Force & its Types, Friction- Types & use

Force & its types. Contact & Non-contact force, Friction - effects, advantages & disadvantages
Use of friction in daily life. Force a necessary evil

1. Force

2. Force Examples of Force. What are the effects of Force?

3. Effects of Force Move objects Stop objects Speed up objects

4. Effects of Force Slow down objects Change direction of object Change shape of object

5. Definition of Force A force changes the state of a body ( state of rest, state of motion, direction of motion) or changes the size and shape of the body.

6. Types of Forces Contact Force: (contact made) Non – Contact Force: ( no contact made)

7. Non – Contact Force Gravitational Force : Earth attracts all objects towards it

8. Non- Contact Force Electrostatic Force: Force of attraction developed by rubbing certain objects against another object.

9. Non – Contact Force Magnetic Force: A magnet attracts iron articles without contact

10. Contact Force Muscular Force Force which acts on bodies by making an actual contact.

11. Contact Force (Tension) Tension force : It stretches materials

12. Contact Force (Force of Reaction) An object kept on a surface gives a reactional force. Reactional Force – perpendicular / opposite to surface of body exerting force.

13. Contact Force (Friction) Friction: - Friction is a force - Opposes the motion between the two surfaces - in contact with each other. Direction of motion  Direction of Friction by road

14. Effects of Friction Stops moving objects Acts opposite to direction of motion Produces heat Wear and tear of surface

15. Factors affecting Friction Smoothness of surface Weight of the object Nature of medium in which body moves

16. Types of Friction Static Friction Force acting between two surfaces preventing movement or sliding of objects Sliding / Kinetic Friction Force applied by surface on object in motion Rolling Friction Force opposing rolling motion of objects Static Friction > Sliding Friction > Rolling Friction Static Friction: Prevents objects from moving Sliding Friction: Causes sliding objects to stop Rolling Friction: Causes rolling objects to stop

17. Recap: Which friction is in place here? Static Friction Sliding Friction Rolling Friction

18. What is the correct order ? Static Friction > Sliding Friction > Rolling Friction Rolling Friction > Sliding Friction > Static Friction Sliding Friction > Static Friction > Rolling Friction Static Friction > Rolling Friction > Sliding Friction

19. Disadvantages of Friction More force is needed to move objects – more energy is spent Causes wear and tear - soles of shoes / tires / wheels get worn out. Produces heat – rubbing of machine parts cause sparks

20. Ways to R educe Friction Making surface smooth Using lubricants Using Ball bearings Streamlining objects

21. Advantages of Friction Able to hold things Can Walk without slipping Tire gets grip on the road (no skidding) Lighting matchstick on matchbox Writing on board with chalk Stopping vehicles

22. Making surfaces rough Using dry surfaces Increasing the weight Ways to Increase Friction Good grip with rough surface Driving is safe on dry roads Sand beach cars use heavy tires