particle model pressure and specific heat Flashcards
What is the equation for density?
density (ρ) = mass (Kg) / volume (M³)
fluid
can be either a liquid or a gas.
Formula for pressure
Pressure (Pa) = Force (N) / Area (M²)
P=F/A
The unit of pressure is the pascal (Pa)
One Pa is equal to one N/M²
Pressure in a column of Liquid
As you move deeper in a liquid the pressure increases due to a greater weight of liquid above you.
The increase in pressure caused due to a column of liquid can be calculated with the equation:
pressure (Pa) =density (Kg/M³) ×gravitational field strength (N/Kg) ×height of column (M)
p= ρgh
Upthrust
The weight of fluid displaced by an object is equal to the upthrust acting on the object.
If an object is fully immersed the volume of fluid, it displaces is equal to its own volume.
A fully immersed object will float if the upthrust is greater than its weight, which is only true if the weight of the fluid displaced is greater than the weight of the object itself. The only way this can be true is if the density of the fluid is greater than the density of the object.
If an object is denser than the surrounding fluid it will sink
If an object is less dense than the surrounding fluid it will float
Atmospheric Pressure
Air molecules collide with a surface create atmospheric pressure.
At increasing altitude, the distance between air molecules increases.
So, the frequency of collisions of air molecules on the surface must decrease.
Which means that air pressure decreases with altitude.
boyle’s law
Boyle’s law states that for a fixed mass of gas held at constant temperature the product of the gas pressure and the volume occupied by the gas is equal to a constant.
The equation relates to Boyle’s Law is
pV = constant or 𝑝_1 𝑉_1 = 𝑝_2 𝑉_2
p = pressure - Pa
V = volume - M³
This means that gas pressure and volume are inversely proportional to each other (if temperature remains constant!)
Gas Pressure
When gas particles collide with the surface of the container they exert a force on the surface. The total force exerted on the container is determined by the number of collisions in a set amount of time and the force exerted by each collision. This net force is normal (perpendicular to) to the surface of the container. As a force is exerted on an area, the gas thus exerts a pressure on the sides of the container.
Temperature, Volume, and gas pressure
A container of gas is compressed. a then b
A container of gas is heated. c
More air is pumped into a bicycle tyre. b
- a) Volume decreases so / b) more air in a fixed volume / c) gas particles have more kinetic energy and move faster.
- Therefore, the frequency of collisions with the container wall increases.
- Also, the force exerted by each collision with the container wall increase.
- So, the total force exerted by the gas on the container walls increases.
Work Done on a gas
If a force compresses a gas work has been done on the gas (There is a transfer of energy to the gas).
When a gas is compressed it temperature increases as the gas molecules gain KE. E.g. when air in compressed into a bike tyre from a bike pump it becomes hotter.
When a gas expands its temperature decreases. E.g The gas from an aerosol deodorant feels cold.
specific heat capacity
The equation that links these together is:
∆E=mc∆θ
∆E = change in internal energy - J
∆θ = change in temp - °C
c = specific heat capacity - J/kg°C
m = mass - Kg
The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius.
specific latent heat
The equations relating to specific latent heat is:
E=mL
E = energy – (J)
m = mass (Kg)
L = specific latent heat – (J/Kg)
Specific latent heat of vaporisation refers to:
Liquid to Gas (or Gas to liquid)
Specific latent heat of fusion refers to:
Solid to Liquid (or Liquid to Solid)
The specific latent heat of a substance is the amount of energy required to change the state of one kilogram of the substance with no change in temperature.
