Laws of Motion
Newton's Laws of Motion
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Why does an
object move? What are the laws that make it move the
way it does?
Sir Isaac Newton (1642 - 1721) answered these
questions.
First law
of motion: A body continues in a state of
rest or uniform motion in a straight line unless, it
is acted upon by external forces.
Push a ball
along the floor. It moves but comes to rest after
some time, even when there is no apparent external
force acting on it. But then there is an external
force. This force is friction. If we remove
friction the ball will not stop, unless another force
were to make it stop.
What is force? First law of motion
helps us answer this question.
Force
is the push or pull, which changes the state of rest
, of a body, or that of uniform motion in a straight
line.
Force has both
magnitude and direction so it is a vector quantity.
What is
inertia?
First law of motion helps us to answer this question
also.
Inertia:
A body, on its own, is unable to change its state of
rest or of uniform motion in a straight line. This
property is its inertia.
Take a tumbler.
Place a cardboard piece on it. Now put a coin on this
cardboard piece. Pull out the cardboard with jerk.
What happens? If you do it correctly, the coin will
drop into the tumbler. Why? The answer is inertia
of rest. The force was applied on the cardboard
and the coin got left behind because of its inertia
of rest. Can you think of some other examples. Reason
out what happens to passengers standing in a bus when
it moves suddenly. Another example: what happens when
we shake off the dust from a cloth or a blanket?
Imagine that
the bus, in the above example comes to a sudden halt.
The passengers are thrown forward, unless they hang
onto something. This is inertia of motion. The
same bus ( a useful analogy ! ) gets moving again and
goes around a corner at a fast speed. The passengers
are thrown outwards. This is inertia of direction.
Can you think of more examples? If you can and want
them checked send them to me by e-mail or if you want
me to send more examples let me know.
It takes more
effort to stop a heavy truck than to stop a car, why? This is due to linear
momentum.
Linear
Momentum (p): This is the total quantity of motion in
a moving body and is given by the product of its mass
(m) and its velocity (v).
p = m v
Mass is scalar
and velocity is a vector so linear momentum is a
vector. The direction of linear momentum is the same
as the direction of the velocity of the body.
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