Marbles are a useful component in physics experiments. They are inexpensive and readily available. They are close enough to identical in weight, size and shape to meet the purpose of most physics classes. Their physical properties are useful for demonstrating the principles of energy transfer, motion, momentum, weight and volume.
Volume and Density
Marbles are useful for experiments on volume, weight and density. Since they are non-porous and heavier than water, they will always displace water equal to their own volume and can be used in basic demonstrations of displacement. A simple experiment using displacement is to have students calculate the densities of marbles of various types, sizes and materials. Filling a beaker with marbles then measuring how much water still fits in the beaker can help students visualise how porous materials hold water.
Marbles can also be used in experiments demonstrating the principle behind fluid pressure. Air pressure, for example, is not actually a single steady pressure but rather the combination of the force of many small collisions between air molecules and surrounding surfaces. Students can turn the tray of a spring scale upside-down and pour a steady stream of marbles onto the scale, letting them roll off into a surrounding barrier or container. The reading on the scale should be relatively steady even though there is no single weight on it.
Gravity and Momentum
Marbles also roll with very little friction which makes them useful in experiments designed to study motion and momentum. You can make tracks for marbles out of foam pipe insulation. Use insulation with a 1-1/2 inch diameter and cut it in half along its length to create two U-shaped tracks. These can be connected using tape and bent or curled into loops, ramps and curving tracks. Set up a ramp at the beginning of the track and measure how much initial height is required for a marble to successfully travel a loop or how initial slope affects speed on a long, straight piece of track.
You can create a simple pendulum out of a marble by attaching thread or string to one point on the marble's surface with a small drop of strong glue. After the glue dries, you can suspend the pendulum from a clamp and use it to explore the relationships between a pendulum's weight, length and period. If you attach a second string to a point on the marble near the first, you can constrain the pendulum to swing in one direction. Set up two or more constrained pendulums in a row and let them collide to examine the transfer of momentum.
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