Compress a gas at constant temperature and its pressure rises as fast as its volume falls, so P × V stays constant. Drag the volume slider and watch P2 = P1V1÷V2 climb a live pressure-volume hyperbola.
Trap a fixed amount of gas in a cylinder and push the piston in without changing the temperature. The molecules are forced into a smaller space, strike the walls more often, and the pressure climbs. Drag the Volume slider and the piston compresses while the gauge rises; the relationship is Boyle's law, P1V1 = P2V2, which rearranges to P2 = P1V1/V2.
The panel keeps the product P × V in view, and its point is that this number never moves as you slide the volume — that is what makes the pressure-volume plot a hyperbola rather than a straight line. Halve the volume and the pressure doubles exactly; cut it to a quarter and the pressure quadruples. The Initial pressure and Initial volume sliders lift or reshape the whole curve by resetting that constant product.
Watch the gauge readout too: it shows pressure relative to the atmosphere, so below about 101 kPa absolute it reads negative — a partial vacuum, below atmospheric. Put exact numbers on any compression with the Boyle's law calculator, compare it with the volume-temperature law in the Charles's law simulator, or explore the rest of our interactive physics labs.
At constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume, so the product P times V stays constant: P1V1 = P2V2. Halve the volume and the pressure doubles.
The temperature and the amount of gas. The simulator fixes the temperature at 300 K and shows the product PV, which stays the same at every volume — that is the whole content of the law.
Absolute pressure. The simulator works in absolute pressure and also shows the gauge value (P minus atmospheric, about 101 kPa). When the absolute pressure drops below 101 kPa the gauge reading goes negative — below atmospheric.
A syringe or a bicycle pump: pushing the plunger in shrinks the volume and drives the pressure up. Your lungs do the reverse — expanding the chest lowers the pressure so air flows in.