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.
Pressure in a fluid ___________ with depth. Why?
- Increase
- The deeper you go, the greater the weight of water above you, and so a higher force and pressure
Pressure in a fluid ___________ with depth. Why?
- Increase
- The deeper you go, the greater the weight of water above you, and so a higher force and pressure
What equation is used to calculate the pressure at a given depth of liquid?
Pressure = depth x liquid density x gravitational field strength
What is upthrust?
The upwards force that an object experiences in a fluid as a result of a greater pressure below the object than above it.
Under what circumstances will an object float?
When the object’s upthrust equals its weight
Under what circumstances will an object sink?
When the object’s weight is greater than the upthrust.
When you submerge an object in a liquid, what is the upthrust acting on the object equal to?
The weight of the volume of liquid displaced as it is submerged.
What can be said aboutthe density of an object that sinks in water?
The object’s density is greater than the density of the water.
