There are numerous experiments that children can conduct with their own toy cars. Preschoolers will enjoy building a steep ramp and a less steep ramp with blocks or pieces of wood, and then guessing which ramps their cars will drive down faster. Older children can use ramps with different materials covering the surface, such as sandpaper or carpet, and time their races with stopwatches. They can also predict how far a car will continue to drive after reaching the bottom of each ramp.
Children who are old enough to fold their own paper airplanes can conduct a simple experiment to determine what kind of paper makes the best paper airplane. Using the same paper airplane pattern, fold airplanes out of different weights and types of paper, such as copy paper, wrapping paper, wax paper, card stock and newsprint. Fly each airplane from the same starting position and measure the distance each airplane travels. Have each child take turns flying the airplanes to accumulate a set of data, and average the distance for each type of paper airplane.
Kids can quickly learn how energy propels a vehicle through a simple experiment using a straw, tape, balloons and fishing wire. Blow up and tape a drinking straw to a balloon, and then let the air out of the balloon. Thread the fishing wire through the straw and then tie each end of the fishing line to two chairs or other sturdy objects. Bring the balloon to one end and blow the balloon up again. Let go of the balloon and measure how far the balloon travels along the fishing wire. Experiment with blowing the balloon up using more and less air to see how much air is needed to propel the balloon.
Older elementary school children will enjoy experimenting with building their own boats. Give students ample time to design and construct their own boats with sails, propellers or homemade jets powered by baking soda and vinegar or antacids. Set out a large wading pool or use a community or school pool for the race. Measure how far each boat gets across the pool and the time it takes for each to travel. For an additional challenge, race again after weighing each boat down with marbles or washers.