Dark and Light Colors

You will need:
 * 100-watt lightbulb
 * Aluminum foil
 * Empty can
 * Black paint
 * Paintbrush
 * Petroleum jelly
 * Cotton swab
 * 2 coins (same variety)
 * Adult supervision

Paint one vertical half of the inside of the can with black paint. Put aluminum foil over top half of lightbulb. When can is completely dry, use cotton swab to put dabs of petroleum jelly on each side of can. Put coins on petroleum jelly and place can on lightbulb covered with foil. Observe which coin falls faster.

The heat from the lightbulb causes the molecules in the petroleum jelly to expand, eventually changing them into a liquid in a process called melting. The temperature at wich a substance melts is called its "melting point." The coin on the side with the dark coating falls more quickly because the dark-colored surface absorbs and retains more heat than the light-colored or shiny surface, even though the heat is distributed evenly inside the can. This causes the petroleum jelly on the dark-colored side of the can to melt faster. Light colors reflect most of the heat-making light waves, which causes that side of the can to remain cooler.

Variations:

Melt a piece of chocolate or wax on the top of the can. The piece of chocolate may show circular waves, much like the ripples a stone makes in the water. This is caused from radiation heat.

Put dabs of petroleum jelly on a straightened paper clip. Hold it over the lightbulb with pliers or a clothespin. The dab closest to the lightbulb will melt first, then each of the others will melt consecutively. This is caused from the heat passing down the wire and is called conduction.

Fill one glass with warm water. Fill another with cold water. Put a drop of food color in each. The one in the warm water will whirl around and up to the top, but the one in the cold water will not. The warm water at the bottom of the glass moves more than the cold water, and rises to the top. The cold water at the top slowly sinks to the bottom. Because there is less motion in the cold water, the food color stays at the bottom of the glass for longer. This is from convection.