Answer:
According to Newton's
first law of motion, a body at rest or in uniform motion will remain at rest or
in uniform motion unless an unbalanced force acts upon it. This law consists of
three parts:
(a) The first part
says that a body at rest continues in its state of rest. For instance, a boy
standing in a train falls backward when the train suddenly starts moving
forward. This is because when the bus moves, the lower part of his body begins
to move along with the train while the upper part of his body continues to
remain at rest due to inertia.
(ii) The
second part says that a body in uniform motion continues to move in straight
line path with a uniform speed, e.g., when a moving train stops suddenly a
person sitting in it falls forward. This is because as the train stops, the
lower part of the person's body comes to rest along with the bus while upper
part of his body continues to remain in motion due to inertia of motion and
thus he falls forward.
(iii) Third
part says that a body moving with a uniform speed in a straight line cannot
change its direction of motion by itself. For example, when a bus takes a sharp
turn, a person sitting in the bus gets force acting away from the centre of the
curved path due to his tendency to move in the original direction.
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