The Physics of Circular Motion The Physics of Circular MotionA particle moving in a circle with constant speed has uniform circular motion. The particle's velocity vector changes continuously in but its magnitude remains constant.
Graphic of particle moving in a circle
The acceleration of a particle P is expressed with the classical equation,
Equation for circular acceleration, a equals velocity squared divided by r.
and the acceleration always points inward toward the center of the circle. Here, the magnitude of both velocity and acceleration remain constant but their directions are changing continuously. This center seeking acceleration is called "centripetal" acceleration.
If the angular velocity of a spinning object is increasing or decreasing then a point P on the object will experience both a radial acceleration and a tangential acceleration. The combined acceleration is equal to:
Acceleration is equal to the square root of Ar squared plus At squared.
Graphic of spinning disk with point P, angular velocity is decreasing.
If a spinning disk is moving,
Graphic of moving spinning rigid disk
then a point P on the disk will experience a centripetal acceleration and a varying tangential velocity.
Graphic of velocities and a graphic of acceleration.
The Ball-of-Light Particle Model basically predicts the centripetal acceleration and gravitational acceleration are equivalent. When a galaxy is spinning and moving with translation,
Graphic of spinning, moving spiral galaxy
then the galaxy will undergo greater induced levels of gravity on the side of the galaxy where its velocity is maximum.
Graphic of velocities and gravitational levels within a spiral galaxy
Since the galaxy is not a rigid object, this higher gravitational force will distort the galaxy.
Graphic of a spiral galaxy that is circular and distorted.