Safety: Make sure you have adult supervision as you will be lighting both ends of the candle.
This experiment teaches how combustion and Newton’s Third Law of Motion. A candle, balanced between a pair of glasses, rocks or up and down on its own.
Carve the bottom part of the candle so the wick is showing. Make sure that the bottom end had more wax than the top. Then make a hole in the candle half way in the middle. The hole has to be big enough for a nail (or pin) to fit in. Place the nail in between 2 glasses. Then have a adult light both ends of the candle. One person hold the candle in the middle and the other lights both ends.
The motion continues as long as the candle continues to burn. If one side of the candle starts out heavier than the other, the motion of the candle will act to equalize the mass on either side of the pivot point
The candle moves in response to forces acting on it, trying to reach equilibrium.
The combustion reaction turns the candle wax into carbon dioxide gas and water vapor, making the burning end of a candle lighter.
If one side of the candle burns more quickly than the other, the lighter side of the candle moves up. The lower side of the candle is angled such that the flame melts the wax, causing it to drip down.
This not only lessens the mass at that end of the candle, but the force from the dripping wax actually pushes the end of the candle up! This is Newton’s Third Law of Motion, which states that for every action, there is an equal and opposite reaction.