2. 1© Manhattan Press (H.K.) Ltd. Describing a force Nature of force Nature of force 1.1 Force

3. 2 © Manhattan Press (H.K.) Ltd. Statics 1.1 Force (SB p. 38) MechanicsStudy StaticsBodies at rest KinematicsBodies in motion without concerning the cause of motion DynamicsRelationship between motion and the forces that cause it

4. 3 © Manhattan Press (H.K.) Ltd. Force A. Describing a force 1.1 Force (SB p. 39) Force – vector Unit – newton (N)

5. 4 © Manhattan Press (H.K.) Ltd. Force A. Describing a force 1.1 Force (SB p. 39) A force is described by specifying: (a) its magnitude and direction, (b) the body on which it acts, and which part of the body it acts, (c) the body that exerts the force, and (d) the nature of force.

6. 5 © Manhattan Press (H.K.) Ltd. Force A. Describing a force 1.1 Force (SB p. 39) e.g. weight = 600 N a 600 N pointing towards the earth’s centre acted on the man by the earth gravitational force

7. 6 © Manhattan Press (H.K.) Ltd. Nature of force Four types of forces in nature 1.1 Force (SB p. 39) ForcePropertyRelative strength Gravitational force (F g ) 1. Long- range attractive force exists among massive particles in the Universe 2. It is very small, but it is not negligible if at least one of the bodies is massive. 1 Go to More to Know 1 More to Know 1

8. 7 © Manhattan Press (H.K.) Ltd. Nature of force Four types of forces in nature 1.1 Force (SB p. 39) ForcePropertyRelative strength Electromagnetic force (F e ) Long-range attractive (or repulsive) force exists among charged particles. 10 40 Go to More to Know 2 More to Know 2

9. 8 © Manhattan Press (H.K.) Ltd. Nature of force Four types of forces in nature 1.1 Force (SB p. 39) ForcePropertyRelative strength Weak nuclear force Short-range attractive force exists among sub-atomic particles 10 30 Strong nuclear force Short-range attractive force exists among nucleons 10 42 Go to More to Know 3 More to Know 3

10. 9 © Manhattan Press (H.K.) Ltd. End

11. 10 © Manhattan Press (H.K.) Ltd. Different gravitational forces The gravitational forces for the same mass on different planets are different. Do you know that what is your weight on the moon? It is 1/6 that on the earth. Return to Text 1.1 Force (SB p. 39)

12. 11 © Manhattan Press (H.K.) Ltd. Electromagnetic force Most forces that we come across in daily life such as friction and tension are actually examples of electromagnetic force. Return to Text 1.1 Force (SB p. 39)

13. 12 © Manhattan Press (H.K.) Ltd. Weak nuclear force Weak nuclear force takes part in the radioactive decay of atoms. Return to Text 1.1 Force (SB p. 39)