Pressure

  • Pressure relates to the intensity of a force acting on a specific area. It’s calculated by dividing the force by the area over which it’s spread. Measured in units called Pascals (Pa), it’s a derived quantity in physics.

  • An increase in pressure in a gas or liquid can often result in a decrease in its volume if the temperature is kept constant. This is captured in Boyle’s Law, which states that: P1V1=P2V2, where P is pressure and V is volume.

  • Pressure in a gas arises from the force exerted by gas particles colliding with the walls of the container. Greater pressure will result from more frequent and/or more forceful collisions.

  • An increase in temperature increases the pressure of a gas if the volume is kept constant. This is because the kinetic energy of gas particles is directly proportional to the temperature, thus raising the temperature causes particles to move faster and collide more often/forcefully with the walls of the container.

  • Similarly, an increase in the volume of the container, while keeping temperature constant, will decrease the pressure of a gas. This is because increasing the volume results in fewer collisions with the container walls per unit of time, reducing the pressure.

  • Atmospheric pressure is the pressure exerted by the weight of the atmosphere on the earth’s surface. It decreases with altitude due to the decreasing density of the air.

  • Crushing cans are a practical demonstration of atmospheric pressure. When air is removed from a can, the external pressure becomes greater than the internal pressure, causing the can to be crushed.

  • Another key point to remember about atmospheric pressure is that it can support columns of liquids. For example, atmospheric pressure can support approximately 10m high water column.

  • Manometers and barometers are commonly used devices to measure pressure. In particular, a barometer measures atmospheric pressure.

  • Lastly, remember that pressure and volume are inversely proportional in closed gas systems at a constant temperature, while pressure and temperature are directly proportional in a closed gas system at a constant volume.