Downhill Racing (Derby physics)

Flash Animation by Mark Cowan
ePhysics, UCLA

Which is faster, a thin disc or a hoop? A snowball accumulating more and more snow or an unraveling garden hose? Use the animation below to find out. How does the mass or radius of an object affect the time that it takes an object to reach the bottom of the slope? Use this animation to answer these and other questions by doing the following-

  1. Choose an object for each of the two hills. Click on one of the 6 radio buttons on the left side of the animation in order to select which object you wish to have slide down the left hand slope and click on one of the 6 radio buttons on the right side of the animation in order to select which object you wish to have slide down the right hand slope.
  2. Click on the buttons marked properties in order to set the characteristics of the two objects.
  3. Drag the objects in order to set the initial locations of the objects.
  4. Press play.

Keep in mind the following when using this animation:

  • The elevation of an object is measured from the center of the object.
  • The clocks measure time in virtual seconds and not actual seconds.
  • Each object's clock will stop when the object's elevation is equal to zero (the bottom of the hill). In general, the clock will over estimate the time that it takes for a given object to reach the bottom of the hill by 0.1 virtual seconds.
  • The animation ignores dissipative forces.