Pressure

Pressure

Thursday 4th February 2021

Pressure

• We looked at pressure in gases a few weeks ago.

• Pressure is caused when gas particles collide with each other and the container that they are in.

• By doing so they exert a force, which in turn applies pressure.

Multiple Choice

Which of these factors can increase the pressure of a gas?

• Increasing the temperature.

• Increasing the volume of the container.

• Decreasing the number of gas particles in the container.

Pressure equation

• Pressure is described as force applied per unit area.

• Pressure is measured in Pascals (Pa).

• Area is measured in m2.

• Force is measured in Newtons (N).

• If a force of 100 N is applied to an area of 10m2, the pressure would be equal to = 100 / 10.

• Pressure = 10 Pa.

Multiple Choice

A force of 225 N is applied to an area of 75 m2. What is the pressure?

• 3 Pa

• 16'875 Pa

• 5 Pa

• 0.33 Pa

Open Ended

Why might it hurt more if someone were to stand on your foot in high heels compared to someone standing on your foot in snow boots? Use the terms pressure and surface area in your answer.

Boyle's Law - Pressure in Gases

• Boyle's law states that if temperature and number of particles remain constant then pressure and volume are inversely proportional.

• PV = C

• This means that pressure will increase as volume decreases.

Boyle's Law

A sealed syringe contains 10 m3 of air at a pressure of 1 Pa. If the plunger is pushed so that the volume decreases to 4 m3, what will the new pressure be?

P1 = 1 Pa; V1 = 10 m3; V2 = 4 m3; P2 = ?

P2 = P1V1 / V2

P2 = 10 x 1 / 4

P2 = 2.5 Pa

Multiple Choice

In a sealed system of a volume of 75 m3, there is a pressure of 25 Pa. To increase the pressure to 100 Pa, what should the new volume be?

• 18.75 m3

• 300 m3

• 33.33 m3

• 55 m3

Open Ended

Boyle's law requires the temperature of a system to remain constant. Why does pressure increase as temperature is increased?

Pressure in Liquids

Pressure in a liquid varies with depth.

We can find the pressure of a liquid within a column using the following equation.

Open Ended

Why did the dummy deflate when the pressure was increased in the chamber? (remember this was to simulate going deep underwater).

Pressure in Liquid

The density of water is 1,000 kg/m³. Calculate the pressure exerted by the water on the bottom of a 2.0 m deep swimming pool. (Gravitational field strength = 9.8 N/kg).

h = 2.0 m; p = 1000 kg/m³; g = 9.8 N/kg.

P = 2.0 x 1000 x 9.8

P = 19'600 Pa.

Open Ended

What is density?

Multiple Choice

A stone is dropped into a lake. Calculate the increase in pressure on the stone caused by the water when it sinks from 1 m deep to 6 m deep. (The density of water is 1,000 kg/m³ and gravitational field strength is 9.8 N/kg).

• 49'000 Pa

• 58'800 Pa

• 68'600 Pa