P1.3 Pressure Flashcards
Describe the motion of molecules in a gas.
They are in constant random motion
What are the units used for pressure?
Pascal (Pa)
How can the pressure of a gas be increased whilst kept at constant temperature?
The volume can be decreased
How can the pressure of a gas be decreased whilst kept at constant temperature?
The volume can be increased
What effect does increasing temperature have on the pressure of a gas when held at constant volume?
Pressure of the gas will increase as the temperature increases
Why does pressure increase as temperature increases (constant volume)?
- Kinetic energy of molecules increases
- Collisions between molecules becomes more frequent
- Greater rate of change of momentum
- Greater force and therefore pressure
If gas A is at a low pressure, and gas B is at a high pressure, what can be said about the rate of collisions in each gas?
- There are more collisions per second in Gas B then in Gas A
- The rate of collisions is higher in Gas B
Describe the force that the pressure of a gas exerts on the walls of its container.
- The net force acts at right-angles to the container’s surface
- The magnitude of the force increases the pressure increases
Explain how increasing volume of a gas results in a decrease of pressure.
- Molecules become more spread out so collisions become less frequent
- This reduces the rate of collisions
- Rate of change of momentum decreases, and so force exerted on container
decreases, resulting in a lower pressure
What can be said about the product of pressure and volume for a fixed mass of gas at a constant temperature?
It is constant, p V = Constant
What increases when you do work on a gas?
- The internal energy of the gas
- This can also lead to an increase of temperature
What increases when you do work on a gas?
- The internal energy of the gas
- This can also lead to an increase of temperature
Why does the temperature of air inside a bike pump increase when it is pumped?
- Work is done on a gas when it is compressed
- Doing work on a gas increases its internal energy, so also increases the
average kinetic energy of the molecules - Temperature increases with an increase of average kinetic energy
Why does atmospheric pressure decrease as you move higher above the Earth’s surface?
The atmospheric pressyre at a point is equal to the weight of the air in the column above that point, as you move higher above the Earth the amount of air in said column decreases - resulting in less weight above and as a result less pressure at the point.
What does an object in a fluid experience as a result of pressure?
Forces at right angles to all of its surfaces.
