# Physics: Circular Motion

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The Circular Motion physics calculator provides equations related to the basic mechanics of circular motion. Circular motion, rotational velocity and acceleration, and angular frequency has applicability to many fundamental physical phenomena.  The formulas include:

• Centripetal Acceleration as a function of tangential velocity and radius,CLICK HERE.
• Angular Frequency as a function of orbital period,CLICK HERE.
• Speed of Circular Motion as a function of orbital period and radius,CLICK HERE.
• Radial Acceleration as a function of orbital period and radius,CLICK HERE.
• Acceleration in non-uniform Circular Motion,CLICK HERE.

# Uniform Circular Motion

Uniform circular motion is defined by a particle or point moving at a constant speed around a circular path.

It is useful to decompose the components of velocity and acceleration into a component tangent to the circular path and perpendicular to the circular path.  There is no tangential acceleration if the speed of the circular motion is constant.  There is, however, a radial acceleration, a_"rad",inward and therefore perpendicular to the circular path.  This radial component of acceleration changes the direction of the velocity vector, vecv, but not the speed of the point or particle. It an be shown from the ration of the similar sides of the triangles represented in Figure 1 that:

|Deltavecv| / v_1 = (Deltas)/R.  And from this directly:  |Deltavecv| = v_1 /R * Deltas

|Deltavecv| /(Deltat) = v_1 /R * (Deltas)/(Deltat) = a_"avg"

As the points get closer together and Deltas gets smaller and smaller, we get the magnitude of the instantaneous acceleration:
a = lim_(t->0) [v_1/R (Deltas)/(Deltat)] = v_1/R * lim_(t->0) (Deltas)/(Deltat) = v_1/R * v_1

a_"rad" = v^2/R  1  [ See the calculator button labeled Centripetal Acceleration ]

Since the circumference of circular path is circumference = 2*pi*R, we can divide this distance by the time it takes to travel around the circumference.  The time it takes to travel once around the circumference is the rotational period, T.  So, the speed of the point moving in a circular motion is:

v = (2*pi*R) /T  2 [ See the calculator button labeled Speed of Circular Motion ]

and since the rotational frequency is related to the velocity and the radius as follows:

omega = v/R = (2*pi*R) /(T *R) = (2*pi) /T [ See the calculator button labeled Angular Frequency from Period ]

Substituting the expression for v into the equation for acceleration, a_"rad" = v^2/R, we get:

a_"rad" = ((2*pi*R) /T)^2/R = (4 * pi^2*R)/T^2  3 [ See the calculator button labeled Radial Acceleration (R,T) ]

# Non-uniform Circular Motion

For non-uniform circular motion, the tangential acceleration is not zero, as it was for uniform circular motion, so:

a_"tan" = (d|vecv|) /dt   4

So, the acceleration vector for non-uniform circular motion is:

veca = |(dvecv)/ dt| = sqrt(a_"rad"^2 + a_"tan"^2)  [ See calculator button labeled Acceleration - Non-uniform Circular Motion ]

# References

1. ^ Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 88, eq 3.28
2. ^ Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 89, eq 3.29
3. ^ Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 89, eq 3.30
4. ^ Young, Hugh and Freeman, Roger.  University Physics With Modern Physics.  Addison-Wesley, 2008. 12th Edition, (ISBN-13: 978-0321500625 ISBN-10: 0321500628 ) Pg 90, eq 3.31