Unit 4 Vocabulary Terms
Circular Motion
Radius - R
The radius is defined as half the diameter of a
circle or the distance from the edge of a
circle to its center. The radius is a unit of
distance and can be measured in any unit of
length. The symbol for the radius is “R”
Period - T
The period is defined as the amount of time
required for one object to complete one
revolution around another object. The
common unit for the period is the second.
The symbol for the period is “T”.
e.g. The period for the earth to revolve around
the sun is 365 days.
e.g. A tether ball may complete one revolution
around a pole in 3 seconds.
Frequency - f
The frequency is the number of revolutions or
cycles occurring in one second of time. The
symbol for frequency is “f ”. The common unit
of frequency is cycles/sec also known as a
Hertz (Hz).
e.g. The tether ball can complete 1/3 of a
revolution or cycle in one second. f= 0.333
Hz
Relation of Frequency to the Period
The frequency is related to the period by the
following expression:
Period = 1 / Frequency
T = __1__
f
Circular Velocity - Vc
Remember that the velocity is equal to the
change in displacement over the change in
time. For a circle, we just replace
displacement with circumference and time
with the period.
vc = 2πR circumference
T
period
Centripetal Acceleration - ac
The acceleration an object experience as it travels in a circle is
called the centripetal acceleration. Although the object is
traveling at a constant speed, its direction is continuously
changing thus its velocity is also constantly changing. As a
result, the object experiences an acceleration towards the
center of the circle (centripetal).
ac = v2
R
Centripetal Force - Fc
Centripetal force is the force resulting from a
mass experiencing centripetal acceleration
towards the center of a circle.
Fc = mac
Fc = m v2
R
There is NO Centrifugal Force!
When released, an object will not fly
backwards from the center of the circle.
Instead, the object will fly away tangentially
from the edge of the circle. Centrifugal
means “center fleeing”. This is common
misconception in circular motion.