Weird Science: Spinning Marble

HONOLULU (HawaiiNewsNow)- The one and only Dr.V from Oceanit Hawaii is back! He shows Taizo how to use a glass cup to spin a marble! Check out the video!

Dr. V Show:  Spinning Marbles

Things you will need:

  • Glass with a mouth narrower at the top than the bottom
  • Small ball

The Experiment:

Please to do this and all other experiments under the supervision of an adult. Place the marble or ball on a table top and trap it under the glass. Start wiggling the glass so that you get the marble to start rolling around the rim of the glass. As you get it spinning faster, what happens to the marble? Once you've got your marble spinning pretty well in the glass, lift the glass off the table. What happens to the marble?

How does it work?

Why does the marble stay in the glass and not fall out? Centripetal force is the force keeping the marble stuck to the glass as it's spinning around. This force is a result of the marble's path and the shape of the glass. This is the same force you feel applied to your body while you're riding in a car and going around a curve, and the faster you go, the greater the force. The reason you feel this force is because of Newton's first law, an object in motion tends to stay in motion unless an external force is applied to it. In this case, once the marble is moving, it wants to move in a straight line, but because the walls of the glass are curved, the marble follows the curve of the glass. This is the same force that keeps pressed to your seat as you do a loop on a roller coaster!