pressure and volume have an inverse realtion
as you decrease the volume, the pressure will increase.. and with the increase in volume pressure will decrease.
for more, search out Boyle's Law at Google and Wikipedia
Boyle studied the relationship between the pressure p and the volume V of a confined gas held at a constant temperature. Boyle observed that the product of the pressure and volume are observed to be nearly constant. The product of pressure and volume is exactly a constant for an ideal gas.
p * V = constant
Boyle's law explains an inverse relationship between the volume and pressure of a gas. For example, if the volume of a gas doubled, the pressure it exerted ...