Car Tire Air Experiment

Science Fair Project Idea - How compressed air is used in automobile tires

Science Fair Project Idea - How compressed air is used in automobile tires

We all know that bicycle tires and most automobile tires are filled with air. At first thought it seems strange that a substance like air can hold up the great weight of a heavy automobile. Naturally we ask how this air is different from the air around us.

What happens if a nail punctures the tire? Sometimes when the outer covering of the tire becomes badly worn a " blow-out " occurs with a noise like an explosion, tearing a hole in the tire. What does this indicate to you concerning the condition of the air within the tire?

It is evident that the compressed air in the tire is able to hold up the weight of the automobile amounting to several thousand pounds, just as the compressed air in the diving bell resists the pressure of the water.

If you have ever ridden in a solid-tired automobile and then in one having pneumatic or air-filled tires, you have noticed that in the latter case the jars caused by the roughness of the road were not felt as much. This observation shows that the compressed air in the tire acts like a spring. The following simple experiment will show this effect of compressed air.

Science Fair Experiment - Air Pressure Project

Bounce together on the floor a new, perfect tennis ball and a tennis ball in which a small hole has been made by a pin or nail. Measure the height of the bounces.

Result? In the same way compare the bouncing of a basket ball which is just sufficiently filled with air to cause it to keep its shape with the bouncing of a similar ball into which a large amount of air has been pumped.

From the observations you have made you will conclude that the compressed air in the automobile tire is able to support a great weight and gives springiness (elasticity) to the tire. Many tire-filling compounds have been tried but none has been successful because nothing has been found that will give the springiness possessed by compressed air. It is evident that in the construction of an automobile tire, first, the tire must be air-tight to prevent the escape of the air and, second, it must be of sufficient strength to resist the pressure of the imprisoned air. An examination of an automobile tire will show how these two requirements are met. The inner tube made of elastic rubber is air-tight. The air is pumped in through a metal tube in which is a valve that will allow air to be pushed in but prevents its escape.

The outer tire or shoe is not necessarily air-tight but provides the strength to resist the outward pressure of the confined air. It is very strongly made of a combination of cotton fabric or cord and rubber. In bicycle tires where the weight supported is not so great, frequently only one tube is used. What two properties must this tube possess? Air is forced into the tire by an air pump.

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