To make a gravity device.
This is a gravity machine that can be constructed from a candle, a needle, two glasses, and two saucers. Gravity plays an essential role in thousands of mechanical devices. Cut away the bottom of a long candle to expose the wick and push the needle through the middle of the candle. Rest the ends of the needle on the rims of two glasses. Then place a saucer beneath each wick and then light the wicks. As the wax drips from the ends, one side soon becomes lighter than the other. Gravity then pulls down the heavy end, causing it to drip a larger amount of wax on the saucer. This lightens that end of the candle so it goes up while the other end goes down, deposits wax and then goes back upwards again. The candle will then oscillate up and down till the wax is over.