Force (Physics) ICSE Class 6: Revision Notes

Revision notes for the chapter ‘Force’ in Physics subject for ICSE Class 6 students.

Question: What is the term used for push or pull.
Answer: Force

Question: Give one example each of a force as (i) a push, (ii)a pull, (iii) a stretch and (iv) a squeeze.

Answer:

• (i) Force as a push: eg. To move a pile of rubbish, it is pushed by a broom.
• (ii) Force as a pull: eg. To move a grass roller on a lawn, it is pulled by a gardener.
• (iii) Force as a stretch: eg. When a rubber string is stretched, its length increases.
• (iv) Force as a squeeze: eg. On squeezing a tube of gum or toothpaste, its shape changes.

Question: Explain the meaning of the term force.
Answer: A force is that cause which changes the state of a body (either the state of rest or the state of motion or the direction of motion) or changes the size or shape of the body.

Question: What effect can force have on a stationary body?
Answer: When force is applied on a body originally at rest, the body begins to move. For eg. A car originally at rest when pushed, begins to move.

Question: What effects can force have on a moving body.
Answer: When a force is applied on a moving body, it can have the following effects.

• (i) A force can stop a moving body.
• (ii) A force can make a moving body to move faster.
• (iii) A force can slow down a moving body.
• (iv) A force can change the direction of motion of a moving body.

Question: What effect can a force produce on a body which is not allowed to move.

Answer: When a force is applied on a body which is not allowed to move, it gets deformed, i.e., shape or size of the body changes. For example, on squeezing a piece of rubber, its shape changes, on stretching a rubber string, its length increases.

Question: Give one example each to indicate the application of a force.

Answer:

• (a) Produces motion: A ball lying on the ground moves, when it is kicked.
• (b) stops motion: A moving bicycle, bus or train is stopped by applying the brakes.
• (c) slows down motion: The speed of a moving vehicle is slowed down by applying the brakes.
• (d) changes the direction of motion: In tennis and badminton, the direction of motion of the ball or cock is changed by hitting it in the opposite direction.
• (e) deforms a body: For example, on squeezing a piece of rubber, its shape changes, on stretching a rubber string, its length increases.

Question: State the effect produced by a force in the following cases.

Answer:

• (a) The sling of a rubber catapult is stretched: On stretching, the shape and size of the rubber catapult changes i.e. its length increases.
• (b) A man pushes a heavy cart: The heavy cart begins to move.
• (c) A player uses his stick to deflect the ball: The direction of the ball changes.
• (d) A cyclist applies brakes: The speed of the moving cycle is slowed down by applying the brakes.
• (e) A spring is compressed: There is a change in shape and size of the spring, its length decreases.

Question: Name two kinds of force in nature.

Answer: Depending upon the application of forces, they are classified in two categories: Contact forces and Non-contact forces.

Question: Name the type of force which acts in the following cases:

Answer:

• (a) A coolie lifts a luggage – Muscular force
• (b) A bicycle comes to rest slowly when the cyclists stops pedalling – Frictional force
• (c) A stone falls from a roof – Gravitational force
• (d) A comb is rubbed with silk attracts bits of paper – Electrostatic force
• (e) A string hangs with a load – Force of tension
• (f) A horse moves a cart – Muscular force
• (g) A magnet attracts an iron pin – Magnetic force
• (h) A boy opens a door – Muscular force
• (i) An apple falls from a tree – Gravitational force
• (j) A man rows a boat – Muscular Force

Question: What do you mean by gravitational force? Give an example to illustrate it.
Answer: Gravitational force of attraction between any two bodies at a distance, such as the force of attraction between two heavenly bodies, the force of attraction on a body by earth, etc. Eg. The leaves and fruits fall from a tree downwards towards the ground due to gravity.

Question: Define the term “weight of a body”.
Answer: The weight of a body is the force by which earth attracts that body, so the weight is also called its force due to gravity.

Question: What do you understand by the term friction?
Answer: Friction is the force that opposes the relative motion between the two surfaces in contact with each other.