Explain Why A Tire Or Balloon Expands When Air Is Added

A  tyre or balloon expansion when air is added can be explained by the kinetic theory of gas, “ gas particles do not have their fixed volume or definite shape,  they assume the shape of their container  gas particles or molecules collides with themselves or with the wall of their container. Air is a gas , the air molecules added into the balloons or the tyre assumed the shape of the container ( tyre or balloon)  and collision between the molecules and the wall s of the container exert pressure on it and then it expand.