NCERT 5th Class (CBSE) Science: Force and Energy – Simple Machine

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Question: List any two advantages and two disadvantages of friction?

Answer: The two advantages of friction are –

1. The friction between the types of vehicle and the road makes them role forward. This friction makes as movement of vehicles possible.
2. Friction between chalk and the black board makes it possible for the teachers to write on the blackboard.

The two disadvantages of friction are –

1. Friction makes it hard to slide heavy objects across the floor.
2. Friction generates heat. Heat produced due to friction causes damage to machine parts like car brakes.

Question: What is a lever? Describe its three types with examples.

Answer: A lever is a rigid rod arranged in such a manner that it can move freely around a fixed point. It consists of the following three parts.

1. Fulcrum – This is the fixed point around which the rod moves.
2. Load – It is the object on which work is to be performed.
3. Effort – It is the force that needs to be applied on the rod in order to the perform a task.

Firs – Class lever:

Levers in which the fulcrum is located between the load and effort are called first class or class one levers.

Eg. – a pair of scissors, a seesaw and a crowbar.

Second – Class lever:

Levers in which the load is located between the fulcrum and the effort are called second-class or class two levers.

Eg. – a wheelbarrow, a bottle opener and a nut cracker.

Third – class lever:

Levers in which the effort is located between the fulcrum and the load are called third – class three levers.

Eg. – Stapler, forceps, fishing rods and ice tongs or chimta.