Download Bowling Ball Pendulum

Bowling Ball Pendulum:
Key Concept: Conservation of Energy
Energy cannot be created or destroyed. It can only
change form. There are two observable forms of
energy, kinetic energy (or “energy in motion”) and
potential energy (or “stored energy”). The total
energy of a system is equal to the sum of its potential
energy and its kinetic energy: TE=KE+PE
How It Works:
In the picture shown to the left, the ball is at rest.
Since it is at rest, it has zero kinetic energy. The ball
does, however, have potential energy due to the force of
gravity. Its potential energy is given by:
PE = mgh
where m=mass of the ball, g=gravity, and h=height of the
ball.
So, as the height increases, the potential energy
increases.
The kinetic energy is given by:
KE=1/2 mv2
where m=mass of the ball and v=velocity of the ball.
So, as the velocity increases, the kinetic energy
increases.
Now, if the ball is pulled to position A shown in the
picture to the left, its potential energy increases since
its height increases. However, since the ball is at rest, it
still has zero kinetic energy. The total energy of the
system has increased, though, since the potential energy
has increased.
If the ball is released, it begins to move, so its kinetic
energy increases. Since the total energy is conserved, as
the kinetic energy increases, the potential energy
decreases (and vice versa). At position B in the picture,
the potential energy is at its minimum and the kinetic
energy is at its maximum. At position A and C (the
turning points), the potential energy of the system is
maximum, and the kinetic energy of the system is zero.
If forces on this system other than gravity and the
tension of the string were neglected, the ball would
continue to oscillate forever.
When the ball moves from point A to point C and back to
point A, we say that it has completed one revolution. The
time it takes to complete a revolution is called the period.
The period is given by:
T= l/g
where l=length of the string and g=gravity.
Question: What will happen to the period if the mass of
the ball is increased? Will the period increase, decrease,
or stay the same?
Question: What will happen to the period if the string is
lengthened?
Question: Why doesn’t the ball swing to a height higher
than its starting height?