This experiment is easily done with a glass of water and a handful of pennies. Children will aim to show the properties of a liquid that allow their surfaces to resist an external force. Pennies are dropped one at a time into a nearly full glass of water. As the pennies displace the water, it will rise, and a bubble will push upwards from the lip of the glass. After a while, the pennies must be carefully inserted, and the surface tension of the water will be quite apparent as it resists them.
Bernoulli's principle of fluid dynamics demonstrates that moving air will decrease in pressure as it increases in speed. This is the reason airplanes and birds can fly. Demonstrating Bernoulli's principle is easy; use a hair dryer to blow a small beach ball up into the air. The beach ball will appear to levitate as it is kept aloft by low-pressure air moving in from the sides to keep it in the hair dryer's stream.
Children can easily create dramatic demonstrations of the power of the sun. A sunny day and a magnifying glass is all a child needs to burn wood or grass; have him spell his name on a board. A hot dog or a tomato in a cardboard box covered with tinfoil can be cooked in a matter of minutes on a sunny day.
There are many ways a child can nurture an interest in nature and the environment while creating a fun, fast, and appealing science project with this theme. The child can create or buy an ant farm with some adult supervision. An aquarium with fish in it, or a terrarium with frogs and insects are possibilities. The project can be as simple as creating a maze for a hamster or other small pet.