A balloon filled with helium. You can get them at party supply stores, novelty shops, fetes, shows and some toy stores, or try the Yellow Pages.
A car
A driver of the car
What to do
Sit in a car with a helium-filled balloon suspended by a string. Make sure the balloon is free to move but does not block the driver's vision.
Buckle up and ask the driver to drive somewhere - school, shops, sport - wherever you like.
As the car accelerates you will be pushed back into you seat.
What happens to the balloon?
What's happening?
When the car accelerates, you are pushed back into your seat but you will see that the balloon moves forward. When the driver hits the brakes quickly your body lurches forward and the balloon flies towards the back of the car.
The balloon is affected by the principles of buoyancy. Objects float because of buoyancy. In physics, buoyancy is an upward force which allows an object, like a boat, to float or at least to appear to become lighter. If the buoyancy of an object exceeds its weight, then the object floats; if the weight of an object exceeds its buoyancy, the object sinks. It was the ancient Greek, Archimedes of Syracuse, who first discovered the law of buoyancy, sometimes called Archimedes' principle.
A helium-filled balloon floats because the surrounding, heavier air is being pulled down with a greater force and the lighter balloon is in its way. The balloon is, in effect, being pushed upward by the heavier air. The helium balloon is buoyant in air the same way a boat is buoyant in water.
The helium-balloon moves forward in the car based on the same principle of buoyancy. In the car, you're not the only thing that gets pushed back while accelerating. CDs, toys, anything that is loose in the car will be dislodged. Even the air feels the force and moves toward the back of the car. The heavier air is pushed past the balloon and with the heavier air crowding the back of the car, there's no place for the balloon to go but forward. The heavier balloon pushes the balloon forward.
Applications
Helium is a colourless, odourless, tasteless gas and the second lightest of all the gases. The lightest gas is hydrogen. It is the second most common element in the universe. Our supply of helium comes from natural gas deposits and is a limited resource. The typical helium atom consists of a nucleus of two protons and two neutrons surrounded by two electrons.
Helium was first discovered in our Sun. About 25 percent of our Sun is helium. Helium is the by-product of nuclear fusion involving hydrogen. It is used in cryogenics, in deep-sea breathing systems, for inflating balloons, and as a protective gas for many purposes.
