1. AQUINAS DIOCESAN GRAMMAR FORCES Double Award - Physics

2. AQUINAS DIOCESAN GRAMMAR What is a force? A force is a PUSH or a PULL

3. AQUINAS DIOCESAN GRAMMAR What can forces do? Forces can – Change the speed of an object. Change the direction of movement of an object. Change the size or shape of an object.

4. AQUINAS DIOCESAN GRAMMAR Examples of Forces Weight is a very common force Tension. Resistance. – Air resistance, drag. Frictional forces try to stop thing moving.

5. AQUINAS DIOCESAN GRAMMAR Examples of Forces contd. Contact forces are produced when 2 objects are pushed together. Magnetic forces act between magnetic materials Electrical forces between electric charges

6. AQUINAS DIOCESAN GRAMMAR

7. Measuring Forces Force is measured in newtons (N) 1newton = 1N

8. AQUINAS DIOCESAN GRAMMAR Measuring Force The weight of an object can be measured using a spring balance.

9. AQUINAS DIOCESAN GRAMMAR WEIGHT – THE PULL OF GRAVITY The pull of the earth on an object is called its weight. The pull or weight is caused by what we call ‘gravity’.

10. AQUINAS DIOCESAN GRAMMAR Force of Attraction Force of attraction between all mass. Size of the forces decreases with distance.

11. AQUINAS DIOCESAN GRAMMAR Force of Attraction F = G m 1 m 2 r2r2 The gravitational force F (N) between two particles m 1 (kg) and m 2 (kg) placed distance r (m) apart is given by Where G is the universal gravitational constant and has value 6.7 x 10 -11 Nm 2 kg -2

12. AQUINAS DIOCESAN GRAMMAR The weight of a body is the force of attraction between the mass of the body and the mass of the Earth. The direction of this force is always to the centre of the earth while the size of the force is given by the formula. Weight = mass x pull of gravity W=mg

13. AQUINAS DIOCESAN GRAMMAR Mass The mass of an object is a measure of the amount of matter (or stuff) in it.

14. AQUINAS DIOCESAN GRAMMAR MASS depends on - The number of atoms it contains. The size of those atoms. The unit of mass is the kilogramme (kg)

15. AQUINAS DIOCESAN GRAMMAR W = mg At the surface of the earth: W = m x 9.8N/kg Or roughly W = m x 10N/kg

16. AQUINAS DIOCESAN GRAMMAR For example: the weight of a girl of mass 35kg is given by W = 35 x 10N/kg = 350N

17. AQUINAS DIOCESAN GRAMMAR How much would a 1kg mass weigh on the Moon, if the pull of gravity there is about one- sixth of the pull of gravity here? W moon = 1 x (10  6) = 1.67N