Chapter 5 Laws Of Motion
FIRST LAW OF MOTION
Every body continues to be in its state of rest or uniform motion in a straight line unless compelled by some external force to act otherwise.
The first law of motion can be simply expressed as:
“If the net external force on a body is zero, its acceleration is zero. Acceleration can be non-zero only if there is a net external force on the body.”
Momentum (P) of a body is defined to be the product of its mass (m) and velocity (v) and is denoted by p.
p = mv
Momentum is a vector.
SECOND LAW OF MOTON
“The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts.”
The product of force and time is the change in momentum. The change in momentum is known as impulse.
Impulse = Force x time interval = change in momentum
THIRD LAW OF MOTION
“To every action, there is an equal and opposite reaction.”
CONSERVATION OF MOMENTUM
In an isolation system (i.e. a system with no external force), mutual forces between pairs of particles in the system cause momentum change in individual particles, but since the mutual forces for each pair equal and opposite, the momentum changes cancel in pairs and the total momentum remains unchanged. This is known as the Law of conservation of momentum i.e. the total momentum of an isolated system of interacting particles is conserved.
EQUILIBRIUM OF A PARTICLE
Equilibrium of a particle in mechanics refers to the situation when the net external force on the particle is zero.