A student seals a sample of gas inside a syringe connected to a digital pressure sensor.
The temperature of the gas remains constant during the experiment.
The plunger of the syringe is pushed in to decrease the volume of the gas, and the pressure is recorded.
The results are plotted on the graph in the figure below.

Explain, in terms of the motion and collisions of gas particles, why the gas exerts a pressure on the inside of the syringe, and why the pressure increases as the volume is decreased.