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I/GCSE Physics - Solids, Liquids and Gases

 Topic 5: Solids, Liquids and Gases

July 5, 2021

Solids, Liquids and Gases Summary

Density

Density (ρ) = mass (m) / volume (v)

  • When it comes to I/GCSE physics, Density is how much there is in a given volume.
  • Density is measured in kg/m3, although it is sometimes more convenient to measure it in g/cm3, in which case, divide it by 1000 to get Kg.

For example, the density of water is 1g/cm3, this is the same as 0.001kg/cm3

For a regular solid

  • Find the volume (volume = width x height x depth) in cm3
  • Find the mass
  • Divide the mass by the volume

For a liquid

  • Find the mass (m) by weighing a dry cylinder (M1), and then with the liquid in it (M2) and then find m = M2 - M1
  • Use the cylinder to find the volume- it will be in cm3
  • Divide the mass by the volume.

Pressure

Pressure (p) = Force (F) / Area (A)

  • Force is measured in Newtons (N) and Area is measure in Metres2 (m2))
  • Pressure is measured in either Pascals (Pa) or in Newtons per metre (N/m2). Remember that 1 Pa = 1 N/m2
  • Solid objects exert downwards pressure upon where they stand.
  • The smaller the surface area, the greater the pressure.
  • In stationary liquids and gases, pressure at any point acts in all directions and increases with the depth of the gas or liquid (as it has the mass of the liquid/gas on top of it, which makes it heavier, and so a greater pressure). A difference in pressure between two places in a fluid will result in a flow of the fluid from the place at higher pressure to the place of lower pressure

Pressure and Depth

Pressure difference (p) = Height (m) x density (kg/m3) x Gravitational field strength* (N/Kg)

*On Earth, this is 10N/Kg

The States of Matter

  • Molecules in a solid are tightly packed and held in fixed positions by strong forces. The molecules vibrate around their fixed positions. As the solid gets hotter, these vibrations get bigger.
  • Molecules in a liquid are closely packed but do not have a regular structure. The forces between the molecules are strong, but the molecules can move randomly. It is a fluid.
  • Molecules in a gas are widely spread and in a continuous state of random motion. The forces between the molecules are weak, except during collisions. The molecules move randomly and gases are fluids.

Brownian motion

  •  Brownian studied that pollen grains in water will move around randomly.
  • The particles in matter (i.e. molecules) are extremely small and in fluids they are in a continuous state of rapid random motion.
  • A gas exerts a pressure on objects, for example, the walls of its container, as a result of continuous collisions between the gas molecule and its container. Each individual collision of many millions of molecules colliding per second will result in a significant pressure.
  • The random motion of gas and liquid particles explains why pressure acts in all directions at any point.
  • The speed if molecules increases with temperature, so as we heat gases in a rigid container, more energetic collisions with the walls occur more frequently, so the pressure increases.
  • The temperature of the gas in Kelvin is proportional to the average kinetic energy of the gas molecules.
The Gas Laws
  • The gas laws refer to the behaviour of fixed amounts of gas.
  • The following properties of a fixed amount of gas change with respect to one another: volume, pressure and temperature.
  •  Boyles law= P1 x V1 = P2 x V2
  • This law shows that volume is inversely proportional to pressure- if you double the volume of a gas, the pressure halves.
  • This law only works if it has a fixed temperature.
  • For a fixed amount of gas at a constant volume- P1/T1 = P2/ T2

Absolute Zero

  • Absolute zero is the lowest temperature you can get because it has a pressure of zero- there are no vibrations whatsoever.
  • In degrees celcius, this is -273C
  • In Kelvin, this is 0K
  • To convert C to K, add 273
  • To convert K to C, subtract 273

 References:

  1. https://getrevising.co.uk/resources/igcse_solids_liquids_and_gases
  2. https://images.topperlearning.com/topper/tinymce/imagemanager/files/78e3fa4ae14a96b3150ae3d43412d5a05d15ee1bce2070.97957575Brownianmovement.png
  3.  http://2.bp.blogspot.com/-ewDon8v1bnI/U02RL9O3uAI/AAAAAAAAABY/3MeaR0wxSlE/s1600/CL+Double.png
  4. https://wps.prenhall.com/wps/media/objects/943/966268/images/aabjusaa.jpg

And we're all done for today! 

Drafted by Kin (Physics)

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