1. Mr. Lajos Papp The British International School, Budapest 2010/2011

2. UNITS Kilogramkg Metrem Metre/secondm/s Metre/second 2 m/s 2 NewtonN Seconds

3. MOVEMENT AND POSITION

4. Distance is a measure of how far an object has travelled, or how far away it is. Speed is a measure of how fast an object is moving. It is measured in metres per second (m/s). Speed = distance ÷ time. If an object is stationary (not moving), then its speed is zero. Velocity is similar to speed. It is a measure of how fast an object is moving, and is measured in m/s. Velocity = distance ÷ time.

5. The difference between velocity and speed is that velocity is speed in a certain direction. If an object is moving in a straight line, then its speed and velocity will be the same. If the moving object stays at the same speed but changes direction, then we say that the velocity has changed (because the direction has changed) but the speed has stayed the same.

6. If an objects velocity does not change, we say it has a constant velocity. When an objects velocity changes, it is called acceleration. Acceleration = change in velocity ÷ time. This equation is written as a = (v-u) ÷ t a = acceleration v = final velocity (the one it ended up with) u = initial velocity (the one it started with) t = time

7. The unit of acceleration is m/s 2. If an object gets faster, it has a positive acceleration. If an object gets slower, it has a negative acceleration.

8. 1. If a car changes from 10 m/s to 30 m/s in 8 seconds, what is its acceleration? v = 30 m/s u = 10 m/s t = 8 s a = (30 - 10) ÷ 8 = 20 ÷ 8 = 2.5 m/s 2

9. 2. If a bicycle moving at 15 m/s takes 10 seconds to stop, what is its acceleration? v = 0 m/s u = 15 m/s t = 10 s a = (0 - 15) ÷ 10 = -15 ÷ 10 = -1.5 m/s 2

10. The acceleration is negative because the bicycle has slowed down. The object is said to have constant acceleration if it gets faster (or slower, or its direction changes) at the same rate.

11. The graph shows an object which is not moving. Its distance stays the same as time goes by.

12. The graph shows that the objects distance increases as time goes by. The object is moving. The straight line shows it is a constant velocity. The slope of the line shows how fast the object is going.

13. The graph shows an object moving with constant velocity. The object is moving in the opposite direction The slope of the line shows how fast the object is moving.

14. The curve in the graph shows that an objects velocity is changing as time goes by.

16. In region A the object is moving with constant velocity. In region B the object is at rest. In region C the object is again moving with constant velocity but compared with region A (i) the object is moving more slowly because the slope is less steep. (ii) the object is moving in the opposite direction because distance is decreasing as time goes by.

22. In region A the object is moving with constant acceleration. In region B the object is moving with constant velocity. In region C the object is again moving with constant acceleration but compared with region A (i) the acceleration is slower because the slope is less steep (ii) the acceleration is negative because the slope is downwards. The total distance travelled by the object can be calculated by measuring the area under the graph.

24. The area under the graph can be divided into two triangles and one rectangle. The area of triangle A= 0.5 x 10 x 20 = 100 The area of triangle C = 0.5 x (70 - 30) x 20 = 400 The area of rectangle B= (30 - 10) x 20 = 400 The distance travelled is the total area = A + B + C = 100 + 400 + 400 = 900 m.

25. FORCES, MOVEMENT AND SHAPE

26. A force is a push or a pull. It is measured in Newtons (N). Various types of force Gravitational: always attracts Electrostatic: attracts, repels Magnetic: attracts, repels

27. If all the forces which act on an object along the same line are equal and opposite, the forces are called balanced. Newton's first law says that if the forces on an object are balanced then it will carry on as it is. This means that (i) if the object is not moving then it will continue to stay still. (ii) if the object is already moving then it will continue to move with a constant velocity.

29. Part (ii) goes against common sense. We know that in the "real world" things slow down and stop if there is nothing to keep them going. Newton understood that there is a force which makes things slow down and stop. It is called friction. Friction is an opposing force. It acts in the opposite direction to a force which is applied to an object.

30. Friction occurs where two solid objects rub against each other, or where a liquid or gas is pushed out of the way of a moving object. For two solid objects, the amount of friction depends on how well the surfaces grip each other. Tyres on a road have very high friction (they don't slip), skates on ice have very low friction (they slip easily). For a solid object moving through a liquid or gas, the amount of friction depends on the shape and surface area of the object and the viscosity (thickness or thinness) of the liquid.

