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Linear motion is when an object moves
forward in a straight line. But there are times when the
motion has constraints, such that it moves back and
forth in regular motion. This is called periodic motion
and can be seen in such examples of a weight on a string
and seen how it swinging back and forth or a ball will
bouncing up and down. If you have noticed
that type of motion, you may have some questions:
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What are some examples of periodic
motion?
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What are some common characteristics
of this motion?
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How is periodic motion useful to me?
This lesson will answer and explain
those questions.
Examples of periodic motion
Periodic motion is any motion that repeats itself.
Examples of periodic motion include a bouncing ball,
vibrating spring, circular motion, and a pendulum. If you drop a ball, it will
start to bounce in a regular fashion. A good rubber ball
or a super-ball will keep bouncing for a long time.
Because of internal friction and air resistance, the
ball bounces less and less each time, until it finally
stops. A perfect ball�without friction�would bounce
forever.
If you start a spring vibrating, it will continue to
move back-and-forth for a long time. Internal friction
slows it down or dampens its vibrations. Spin a weight on a string
around in circles. This is a periodic motion that
repeats itself every rotation. The Earth rotates around
the Sun in a periodic circular motion. If you swing a weight on a
string, it will go back and forth in regular periodic
motion. Once it got started, such a pendulum would move
back-and-forth forever if it was not for internal
friction in the string and air resistance. You strike a tuning fork, and
you can see the ends vibrate back and forth. The
vibrations cause the air to vibrate, resulting in sound
or a musical note. Characteristics
of periodic motion All objects that are
in periodic motion have three similar characteristics:
velocity, period, and amplitude. They all have a velocity. You
can measure the velocity of a bouncing ball, the weight
on a pendulum, or such.
The period is the time the object takes to go back and
forth. If you spin a weight on a string, you can measure
the time it takes to go 1 revolution. Drop a ball and
measure the time it takes until it bounces back up. That
is its period. Sometimes frequency is
used instead of period. Frequency is the reciprocal of
period. That means that frequency equals 1 divided by
the time of the period.
f = 1/t The amplitude is 1/2 the
distance the object goes before from one side of the
period to the other. For an object in rotation, the
amplitude is the radius of the circle (1/2 the
diameter). There are many devices that use
the characteristics of periodic motion. A clock is the
most common device. We can also use the fact that the
motion repeats itself regularly to predict what will
happen, like in setting up a calendar from the Earth's
periodic motion. Another use for the
knowledge of periodic motion is that it applies to the
study of wave motion, including light, sound, and music. A bouncing ball and
vibrating spring are examples of periodic motion.
Velocity, period, and amplitude are common
characteristics of periodic motion. There are various
applications of these characteristics. |
