When a basketball is bounced on a wooden floor all we see is a ball moving
up and down physicists on the other hand see a stream of equations that attempt
to make logical and empirical sense of the whole floor-and-ball situation.
One such physicist was Sir Isaac Newton. In fact, when he looked at a bouncing
ball, it led him to propose a law we still use today to determine how bouncy
a particular object is: the law of restitution
When one object comes in physical contact with another object a lot of
stuff happens: certain forces come into play, velocities of the objects are
affected and energy is converted from one form to another. Let's consider the
most basic example bouncing a basketball on a rigid floor. When you drop the basketball from a given height
you probably just see the ball dropping to
the floor and bouncing up back towards your hands. On the surface, this looks
simple enough, but there are a number of physical phenomena at play. When the ball
is held at a certain height above the ground, it has potential energy but as
it's dropped that potential energy is converted into kinetic energy just
before the ball touches the floor it still has kinetic energy but the
moment the ball touches the floor a fraction of its kinetic energy is lost
in the form of sound or heat this is why the ball makes a sound and also gets
heated ever so slightly when it's bounced on a hard surface this is also
why the ball loses some of its height with every subsequent bounce you may
have noticed that a basketball bounces very well but a plastic ball isn't as
good and if you're to bounce a lead ball it would hardly bounce at all rubber is
more elastic than plastic which is in turn more bouncy than lead every object
has a different way of reacting while interacting with another object given
that how do we compare any two objects in terms of their bounciness for this we
use a term called the coefficient of restitution
the coefficient of restitution of a material tells you how it interacts with
other objects it indicates the elasticity of the collision of a given
object with another it's a dimensionless quantity whose value lies between zero
and one if an object has a high coefficient of restitution it is
considered quite bouncy and if it has a low coefficient of restitution it won't
be as bouncy the coefficient of restitution is an integral part of
newton's law of restitution which states that wind two objects collide their
speeds after the collision depend on the material from which they are made
mathematically the coefficient of restitution can be expressed as the
ratio of relative speed between the two objects after the collision and the
relative speed between the two objects before the collision
a collision where no kinetic energy is lost is called a perfectly elastic
collision and for such a collision to occur the value of the coefficient of
restitution would be equal to one such a collision would be the bounciest
reaction an object could possibly give however a perfectly elastic collision is
impossible in the real world as some energy is always lost during the
collision and released in the form of heat or summoned on the other side of
the spectrum is a perfectly inelastic collision wherein the two objects stick
together and move together after the collision in this case the coefficient
of restitution would be zero most real-life collisions are somewhere
between these two extremes sports equipment companies pay a lot of
attention to the coefficient of restitution of their products that are
supposed to bounce or be physically deformed in some way or another
in fact sporting authorities in some countries even specify an acceptable
value range for the coefficient of restitution of balls and other sporting
equipment all-in-all the coefficient of
restitution is an indicator of the general bounciness or elasticity of an
object therefore next time you find yourself conflicted about choosing
between two brands of tennis balls at a sports shop check their coefficient of
restitution values and you will be able to make a better bouncier decision