Common forces in mechanics and circular
Force :
The external agency which changes (or) tries to change the state of body is known as force.
SI unit of force: kg ms-2 or N
MKS unit of force: Kg wt.
CGS unit of force: dyne
1 newton = 105dyne
1 kg wt = 9.8 newton = g newton
Basic forces in nature:
The basic forces in nature are:
(1) Gravitational force
(2) Electromagnetic force
(3) Strong nuclear force
(4) Weak nuclear force
Impulsive force and impulse:
Impulsive force:
The force which acts on a body for a short time interval is called impulsive force.
Examples:
1. A bat hitting the ball.
2. The collision of two billiard balls.
3. The firing of a gun.
Impulse:
Impulse is equal to change in momentum
Impulse = m v – mu
Impulse = F x t
The area under force-time graph gives impulse.
To decrease an impulsive force, time of impulse is increased
Example:
Shock absorbers used in motor cycles and cars.
Explanation:
When the vehicles move over an uneven road, it receives a jerk. So the vehicle receives the impulsive force. To minimize this impact shock absorbers are used.
The shock absorbers increase the time of the jerk, thereby reducing the impulsive force.
This minimizes the damage to the vehicles.
Example Problem 3:
A batsman hits back a ball straight in the direction of the bowler without changing its initial speed of 12ms-1. If the mass of the ball is 0.15kg. Determine the impulse imparted to the ball.
- A) Impulse = Change in momentum
P= mv – (-mu) = mv + mu = 2mu ( v=u)
P = 2 x 0.15 x 12 = 3.6Ns