Study Materials

# NCERT Solutions for Class 8th Science

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## Chapter 11. Force And Pressure

Ques: Define force.

Ans: A push or a pull on an object is called a force.

Ques: Define muscular force.

Ans: The force resulting due to the action of muscles is known as the muscular force.

Ques: Write the kinds of force.

Ans: There are two kinds of force.

(i) Contact force

(ii) Non-contact force

Ques: What is contact force? Write its types.

Ans: Muscular force can be applied only when it is in contact with an object, it is also called a contact force.

This is two types.

(i) Muscular force – The force resulting due to the action of muscles is known as the muscular force.

(ii) Frictional force  -  The force acts opposite to the direction of motion and this is responsible for changing the state of motion of objects. It arises due to contact between the surfaces.

Ques: Why is frictional force known as contact force?

Ans: The frictional force known as contact force as it arises due to contact between the surfaces.

Ques: What is non-contact force? Write its types.

Ans: The force which is felt by the objects without any contact is known as non-contact force.

This is two types.

(i) Electrostatic force – The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

(ii) Gravitational force – Every object attracts each other and pulls toward itself. Such force which applied on objects is known as Gravitational force and gravitation

Ques: Define Pressure.

Ans: The force acting on a unit area of a surface is called pressure

Force                                                                                 Pressure  =

Area on which it acts

Ques: Why shoulder bags are provided with broad straps and not thin strap?

Ans: Broad straps reduce pressure on back. If the strap will be thin the value of pressure will be raised as per unit area of surface gets reduced.

Ques: Why have nails sharp edges?

Ans: Nails have sharp edge because if per unit area of surface is reduced the pressure on it is increased. Hence nails push easily.

Ques: What is atmosphere ?

Ans: Envelop of air is known as the atmosphere.

Ques: What is atmospheric pressure?

Ans: The pressure exerted by this air is known as atmospheric pressure.

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