MOTION & REST
If an object changes its position with respect to its surroundings with time, then it is called in motion.
If an object does not change its position with respect to its surroundings with time, then it is called at rest.
Any action which causes push or pull on a body is called force. It can only be explained by describing what happens when a force is applied to an object. Force of Friction When a body slides or rolls over
another body or on a surface, then a force opposing the motion acts between those surfaces of the body which are in contact.
Types of force
When the net effect produced by a number of forces acting on a body is zero, then the forces are said to be balanced forces.
When the net effect produced by a number of forces acting on a body is non-zero, then the forces are said to be unbalanced forces.
The tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia.
1.Inertia of rest
if an object resist the change in its state of rest.
2.Inertia of motion
if an object resist the change in its state of motion.
3.Inertia of direction
if an object resist the change in its state of direction.
Newton’s First law of motion
An object remains in a state of rest or of uniform motion in a straight line unless compelled
to change that state by an applied force. This law is a law of inertia.
The momentum, p of an object is defined as the product of
its mass, m and velocity, v. That is, p = mv
The change of momentum not only determined by the magnitude of the force but also by the time during which the force is exerted.
Newton’s second law of motion
The second law of motion states that the rate of change of momentum of an object is proportional to the applied
unbalanced force in the direction of force.
while catching a fast moving cricket ball, a fielder in the ground gradually pulls his hands backwards with the moving ball.
In a high jump athletic event, the athletes are made to fall either on a cushioned bed or on a sand bed. This is to
increase the time of the athlete’s fall to stop after making the jump.
Newton’s third law of motion
when one object exerts a force on another object, the second object instantaneously exerts a force back on the first. These two forces are always equal in magnitude but opposite indirection.
When a gun is fired, it exerts a forward force on the bullet. The bullet exerts an equal and opposite
reaction force on the gun. This results in the recoil of the gun .
As the sailor jumps forward, the force on the boat moves it backwards.