Newton’s First Law
Every object continues in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state. This law states that if there is no resultant force acting on an object on rest, the object will remain at rest; and if there is no resultant force acting on an moving object, the moving object will continue to move at a constant speed in a straight line i.e. constant velocity. Newton’s first law describes the behaviour of objects when there is no resultant force acting on them.
Newton’s Second Law
When a resultant force acts on an object of constant mass, an acceleration will result with the product of its mass and acceleration equal to the resultant force, the direction of acceleration being in the same direction as that of the resultant force. This law states that when there is a resultant force acting on an object, the object will either decelerate or accelerate.
F = ma, where F = resultant force
m = mass of the object
a = acceleration of the object
Newton’s Third Law
If body A exerts a force F on body B, then body B exerts a force of -F (of equal size but in opposite direction) on body A.
Newton’s third law states that forces always occur in pairs. These forces are called action force and reaction force. These forces are equal in magnitude and they act opposite to each other. They act on different bodies.