P1.3 Flashcards
Pressure formula
p = 𝐅/𝐀
Pressure - Pa (pascals)
Why do gases exert a pressure
Particles of a substance in the gas state, move about at high speed, in random directions.
The particles collide with each other,and with the walls of the container.
A gas exerts a pressure, due to the force with which particles collide with the container walls, over a given surface area.
Temperature and gas pressure
The higher the temp, the greater KE, the particles collide more often and with a greater force with walls - greater pressure
Relationship between gas pressure and temperature
There is a directly proportional relationship between temp and pressure, at a constant volume
Relationship between pressure and volume
Pressure and volume are inversely proportional at a constant temp
(Volume doubles = pressure halves)
Why is there an inversely proportional relationship
If you half the volume…
Number of collisions with particles/ container walls doubles
The force exerted per unit time doubles
Pressure of gas doubles
Equation for pressure and volume
pressure (Pa) x volume (m3) = constant
p1 x V1 = p2 x V2
What happens when a gas is compressed
… a force is required to move the gas particles together
… work is done on the gas… gas particles gain kinetic energy… gas particles move faster.
… gas temperature increases.
What happens when a gas expands
… a force is applied by gas particles together
… work is done by the gas… gas particles lose kinetic energy… gas particles move slower.
… gas temperature decreases.
Why do you need to wait before taking a reading of the pressure, after changing the volume
As the volume of the gas was changed, work would have been done on or by the gas.
This would change the temperature of the gas, which would affect the pressure.
Why can earth maintain an atmosphere
Due to its gravitational field
Model of the atmosphere
- made up of a single layer
- the density is the same without
What is the atmospheric pressure
100,000
Atmospheric pressure and altitude
Atmospheric pressure decreases the higher you travel, owing to fewer gas particles, due to a weaker gravitational field.
Why does a balloon expand when it rises
As you travel higher into the Earth’s atmosphere, air pressure decreases.
This is because the Earth’s gravitational field becomes weaker with height, thus fewer gas particles are held onto.
This decrease in pressure outside the balloon, results in a net outward pressure that expands the balloon.
What does liquid pressure depend on
Depth below the surface
Independent of container shape + surface area
Pressure and density
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.
Thus, the greater the depth, the more mass (per unit area) and weight of water, the greater the pressure.
Similarly, the greater the density, the more mass (per unit area) and weight of water, the greater the pressure.
Liquid pressure equation
p = ρgh
P - pressure - pascals
ρ - density - kg/m squared
g - gravitational field strength - n/kg
h - depth - meters
Liquid pressure difference
p = ρg∆h
What does upthrust result from
A pressure difference between the top and bottom of the fluid
The upthrust experienced by a body is…
Equal to the weight of the fluid
Upthrust formula
Upthrust = density of fluid X surface area X depth submerged X g
Less dense bodies
Rise
If the weight of the body is more then the upthrust
The body sinks
For a body immersed within a fluid if
Weight = upthrust
Weight > upthrust
Weight
Weight = upthrust
- body will float
Weight > upthrust
- body will sink
Weight < upthrust
- body will rise
A body made of a given substance will float only if…
it is able to acquire enough upthrust (displace enough fluid) before becoming fully submerged
Bodies with a large surface area when submerged
Only submerge to a small depth
i.e. large SA means small depth because formula is upthrust = density X g X SA X H, in which SA X H = volume
