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 Reduce 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