31. For an object moving through air, friction is called "air resistance" or "drag". A parachute will have a very high air resistance, a missile will have a very low air resistance. An object moving through a high viscosity liquid (syrup) will have high friction (drag), an object moving through a low viscosity liquid (water) will have a low friction (drag). Is friction good or bad?

32. Newton's second law: that if the forces on an object are unbalanced then its motion will change. The bigger the force, the bigger the change in motion. A change in motion is called acceleration. Newton's second law gives rise to the equation: F = m x a (force N = mass kg x acceleration m/s 2 ) Forces which act along a straight line can be added if the forces are in the same direction, or subtracted if the forces are in the opposite direction.

33. A stationary rocket was moving at 240 m/s 2 minutes after take off. What was its acceleration? Use a = (v-u) ÷ t v = 240 m/su = 0 m/s (because the rocket was stationary) t = 2 mins (changing minutes into seconds) = 120 s a = (240 - 0) ÷ (120) = 240 ÷ 120 = 2.0 m/s 2

34. The rocket has a mass of 1500 kg. What force was needed to give it the acceleration of 2.0 m/s 2 ? Use F = m x a F = 1500 kg x 2 m/s 2 = 3000 N

35. Mass is an amount of substance. It is measured in kilograms. It tells you how many particles (atoms, ions or molecules) you have, not what they weigh. Gravity is a force of attraction between masses. Gravity is a property of mass, the bigger the mass, the bigger the gravity. The further away from each other the masses are, the weaker the gravity between them.

36. On Earth the force of gravity is 10 N/kg. The acceleration due to gravity (how fast things accelerate when you drop them) is 10 m/s 2. Weight is the force of gravity pulling on a mass. Weight is a force, and so it is measured in Newtons, not kilograms. Weight = mass x gravity W = m x g Compare this with the general formula F = m x a. Weight is the force, gravity is the acceleration.

37. If you go to the shops, you will find fruit and vegetables weighed in kilograms. In physics, this would be considered to be wrong. On Earth the force of gravity is 10 N/kg, so you can convert mass into weight by multiplying it by 10. For example, 1kg of tomatoes weighs 10 N. If you took your 1kg of tomatoes to the moon, you would still have the same mass (the same number of tomatoes) but they would weigh less because the moon has less gravity than the Earth.

38. Cone falling from a cliff Weight is the force pulling the cone downwards, air resistance (drag) is the force pushing the cone upwards. When the cone first falls, there is a force from the weight of the cone but very little drag because the cone is moving slowly and air resistance is small. The forces are unbalanced (large downward force, small upward force) and so the cone has a large acceleration in the direction of the larger force (downwards).

39. As the cone gets faster, the drag increases and acceleration decreases until the weight and drag are equal in size. Now the forces are balanced and the cone will continue to fall with a constant velocity called its terminal velocity (this is as fast as the falling object can go).

41. The motion of the cone is shown on the velocity - time graph below.

42. A cone falls from a cliff, how fast will it be moving after 3 seconds? Use a = (v-u) ÷ t a = 10 m/s 2 because of gravity. u = 0 m/s (initial downward velocity). t = 3 s v = 30 m/s In reality, the velocity will be a little less than this because air resistance (friction, drag) will slow the cone down.

43. You may have noticed that the above calculation takes no account of the mass of the cone. All things fall with the same acceleration, so if both a penny and a cone were thrown from a cliff at the same time, they would both hit the ground at the same time. Things will fall noticeably slower if (i) their density is close to the density of air (for example a feather) (ii) they have a large air resistance in proportion to their weight (for example a parachute).

44. The stopping distance of a car The total distance which is needed to stop a moving car can be divided into two parts. 1. The thinking distance is how far the car travels between the moment when the driver first realizes that the car must be stopped and the moment when they apply the brakes (reaction time). Thinking distance is increased if the reaction time of the driver gets slower because of tiredness, alcohol (or other drugs) or distractions. The faster the car is travelling, the further it moves during the thinking distance.

45. Thinking distance can be reduced by using road signs to warn the driver that they might have to stop soon. The more alert a driver is, the quicker they can apply the brakes and the smaller is the thinking distance. 2. The braking distance The braking distance is the minimum distance in which a car can stop once the brakes are put on. The stopping distance = thinking distance + braking distance.

46. The braking distance is affected by 1. Speed The braking distance of a car increases as the speed increases. 2. Mass The braking distance of a car increases as the mass increases.

47. 3. Road conditions (friction) The most important friction occurs between the tyres and the road surface. If the road is wet or icy, then friction is reduced and the car will take longer to stop or the tyres will slip (skid).

