Science : Force (Part-1)

What is force?

Force is a push or a pull on an object.

It changes or tends to change the state or shape of an object.

  • I. Unit is Newton (N)
  • It is a vector quantity
  • Whenever we are pushing, pulling, lifting bending, twisting, tearing we are exerting a force.

Force can –

  • Make a stationary body move.
  • Change the speed of a body.
  • Change the direction of motion of a body
  • Change the size or shape of the body

Here are some important forces which you are familiar with –

  • Gravitational force – Force due to gravitational pull.

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  • Frictional force – Force which opposes motion.

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  • Electrical force – Force of attraction or repulsion between electrical charges.

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  • Magnetic force – Force of attraction or repulsion between the poles of magnets.

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  • Contact force – Force of repulsion when two objects are pressed together.

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Questions asked in previous years.

Q.1       Which of the following force is a virtual force?

(a) Frictional force

(b) Centripetal force

(c) Centrifugal force

(d) Nuclear force

Ans. (a)  Centrifugal force is an inertial force that is acted upon a body moving on a circular path.

  • It acts outwards from the centre of rotation.

Q.2       Water drops cannot stick to the oily surface due to –

(a) Atmospheric pressure

(b) Viscosity of water

(c) Lack of adhesive force

(d) Surface tension

Ans. (c) Water drops cannot stick to the oily surface due to lack of adhesive force.

Adhesive force – Adhesive forces are the attractive forces between different molecules.

Q.3       Ball pen functions on the principal of –

(a) Viscosity

(b) Boyle’s law

(c) Gravitational force

(d) Surface tension

Ans.(d) Ball pen works surface tension

Surface tension:- The force that causes the molecules on the surface of a liquid to be bound together and form a layers.

Q.4       Upward force on a floating body is called –

(a) Buoyancy                (b) Jerk                         (c) Gravitational            (d) Floatation

Ans. (a) Buoyancy force acts upon an object that is floating on a fluid.

Q.5       Which contact force is responsible for changing the state of motion of an object?

(a) Magnetic force

(b) Frictional Force

(c) Electrical force

(d) electro-Magnetic Force

Ans. (b)   Frictional force is responsible for changing the state of motion of an object.





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