‘An object will remain
at rest or continue to move with constant velocity as long as the net force
equals zero’ (Blazevich, p.44). This first law explains that an object will not
move or can not change its motion unless an external force acts on them.
Inertia is ‘the reluctance of a body to move’ (Bartlett, p.75), so to move any
part of the body, you must first overcome inertia. Moment of inertia is
‘tendency for a rotating body to remain in its present state of motion; equal
to the product of the mass of an object and its radius of gyration’ (Blazevich,
p. 240).Radius of gyration is ‘the distance from the axis of rotation to a
point where the centre of mass of the object could be located without altering
its rotational characteristics’ (Blazevich, p.241). This meaning that the
further away from the pivot point the mass distribution is the larger the
moment of inertia we will get from it and we will have to overcome. See
‘science of levers’ to describe the best lever in a tennis serve taking moment
of inertia into consideration.
Law 2 – Law of acceleration
‘The acceleration of an object is proportional to the net force acting
on it and inversely proportional to the mass of the object: F = ma’ (Blazevich,
p.45). Newton’s second law explains what occurs if an external force does act
on an object. No movement can be initiated without a force. The greater the
mass of the object, the greater amount of force is needed for the same
distance. In tennis the ball is not weighted and therefore when a tennis player
serves the ball will easily accelerate of the weighted tennis racket.
Law 3 – Law of action-reaction
‘For every action, there is an equal and opposite reaction’ (Blazevich,
p.45).This demonstrates that forces never act alone, but in pairs. When the
server exerts the force onto the tennis ball, the tennis racket exerts and
equal and opposite force on the tennis ball. Because the tennis racket is
heavier with more force than the tennis ball, the effect on the tennis ball is
greater than the effect on the tennis racket, therefore giving greater force on
the tennis ball. Ackland et. al. also states that ‘in a serve of tennis, the
player applies a “leg drive” to the court to create an equal and opposite force
that causes the body to leave the ground for impact (added height is a great
advantage in the serve action)’ (p.314).
Thanks for providing this post. I have read it and it's a great approach to Newton's law. But if you could illustrate it with some applications of 2nd law, this would have been better.
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