Physics U5 - Solids, Liquids and Gases

What is density, its formula and its unit of measurement?

• Density is how much matter is in a volume

• Measured in Kilograms per metre cubed (kg/m³)

• Density = mass / volume

Describe how to find the density of a liquid

• Measure the mass of a measuring cylinder using a beaker

• Add a liquid to the beaker and measure the new mass

• Subtract the new mass from the mass of the beaker to find the mass of the liquid

• The volume can be found by reading the reading on the cylinder

  • Ensure your eyes are level with the surface of the water in the cylinder to avoid parallax error

• Use the equation :

  • Density = Mass / Volume

Describe how to find the density of a solid. Refer to both regular and irregular shapes

• Find the mass of the solid by placing it on an electronic balance

• Measure the volume of the shape

  • If it is a regular shape, use a ruler to find the dimensions and mathematically calculating the volume

  • If it is an irregular shape, measure the reading on a measuring cylinder filled with water. Now add the object and measure the new reading. Subtract the new reading from the old one to find the volume

• Now find the density using the equation:

  • Density = mass / volume

Define pressure, its unit of measurement and its equation

• Pressure is the force per unit area

• Measured in Pascals (Pa)

• Pressure = force / area

Compare lying down on a bed of nails compared to a single nail

• Pressure is force per unit area

• The pressure depends on the weight of the person

• The more the weight, the higher the pressure because there’s a greater force

• The more the area of contact, the less pressure

  • Lying on a bed of nails means there is more contact area, the pressure is less

  • On one nail, all the pressure is concentrated to one spot

• A nail bed is safer, its less likely to cause injury

How is pressure distributed in a fluid?

Pressure at a point in a gas or liquid at rest acts equally in all direction and causes a force at right angles to any surface

What is the equation for the pressure of a fluid at a certain depth

Pressure = density x gravitational force of attraction x height

What factors affects the pressure beneath a liquid’s surface?

• Depth

  • The deeper you go, the more the pressure increases

    • This is because the pressure of the layers of water above accumulates as the height increases

• Density

  • The denser the liquid, the more the pressure

    • This is because there are more particles in the same volume and they collide more often to create more pressure

• Gravitational field strength

  • The greater the GFE, the more the pressure

    • This is because there is more attraction towards the

Explain how gas molecules exert pressure

• Gases move randomly and rapidly

• They collide with each other and the walls of their containers

• When they rebound, they change direction. This means that their velocity and therefore momentum changes.

• This means that they exert a force (force = change in momentum / time)

What is the equation linking force, momentum and time?

Force = change in momentum / time

Why does increasing the temperature increase the pressure?

• Particles gain thermal energy

• TE is converted into Kinetic energy

• Particles move faster

• They collide more often and more vigorously with each other and the walls of their container, increasing the pressure

What is absolute zero?

• Temperature at which pressure is zero

• - 273^oC

• 0K (Kelvin)

State the equation linking temperature in kelvin, temperature in Celsius and absolute zero

Temperature in Kelvin = Temperature in degrees Celsius + 273

What is the equation linking pressure and Temperature in gases?

P₁ = P₂

^{T₁ T₂}

State Boyle’s law

• P₁V₁ = P₂V₂

• At a constant temperature, if the volume increases, the pressure decreases cause molecules collide less frequently with the walls and each other

• In less volume, the particles are closer together so they collide more often, increasing the pressure

What is the relationship between Kelvin and Kinetic energy

• The temperature in Kelvin of a gas is directly proportional to the average kinetic energy of the molecules

What is Brownian motion?

Random motion of particles in a fluid