This project is good for showing how commonly gravity is applied in everyday tools and equipment. Obtain a pair of saucers, two glasses, a needle and a long candle. Have students slice off the bottom end of the candle so the wick is exposed on both sides. The needle needs to be pushed into the center of the candle and each end of it balanced on the rims of both glasses. The saucers are placed under the wicks and then both ends of the candle are lit. This is a great chance to watch how gravity affects objects. Each time the heavy side of the candle is pulled down, the wax melts and drips down more rapidly, making that side lighter and allowing it to rise again.
When children see this smaller scale version of a larger event, they have the chance to better understand the original occurrence by relating it to their project results. Students should drop some marbles into a baking tray filled with an inch or so of evenly-spread flour. Each time they drop a marble and carefully take it back out of the tray, they are watching the formation of craters. The spread of debris from the force of the impact is simulated by the dispersed flour. Once the project is completed, explain to them how meteorites cause similar reactions when they strike the Earth. Show them pictures of craters on the moon, or let them observe them through a telescope.
This experiment gives children the chance to see a visual reference point for center of gravity. Have them put a hole near one end of a square of cardboard and help them nail it to a wall. A small iron weight, or a fishing sinker should then be attached to a piece of string and hung on the nail. Draw a line along the string's path and then repeat the process by using another hole near a different edge of the cardboard. Once the two lines intersect, the students have located the central point of gravity and are better equipped to grasp the concept the next time it is explained to them.
Galileo put to rest the idea that heavier objects fall faster than light ones by dropping iron balls of identical shape but different mass from close to 200 feet in the air. The same experiment is easily recreated from far more reasonable heights with two balls of different mass but identical shape. A small step ladder will help a child get far enough off the ground to record what happens over the course of 10 or so trials when each ball is dropped simultaneously. Bringing in items of differing mass but the same shape and items dissimilar in size, mass or shape help drive home the concept of wind resistance as a major influence on gravity's pull.