In order to get the G.C.S.E. grade you are capable of, you must make your own revision notes using your Physics notebook.

Transcription

1 In order to get the G.C.S.E. grade you are capable of, you must make your own revision notes using your Physics notebook. When summarising notes, use different colours and draw diagrams/pictures. If you do, you will find them easier to remember. Once you have made revision notes for a topic, re-visit these regularly (on the day of your examination you will not remember something you revised 4 weeks previously). Each time you re-visit a note tick the top of the page/card. This will allow you to identify any notes you have neglected. WARNING: DO NOT RELY SOLELY ON THE REVISION POWERPOINTS!

2 Click the following links to be taken to the relevant section: 1. Forces 2. Mass and Weight 3. Turning Effect 4. Centre of Gravity 5. Density 6. Kinetic Theory

3 Forces can: 1. Change the size or shape of an object. 2.Change the speed of an object. 3.Stop or start an object moving. 4.Change the direction of an object. Unit of force Newton (N). Note: Sometimes a force does not cause effects 1-4. This is because it is probably cancelling or balancing the effect of another force.

4 1. Contact Forces: The object exerting the force needs to be in contact with the object on which the force is exerted, e.g. friction, push, pull and twist. 2. Forces acting at a distance: The objects do not need to be in contact in order for the force to be exerted. a) gravitational: exists between all masses. b) Magnetic: exists between magnetic poles. Like poles will repel and unlike poles will attract. c) Electrostatic: exists between electric charges. Like charges will repel and unlike charges will attract.

5 Mass: This is a measure of how much material an object contains. Mass of an object on earth = mass of object on the moon It is measured in kilograms (kg) or grams Weight: This is a measure of the force exerted by gravity on an object. It is measured in newtons because it is a force.

6 We can find the weight of any object on Earth by multiplying its mass in kilograms by 10. weight (N) = mass (kg) x 10 Note: the mass must be in kilograms! As weight depends on the force of gravity it can change, e.g. an object in space has mass but no weight (weightless).

7 The equation for weight anywhere in the Universe is: W = mg g = gravitational field strength (this is 10 m/s 2 on Earth) W = weight in N M = mass in kg

8 Test yourself: 1. Calculate the weight of an object which has a mass of 6 kg. (click for answer) weight = mass x 10 = 6 x 10 = 60 N 2. Calculate the weight of a object whose mass is 300 g. (click for answer) W = mg = 0.3 x 10 = 3 N 3. An astronaut has a mass of 60kg a. What is his weight on Earth? (click for answer) W = mg = 60 x 10 = 600 N b. What is his mass on the Moon? (click for answer) Mass is constant mass on Moon = 60kg

9 The turning effect of a force is also called the moment of a force. It can be calculated using: moment = force x distance to pivot Force in newtons and distance in metres moment in Nm Force in newtons and distance in cm moment in Ncm

10 When a body is in equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments about the same point. Examples 1. Jack and Jill are on a see-saw. Jack weighs 750N and Jill weighs 500N. If Jack is 2m from the pivot where must Jill be if the see-saw is balanced? (click for solution) 2 m d m Clockwise moment = anticlockwise moment 750 N 500 N 500 x d = 750 x d = 1500 d = 3 m

11 2. A wheelbarrow carries a load of 500N as shown. What force must be applied to the handles in order to lift the wheelbarrow if the handles are 2m from the wheel? (click for solution) F Clockwise moment = anticlockwise moment 500 x 0.8 = F x = 2F F = 200 N 80cm 500N 2m

12 All objects have a centre of gravity. The centre of gravity is the point where all the weight of the body appears to act. The centre of gravity of the following objects is marked: Disc Rectangle Triangle Ring

13 A body will topple when the vertical line through its centre of gravity falls outside its base. (A) High C of G (B) Low C of G Object A will topple, since the vertical line through its centre of gravity falls outside the base Stability may be increased by: Increasing the base area Lowering the position of the centre of gravity Object B will not topple, since the vertical line through its centre of gravity does not fall outside its base.

14 The Density of any material is defined as the mass of unit volume of that material. Unit volume means one cm 3 or one m 3. Density is calculated using the formula: density = mass volume Remember, for a cuboid: M D x V Note: always use words when writing this equation volume = length x breadth x height

15 If the mass is in grams (g) and the volume is in cubic centimetres (cm 3 ) then the density is measured in grams per cubic centimetre (g/cm 3 ). If the mass is in kilograms (kg) and the volume in cubic metres (m 3 ) then the density is measured in kilograms per cubic metre (kg/m 3 ) To calculate density, you need to know the mass and the volume. To measure mass you use scales. To determine volume you either use the previous formula (if the object is a cuboid) or you use the methods on the next slide.

16 Irregular object that sinks: Measure volume of water (V 1 ) Measure volume of water and object (V 2 ) Calculate V 2 V 1 Irregular object that floats: Measure volume of water and heavy mass (V 1 ) Measure volume of water, heavy mass and object (V 2 ) Calculate V 2 V 1

17 Particles are: Close together high density. Held in place by strong forces. Vibrate about fixed points - solids have a fixed volume and shape. Particles: Are a little further apart than a solids - medium density. Can roll around each other liquids can flow easily. Can change their shape but have a fixed volume.

18 Particles: Are very far apart with no forces between them low density. Move around very quickly and fill all the spaces available.

19 Solids, liquids and gases are made up of atoms/molecules In solids the atoms/molecules are vibrating Heat gives them more kinetic energy This causes more vigorous vibrating When some of them overcome the bonds the solid turns to liquid As more energy is given to the liquid the remaining atoms/molecules overcome their bonds and a gas is formed.

20 Weight = mass x 10 Weight = 50 x 10 Weight = 500N Click for solution The pressure increases as the area on which he stands decreases

21 When an object is in equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments about the same point Click for solutions Centre of the wheel

22 Previous question continued clockwise moment = anticlockwise moment 780 x 40 = F x = 130F F = / 130 F = 240 N Click for solution

23 Centre of gravity Click for solutions clockwise moment = anticlockwise moment F x 8 = 8 x 10 4 x 4 8F = F = / 8 F = N

24 gravity Point where all the weight appears to act Click for solutions It is behind the plumb line

25 B Click for solutions Largest base Lowest centre of gravity

26 Volume = length x breadth x height Volume = 2 x 50 x 50 Volume = 5000 cm 3 Click for solutions Mass = Density x Volume Mass = 0.8 x 5000 Mass = 4000 g Weight = mass x 10 Weight = 4 x 10 Weight = 40 N

27 Solids, liquids and gases are made up of atoms/molecules In solids the atoms/molecules are vibrating Heat gives them more kinetic energy This causes more vigorous vibrating When some of them overcome the bonds the solid turns to liquid As more energy is given to the liquid the remaining atoms/molecules overcome Click for solutions their bonds and a gas is formed.