Circular motion plays an important role in nature and technology. So, the planets move on (approximately) circular orbits around the sun. Other examples are the rotating armature of an electric motor or the crankshaft of a gasoline engine.
This Java applet simulates such a circular motion and demonstrates how position, velocity, acceleration and acting force vary in time. The "Reset" button brings the rotating body in its initial position. You can start or stop and continue the simulation with the other button. If you choose the option "Slow motion", the movement will be ten times slower. You can adjust radius, period and mass by using the corresponding input fields. The radio buttons give the possibility to select one of four physical sizes.
The radius vector (red) joins the center of rotation (the origin of the coordinate system) to the revolving body. The velocity vector (violet) is tangential to the circle and perpendicular to the radius vector. The vector of acceleration (blue), surprisingly, is directed inside (towards the center). Here acceleration doesn't mean an increase or decrease of speed (magnitude of velocity), but a varying direction of motion. The same is true for the force (green) on the moving body. The terms centripetal acceleration and centripetal force express that these vectors are directed towards the center of the circular motion.
© Walter Fendt, March 25, 2007
Last modification: March 21, 2008