Force
ICSE Class 6 · Physics · Chapter 3
What this chapter covers
- Force as a push or a pull
- Effects of force
- Force of friction
- Advantages and disadvantages of friction
Key points
- A force is a push or a pull on an object.
- A force acts between two things, and you can see only its effects.
- A force can make an object at rest move, and stop a moving object.
- A force can change the speed and the direction of a moving object.
- A force can change the shape and size of an object.
- A force does not change the mass of an object.
- Friction is a force between two surfaces in contact that opposes motion.
- Rough surfaces have more friction than smooth surfaces.
- Static friction is the largest, sliding friction is less, and rolling friction is the smallest.
- Friction helps us walk, hold things, write and stop vehicles.
- Friction wears things out, produces heat and makes work harder.
- Oil, grease, powder and wheels reduce friction; grooves, sand and chalk increase it.
Questions answered
What is a force?
A force is a push or a pull on an object.
Say whether each action is a push or a pull: (a) opening a drawer, (b) kicking a ball, (c) lifting a school bag.
(a) pull, (b) push, (c) pull.
A batsman hits the ball towards the boundary. Name two effects of the force from the bat.
The force changes the direction of the ball, and it also changes its speed.
You squeeze a sponge in your hand. Which two things about the sponge change, and which one does not?
Its shape and size change. Its mass does not change.
A clay ball of 150 g is rolled into a long snake shape. What is the mass of the snake?
150 g, because a force changes shape but not mass.
Why does a marble rolling on the floor stop by itself after some time?
Friction between the marble and the floor acts against its motion and slowly stops it.
Name the type of friction in each case: (a) a heavy box that will not move when pushed, (b) a child going down a slide, (c) a trolley moving on wheels.
(a) static friction, (b) sliding friction, (c) rolling friction.
Give one advantage and one disadvantage of friction.
Advantage: friction lets you walk without slipping. Disadvantage: friction wears out the soles of shoes and the tyres of bicycles.