P1.3 - Pressure Flashcards
How do gas particles move?
- Particles of a substance in the gas state, move
about at high speed, in random directions - Random, Equally in all directions
What happens when gas particles are in a container?
The particles collide with each other, and with the walls of the container and exert a pressure.
Why do gases exert a pressure?
A gas exerts a pressure due to the force with which particles collide with the container walls, over a given surface area.
Define temperature.
Temperature is a measure of the average kinetic energy of particles in a substance.
Explain the relationship between gas pressure and temperature.
There is a directly proportional relationship between the temperature of a gas and its pressure, at a constant volume.
Why does an increase in temperature increase gas pressure and what assumptions are made?
- Assuming that the volume is constant, an
increase of temperature means the particles
have a higher average speed. - They will collide more frequently with the sides
of the container which results in a bigger force
over a certain area per unit time. - This results in a bigger pressure.
What does extrapolation show?
- Extrapolation shows the estimate of what would
happen if you continued to change the
independent variable. - It is a dotted line.
What happens to the gas pressure when the volume of a container halves? Explain.
- As the volume halves, the pressure doubles.
- If you halve the volume of a container, the number
of collisions of particles with the container walls
doubles and force exerted by the gas particles per
unit time doubles. - Therefore the pressure of the
gas doubles.
Describe the relationship between pressure and volume.
If temperature is constant, pressure and volume are inversely proportional.
What are the two equations linking pressure and volume?
- Pressure (Pa) x Volume (m3) = constant
- p1V1 = p2V2 (the product of pressure and volume of a gas is the same, before and after a change)
What happens when a gas is compressed?
- When a gas is compressed, a force is required
to move the gas particles together. - Work is done on the gas particles.
- Gas particles gain kinetic energy. The gas
particles move faster. - And hence, the gas temperature increases
What happens when a gas expands?
- When a gas expands, a force is applied by gas
particles together. - Work is done by the gas.
- The gas particles lose kinetic energy and the
particles move slower. - Gas temperature decreases
What is the simple model of the Earth’s atmosphere?
- A single layer of gas that surrounds the Earth with
a height of around 700km. - In this simple model, the density of the layer is the
same throughout, top to bottom
Why can the Earth maintain an atmosphere?
The Earth can maintain an atmosphere, due to its gravitational field strength.
What is atmospheric pressure and what is the atmospheric pressure at the surface of the Earth?
- Atmospheric pressure is pressure exerted by
gases of the atmosphere. - Atmospheric pressure (at sea level) is large at
around 100,000 Pa = 100kPa
What happens to atmospheric pressure as you go up and why?
As you go away from the surface of the Earth the atmospheric pressure decreases, owing to fewer gas particles exerting a force, due to a weaker gravitational field.
What does the liquid pressure in a container depend on?
The pressure in a liquid container only depends upon the depth below the surface.
What is liquid pressure independent to?
The pressure is independent of the container shape and surface area.
What does liquid pressure at a certain depth depend on?
The pressure at any given depth in a liquid in a container, is determined by the weight of the water above that must be supported.
What happens to liquid pressure in relation to depth?
The greater the depth, the more mass (per unit area) and weight of water, the greater the pressure.
What happens to liquid pressure in relation to density?
The greater the density, the more mass (per unit area) and weight of water, the greater the pressure.
What is the liquid pressure equation?
Pressure (Pa) = Height of column (m) x Density of liquid (kg/m3) x gravitational field strength (N/kg)
What is the liquid pressure equation (difference in height)?
Pressure (Pa) = Density x Gravitational field strength x Difference in height
When does the force of upthrust occur?
The force of upthrust occurs whenever a body is immersed (fully or partially) within a fluid.
What does upthrust result from?
Upthrust results from the pressure difference that exists between the top and bottom of the object.
What is upthrust equal to?
The upthrust experienced by a body is equal to the weight of the fluid displaced.
How can you tell is an object is floating (equation)?
An object floats if:
(pressure at bottom x area at bottom) - (pressure at top x area at top) = weight
What is the equation for upthrust?
- Upthrust = Weight of fluid displaced
- Upthrust = (mass of fluid) x g
- Upthrust = (density of
fluid) x (volume) x g - Upthrust = (Density of fluid) x (Surface area) x
(Depth submerged) x g - Upthrust = pghA
When will a body only float?
A body made of a given substance will float only if it is able to acquire enough upthrust before becoming fully submerged.
