Subject: Triple Physics Unit title: P4.5 Forces (Paper 2) Strand Content Checklist (L) R A G Forces and their interactions

Transcription

1 4.5.3 Forces and elasticity Work done and energy transfer Forces and their interactions Subject: Triple Physics Unit title: P4.5 Forces (Paper 2) Strand Content Checklist (L) R A G 1. Identify and describe scalar quantities and vector quantities 2. Identify and give examples of forces as contact or noncontact forces 3. Describe the interaction between two objects and the force produced on each as a vector 4. Describe weight and explain that its magnitude at a point depends on the gravitational field strength 5. Calculate weight by recalling and using the equation: [ W = mg ] 6. Represent the weight of an object as acting at a single point which is referred to as the object's centre of mass 7. Calculate the resultant of two forces that act in a straight line 8. HT ONLY: describe examples of the forces acting on an isolated object or system 9. HT ONLY: Use free body diagrams to qualitatively describe examples where several forces act on an object and explain how that leads to a single resultant force or no force 10. HT ONLY: Use free body diagrams and accurate vector diagrams to scale, to resolve multiple forces and show magnitude and direction of the resultant 11. HT ONLY: Use vector diagrams to illustrate resolution of forces, equilibrium situations and determine the resultant of two forces, to include both magnitude and direction 12. Describe energy transfers involved when work is done and calculate the work done by recalling and using the equation: [ W = Fs ] 13. Describe what a joule is and state what the joule is derived from 14. Convert between newton-metres and joules. 15. Explain why work done against the frictional forces acting on an object causes a rise in the temperature of the object 16. Describe examples of the forces involved in stretching, bending or compressing an object 17. Explain why, to change the shape of an object (by stretching, bending or compressing), more than one force has to be applied this is limited to stationary objects only 18. Describe the difference between elastic deformation and inelastic deformation caused by stretching forces 19. Describe the extension of an elastic object below the limit of proportionality and calculate it by recalling and applying the equation: [ F = ke ] 20. Explain why a change in the shape of an object only happens when more than one force is applied Key Words (L) Newton: unit of force Scalar: magnitude(size) only Vector: magnitude and direction Speed: how fast something is moving gradient: the slope of the graph; change in the y-axis divided by the change in the x- axis Distance-time graph: graph with distance on the y-axis and time on the x-axis; the gradient is equal to the speed accelerating: rate at which an object speeds up, calculated from velocity divided by time decelerating: negative acceleration, when an object is slows down Velocity-time graph: graph with velocity on the y-axis and time on the x-axis; the gradient is equal to the acceleration; the area under the graph is equal to the displacement Resultant force: the single force that would have same effect on an object as the forces that are acting on the object Newton s 1 st Law: if the resultant force acting is zero, a stationary object will remain stationary ad a moving object will keep moving at a steady speed in a straight line Free-body diagram: drawing of an object showing precisely the magnitude and direction of the forces acting on that object Newton s 2nd Law: a resultant force on an object produces an acceleration in the same direction as the force that is proportional to the magnitude of the force and inversely proportional to the mass of the object; F=m*a inertia: natural tendency of objects to resist changes in their velocity

2 4.5.6 Forces and motion Pressure and pressure differences in fluid Moments, levers and gears 21. Describe and interpret data from an investigation to explain possible causes of a linear and non-linear relationship between force and extension 22. Calculate work done in stretching (or compressing) a spring (up to the limit of proportionality) by applying, but not recalling, the equation: [ E e = ½ke 2 ] 23. Required practical 6: investigate the relationship between force and extension for a spring. 24. State that a body in equilibrium must experience equal sums of clockwise and anticlockwise moments, recall and apply the equation: [ M = Fd ] 25. Apply the idea that a body in equilibrium experiences an equal total of clockwise and anti-clockwise moments about any pivot 26. Explain why the distance, d, must be taken as the perpendicular distance from the line of action of the force to the pivot 27. Explain how levers and gears transmit the rotational effects of forces 28. Describe a fluid as either a liquid or a gas and explain that the pressure in a fluid causes a force to act at right angles (normal) to the surface of its container 29. Recall and apply the equation: [ p = F/A ] 30. HT ONLY: Explain why the pressure at a point in a fluid increases with the height of the column of fluid above and calculate differences in pressure in a liquid by applying [ p = h ρ g ] 31. HT ONLY: Describe upthrust an object and explain why the density of the fluid has an effect on the upthrust experienced by an object submerged in it 32. HT ONLY: Explain why an object floats or sinks, with reference to its weight, volume and the upthrust it experiences 33. Describe a simple model of the Earth's atmosphere and of atmospheric pressure, explaining why atmospheric pressure varies with height above a surface 34. Define distance and displacement and explain why they are scalar or vector quantities 35. Express a displacement in terms of both the magnitude and direction 36. Explain that the speed at which a person can walk, run or cycle depends on a number of factors and recall some typical speeds for walking, running, cycling 37. Make measurements of distance and time and then calculate speeds of objects in calculating average speed for non-uniform motion 38. Explain why the speed of wind and of sound through air varies and calculate speed by recalling and applying the equation: [ s = v t ] 39. Explain the vector scalar distinction as it applies to displacement, distance, velocity and speed 40. HT ONLY: Explain qualitatively, with examples, that motion in a circle involves constant speed but changing

