Force

Question 1

What is linear motion

Answer 1

When a force acts on a stationary rigid object which is free to move the body starts moving in a straight path in the direction of the force

Eg = a ball moving on the floor

Question 2

What is rotational motion

Answer 2

Rotational motion can be defined as a motion of an object around a circular path, in a fixed orbit.

Eg = if a wheel is pivoted at its centre and a force is applied the wheel rotates about its center

Question 3

What is the turning effect of the force

Answer 3

The turning effect on the body about an axis is due to the moment of force applied on the body

Question 4

What are the Factors affecting turning effect of the body

Answer 4

—> magnitude of force applied

—> perpendicular distance of line of action of force applied on the body

Question 5

What is torque (moment of force )

Answer 5

Torque is equal to the product of magnitude of the force and the perpendicular distance of line of action of the force from the axis of rotation

Torque = force x perpendicular distance from midpoint

Question 6

What is SIunit of torque

Answer 6

Nm (Newton meter)

Question 7

Relation between Nm and dyne cm

Answer 7

1 nm = 10^7 dyne cm

Question 8

Define couple

Answer 8

–> couple is a pair of forces,

–> 2 equal and opposite parallel forces

–> displaced by perpendicular distance or moment

–> a couple is always needed to produce a rotation

Question 9

Formula for couple

Answer 9

Moment of couple = either force x perpendicular distance between 2 forces

Question 10

Define equilibrium of bodies

Answer 10

When a number of forces acting on a body produce no change in its state of rest or of linear or rotational motion, the body is said to be in a state of equilibrium

Question 11

What are the 2 kinds of equilibrium

Answer 11

—> static equilibrium

—> dynamic equilibrium

Question 12

Define static equilibrium and give example

Answer 12

When a body remains in a state of rest under the influence of several forces, the body is in static equilibrium

Example = if a book is lying on a table the weight of the book exerted on a table vertically downwards is balanced by an equal and opposite force of reaction exerted by the table on the book vertically upwards

Question 13

Define dynamic equilibrium and give example

Answer 13

When a body remains in the same state of motion, under the influence of several forces the body is said to be In dynamic equilibrium

Example = an aeroplane moves at a constant height when upward lift on it balances its weight downwards

Question 14

Conditions for equilibrium

Answer 14

—> the resultant of all forces acting on the body should be zero

—> the algebraic sum of moments of all forces acting on the body about the point of rotation should be zero

Question 15

What is the principal of moments

Answer 15

If the algebraic sum of moments of all the forces acting on the body, about the axis of rotation is zero, the body is in equilibrium

Sum of clockwise moments = sum of anti clockwise moments

Question 16

Centre of gravity definition

Answer 16

The centre of gravity of a body is the point about which the algebraic sum of moments of weights of all particles constituting the body is zero.

The entire weight of the body can be considered to act at this point, how so ever the body Is placed

Question 17

define uniform circular motion

Answer 17

when a particle moves with a constant speed in a ciruclar path, its motion is said to be uniform circular motion

Question 18

define centripetal force

Answer 18

it is the force acting on a body moving in a circular path, in a direction towards the centre of the circular path

Question 19

example of centripetal force

Answer 19

–> in an atom the electron revolves around the nucleus in a circular path for which the required centripetal force is obtained form the electrostatic forces of attraction on the negatively charged electron by the positively charged nucleus

Question 20

define centrifugal force

Answer 20

a force assumed to be acting on the body in a direction away from the centre of circular path is called centrifugal force

Question 21

example of centrifugal force

Answer 21

–> Mud flying of a tire is one example of the centrifugal force.

Question 22

what type of force is centrifugal force

Answer 22

it is a fictitious force

the only real force is the force of tension acting towards the centre