Defying gravity

by Fellowship Agency September 28, 2017

Pop your safety goggles on, grab a Gratnells tray and defy gravity with this exciting experiment. We used marbles, Skittles & Maltesers but anything small and spherical will do!

Learning outcomes

You will be able to:

  • Create centrifugal force.
  • Experiment to determine which shapes create centrifugal force most easily.

You will need (per demonstration):

  • 1 x Shallow Gratnells (F1) tray
  • 1 x Safety goggles
  • 1 x Clean wine glass (for best results, the glass should be narrower at the stem than at the rim)
  • A selection of small spherical objects, e.g. Maltesers, marbles and Skittles, and something to keep them in (we used a Gratnells mini tray)
  • Video recording equipment (optional)

What to do:

Take a look at our Defying Gravity video.

  • Put the safety goggles on.
  • Turn the wine glass upside down and place it on to the bottom surface of a clean, shallow Gratnells tray.
  • Trap one small sphere under the wine glass.
  • Set up and start your video recording device.
  • Rotate the glass quickly, but do not lift it off the surface of the tray.
  • The object should start to move around the perimeter of the glass and then travel up the side of the glass in a smooth, circular motion.
  • Once the object is moving quickly and has risen up the side of the glass, without stopping the motion, slowly lift the glass up off the bottom of the tray.
  • As long as you keep rotating, the object should stay in the glass!

What is happening?

This activity explores centrifugal (centripetal) force. Centrifugal force is created by the circular energy of the moving glass, which is transferred to the spherical object. The shape and surface of the spherical object and the wine glass are important in establishing centrifugal force. The smoother the better, as this reduces friction, friction would reduce the energy available to generate centrifugal force. A spherical object, in this case a Malteser, would usually move in a straight line if allowed to roll on a sloping surface. However, when the object is trapped inside a wine glass, it is forced to move in a circular motion. The rotating motion in an enclosed space forces the Malteser against the walls of the glass, the walls ‘push back’, or resist, with equal force. The centrifugal force created keeps the object inside the glass, ‘stuck to’ or pushed against the inner surface. Centrifugal force will keep the object in the glass while the circular motion continues. Once the circular motion stops, the downward force of gravity becomes the stronger force and the object falls out of the glass.

Other things to try…

  • As long as your hands, the glass and the tray are clean, and you have permission from a supervising adult, you can eat the sweet at the end of the activity.
  • Which sweet is the easiest to use for this activity? Why?
  • Try using a different shaped glass with the same spherical object. Is it easier or harder to create centrifugal force?
  • Share the photographs and videos of your attempts on social media using #WhatsInMyTray

Health & Safety

As with all Gratnells Learning Rooms What’s In My Tray activities, you should carry out your own risk assessment prior to undertaking any of the activities or demonstrations.

With special thanks to Breckland Scientific who provided the idea for this What’s In My Tray activity and for the music.