of an object can be calculated by multiplying the weight (N) by the vertical height (m). This means that a person with a weight of 500N climbing vertically gains 500 joule of G.P.E every metre that they climb. We will focus on planning and carrying out research, appreciating the consequences of decisions
26. 26. P4.12 Extension questions: 1: If you jump form a wall, what happens to the gravitational potential energy as you fall ? 2: If you lift a 1000 kg weight 5 metres above the ground calculate its increase in GPE ? 3: Explain why a roller coaster on the surface of the moon would be less scary when compared to roller coasters here on Earth ? 4: A ball with a mass o 2k is on the 10 th floor of a skyscraper, 40 m above the ground,. Calculate its GPE and b) if it dropped calculate its final velocity using the equation K.E = ½ mV 2 ? Know this: a: Know how to calculate work done by a force. b: Know how to calculate kinetic energy of a moving object. c. Know how to calculate the GPE on an object. Friday 21 October 2011 Introduction: The kinetic or gravitational potential energy of an object is measured in joules. Kinetic energy of a moving object: KE = ½ mass x (velocity) 2 units kinetic energy (joules), mass (kg) velocity (ms -1 ) Gravitational potential energy GPE = weight x vertical height units GPE (joules), weight (N) height (m) Kinetic and gravitational potential energy
27. 27. P4.12 a Look at the photograph and information and answer all the questions: Understanding the kinetic energy of a car at different speeds, helps us understand why we have speed limits in towns and villages. If a child is hit at 20 mph (approx 10 ms -1 ) the child has a 80% chance of surviving. If the same car hits the same child at 40 mph (20 ms -1 ), the child has only a 20% chance of surviving. This is because we square the velocity to work out the energy of the car moving at a certain speed. A car travelling at 40 mph imparts 100 times the energy into a child’s body compared to a car travelling at 20 mph Look at the diagram of the kinetic energy of a moving car (above left) Work out the kinetic energy of a car with a mass of 900 kg and a velocity of 20 ms -1 ? Speed 10 ms -1 Mass 900 kg K.E 90,000 J or 90 kJ Speed 20 ms -1 Mass 900 kg K.E ............. J or ..... kJ Speed 1 ms -1 Mass 10,000 kg K.E 90,000 J or 90 kJ Speed 300 ms -1 Mass 0.01 kg K.E ............ J or ...... kJ Kinetic energy of the same object with different velocities Kinetic energy of objects with different masses Look at the diagram of the kinetic energy of a a lorry and a bullet (below left) Work out the kinetic energy of a bullet with a mass of 0.01 kg and a velocity of 300 ms -1 ? Key concepts
28. 28. P4.12 b Look at the photograph and information and answer all the questions: As a object gains vertical height, it increase its gravitational potential energy. When we are calculating the amount of work done in joules to lift a mass upwards against gravity, we must remember that it is the vertical height that we use in the calculation. The work done is transferred into gravitational potential energy, remember, when we move sides ways, no work is done because our bodies are not getting any higher Look at the diagram opposite left. Explain why the pulley on the left has zero GPE and b) work out the GPE for the right hand pulley ? Work out the GPE when a) a lift carrying 4 people over 50 m with a total weight of 15,000 N and b) a man (600 N) climbing the stairs ascending a vertical height of 25 m ? Work out the GPE of A man weighing 600 N walks up four flights of stairs. These stairs climb a total vertical distance of 20 metres ? Height 0 m Mass 1 kg GPE = height x weight Gravitational potential energy GPE = 0 x 10N = 0 J Height 10 m Weight 1 kg GPE = height x weight GPE = ... x .... = .....J Key concepts
29. 29. P4.12 c Look at the photograph and information and answer all the questions: Look at the diagram above left of the roller coaster and answer the following: a) At which point does the cart have maximum GPE and zero Kinetic energy b) At which point does the cart have zero kinetic energy and c) At which point does the cart have decreasing kinetic energy and increasing gravitational energy ? If you take a ride on any rollercoaster, at any theme park, designers exploit gravity and other forces to give you the ‘ride of your life.’ Gravity and the forces it exerts on your body will accelerate you from the start, giving you a sensation of falling. Rapid acceleration, twisting and turning gives you that sensation of a near vertical drop whilst still being safe. The force of gravity on a vertical drop rollercoaster pulls the mass of the car and you downwards, accelerating you at nearly 10 m/s 2 . Calculating the speed at C from B Loss of GPE = weight x vertical height = 120,000 N x 45m = 5,400,000 J K.E. = ½ mV 2 5,400,000 = ½ x 12,000 x V 2 V 2 = 5,400,000/6000 = 900 V = 30 ms -1 A B C D E Mass of cart = 12000 kg = 120,000 N: Vertical drop between B and C = 45 m: Value of ‘g’ on earth 10 Nkg -1 The roller coaster Key concepts
30. 30. P4.12 Plenary Lesson summary: potential force energy kinetic Friday 21 October 2011 Roller coasters are driven almost entirely by basic inertial, gravitational and centripetal forces, all manipulated in the service of a great ride. Amusement parks keep upping the ante, building faster and more complex roller coasters, but the fundamental principles at work­ remain the same. How Science Works: Revise for your end of module test. Preparing for the next lesson: Work connect __________ and energy. When you do work, you transfer ___________ to the object. This object with either speed up and increase its ________ energy or gain height therefore increasing its gravitational _______ energy. Decide whether the following statements are true or false : False True 3: When an object is falling it loses GPE and gains kinetic energy ? False True 2: Kinetic energy links the mass and velocity of an object ? False True 1: An object that is on the ground has zero GPE ?