48. Turning forces Two masses on a see-saw. What force acts on the masses? Which way will the see-saw go? pivotgravity The see-saw turns around the pivot. What factors effect the size of a turning force?

49. Moments The size of the turning force or moment depends upon: 1.The distance of the force from the pivot. 2.The size of the force. Moment = Force x perpendicular distance from pivot Moments measured in Newton metres (Nm) Force measured in Newtons (N) Distance measured in metres (m)

50. Principle of moments Anticlockwise moments = Clockwise moments Where should a force of 50N be positioned to balance the see-saw? Anti-clockwise moments = 25 N x 2 m = 50 Nm Clockwise moments = 50 N x ? m Anti-clockwise moments = Clockwise moments 50 Nm= 50 N x ? M distance= 1 m 25N 2 m1 m 50N

51. Principle of moments Drag and drop any of the masses onto the “see – saw” and try to get it to balance. The masses are in kilograms and the distance in metres.

52. Moments questions 1.Where should a force of 60N be positioned to balance the ruler below? 2.What size force should be positioned on the left to balance the ruler shown? 15N 4 m1 m 60N 15N 4 m1 m ? NForce = 60 N

53. The weight of a body acts through its centre of gravity.

54. Helical springs

55. Hooke’s law Hooke's law states:- the extension is proportional to the force and the spring will go back to its original length when the force is removed as long as we don't exceed the elastic limit.

57. Wire and elastic Different materials react differently when a force is applied to them.

58. Wire and elastic If a material obeys Hooke's Law, its extension is proportional to the applied force. If the force is removed, the material returns to its original length. Springs and metal wire obey Hooke's law up to the elastic limit. Beyond this point, they are permanently deformed. They will not return to its original length when the force is removed. copper rubber F F e e

59. Elastic limit Below the elastic limit, the spring is showing "elastic behaviour": the extension is proportional to the force, and it'll go back to its original length when we remove the force. Beyond the elastic limit, we say that it shows "plastic behaviour". This means that when a force is applied to deform the shape, it stays deformed when the force is removed. Elastic limit Elastic behaviour Plastic behaviour

60. Extension = present length – original length Diagram The apparatus is set up as shown. For the purposes of this experiment we shall be using loads of 100g, and the extension of the spring shall be measured in metres.

61. Method: What is the independent variable? (range?) What is the dependent variable? ( How will this be measured accurately?) What are the control variables? Table: single spring Equilibrium length __________m Total Hanging Mass (g) Total Hanging Mass (kg) Total force (mg) g= 10 N/kg Stretched length (m) Extension (m) 100 200 300 400 500 600 700 800 900 1000 1600

62. Graph: Plot a graph of force against extension. Conclusion: Comment on the shape of the best fit line, try to describe the pattern which appears. Have you found any simple rule for springs? What happened to the stretch when you doubled the load? And three times? Can you work out the gradient? What does this gradient mean? What happens when large loads are added to the spring? How would the plot look if you replaced the spring with a stiffer spring? weaker spring? Force (N) Extension (m)

63. Hooke’s Law "Hooke's Law" is about stretching springs and wires. Hooke's Law states:- the extension is proportional to the force the spring will go back to its original length when the force is removed so long as we don't exceed the elastic limit.

64. Our solar system is the name given to the Sun and the planets which orbit it. The Sun is a star. There are eight planets (plus Pluto) and many asteroids which orbit the Sun. Some of the planets have moons. The way in which all the planets and moons move is governed by the force of gravity. There are a very large number of solar systems in the Universe. Some of the planets in these other solar systems may support life. Between the planets, stars and galaxies of the Universe lies the vacuum of space. A vacuum is the absence of all substance. Space is not a perfect vacuum but the substance which does exist is very thinly spread.

76. P = V x I. Power = Voltage x Current. V = I x R. Voltage = Current x Resistance. Q = I x t. Charge = Current x time. E = V x Q. Energy = Voltage x Charge. GPE = mgh. Gravitational Potential Energy = mass x gravity x height. KE = ½mv 2. Kinetic Energy = 0.5 x mass x velocity 2. W = F x d. Work done = force x distance. W = E. Work done = energy transferred. s = d ÷ t. speed = distance ÷ time. a = (v-u) ÷ t. acceleration = change in velocity ÷ time. F = m x a. Force = mass x acceleration. w = m x g. weight = mass x gravity. p = F ÷ a. pressure = force ÷ area. d = m ÷ v. density = mass ÷ volume. v = f x l. wave speed = frequency x wavelength.