PURPOSE: To see convection currents.

DESCRIPTION: Take a iron ball as in the picture above and cool it in liquid nitrogen for 5 minutes. Hold it in front of a slide projector and watch the convection currents move downward. Now take the heat gun and turn it on for 3 or 4 minutes and hold it sideways in front of the slide projector. You will see the convection currents flow upward. If held the right way you can do both at once. This phenomenon is often seen when the sun shines brightly onto surfaces like cars and roads, and is responsible for the twinkling of stars.

SUGGESTIONS: Practice is required. The cold currents show up much better on the screen. Use proper safety precautions.

EQUIPMENT: Heat gun, iron ball, liquid nitrogen, slide projector and screen.

SETUP TIME: 50 min..