3 4.5.6 Forces and motion velocity 41. Represent an object moving along a straight line using a distance-time graph, describing its motion and calculating its speed from the graph's gradient 42. Draw distance time graphs from measurements and extract and interpret lines and slopes of distance time graphs, 43. Describe an object which is slowing down as having a negative acceleration and estimate the magnitude of everyday accelerations 44. Calculate the average acceleration of an object by recalling and applying the equation: [ a = Δv/t ] 45. Represent motion using velocity time graphs, finding the acceleration from its gradient and distance travelled from the area underneath 46. HT ONLY: Interpret enclosed areas in velocity time graphs to determine distance travelled (or displacement) 47. HT ONLY: Measure, when appropriate, the area under a velocity time graph by counting square 48. Apply, but not recall, the equation: [ v 2 u 2 = 2as ] 49. Draw and interpret velocity-time graphs for objects that reach terminal velocity 50. Interpret and explain the changing motion of an object in terms of the forces acting on it 51. Explain how an object falling from rest through a fluid due to gravity reaches its terminal velocity 52. Explain the motion of an object moving with a uniform velocity and identify that forces must be in effect if its velocity is changing, by stating and applying Newton s First Law 53. Define and apply Newton's second law relating to the acceleration of an object 54. Recall and apply the equation: [ F = ma ] 55. HT ONLY: Describe what inertia is and give a definition 56. HT ONLY: Estimate the speed, accelerations and forces of large vehicles involved in everyday road transport 57. Required practical 7: investigate the effect of varying the force on the acceleration of an object of constant mass, and the effect of varying the mass of an object on the acceleration 58. Apply Newton s Third Law to examples of equilibrium situations 59. Describe factors that can effect a drivers reactions time 60. Explain methods used to measure human reaction times and recall typical results 61. Interpret and evaluate measurements from simple methods to measure the different reaction times of students 62. Evaluate the effect of various factors on thinking distance based on given data 63. Estimate the distance required for an emergency stop in a vehicle over a range of typical speeds

4 4.5.7 Momentum Forces and motion Grade Next Steps 64. Interpret graphs relating speed to stopping distance for a range of vehicles 65. State typical reaction times and describe how reaction time (and therefore stopping distance) can be affected by different factors 66. Explain methods used to measure human reaction times and take, interpret and evaluate measurements of the reaction times of students 67. Explain how the braking distance of a vehicle can be affected by different factors, including implications for road safety 68. Explain how a braking force applied to the wheel does work to reduce the vehicle's kinetic energy and increases the temperature of the brakes 69. Explain and apply the idea that a greater braking force causes a larger deceleration and explain how this might be dangerous for drivers 70. HT ONLY: Estimate the forces involved in the deceleration of road vehicles 71. HT ONLY: Calculate momentum by recalling and applying the equation: [ p = mv ] 72. HT ONLY: Explain and apply the idea that, in a closed system, the total momentum before an event is equal to the total momentum after the event 73. HT ONLY: Describe examples of momentum in a collision 74. HT ONLY: Complete conservation of momentum calculations involving two objects 75. HT ONLY: Explain that when a force acts on an object that is moving, or able to move, a change in momentum occurs 76. HT ONLY: Calculate a force applied to an object, or the change in momentum it causes, by applying but not recalling the equation: [ F = m Δv / Δt ] 77. HT ONLY: Explain that an increased force delivers an increased rate of change of momentum 78. HT ONLY: Apply the idea of rate of change of momentum to explain safety features such as air bags, seat belts, helmets and cushioned surfaces Key Words (L) Newton s 3 rd Law : whenever two objects interact, the forces they exert on each other are equal, opposite and of the same type momentum: Quantity used to calculate the effects of and changes in motion of objects; momentum=mass*velocity Conservation of momentum: the total momentum of a system of objects after a collision is the same as the total momentum before the collision Reaction time: time it takes the vehicle driver to respond to danger Thinking distance: the distance the vehicle travels during the reaction time Breaking distance: distance travelled by a vehicle after the brakes have been applied before coming to a complete stop Atmospheric pressure: force per unit area produced by the weight of air; it decreases as you go higher in the atmosphere Pressure: force on a certain area Hooke s Law: law that says that a spring will extend regularly as the on it is increase -the extension is proportional to the load Spring constant: quantity that tells you how much an object will stretch by if a force is applied to it, as long as the object obeys Hooke s law Force=spring constant* extension Hydraulic system : system of liquid in pipes that can transmit force from one place to another and can also act as a force multiplier Moments: turning effect of a force moment is increased by increasing the force or the distance between a force and pivot

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