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**Density **

Density (ρ) = mass (m) / volume (v)

- Density is how much there is in a given volume.
- Density is measured in kg/m
^{3}, although it is sometimes more convenient to measure it in g/cm^{3}, in which case, divide it by 1000 to get Kg.

For example, the density of water is 1g/cm^{3}, this is the same as 0.001kg/cm^{3 }

**For a regular solid**

- Find the volume (volume = width x height x depth) in cm
^{3} - Find the mass
- Divide the mass by the volume

**For a liquid**

- Find the mass (m) by weighing a dry cylinder (M
_{1}), and then with the liquid in it (M_{2}) and then find m = M_{2 }- M_{1} - Use the cylinder to find the volume- it will be in cm
^{3} - Divide the mass by the volume.

**Pressure **

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

- Force is measured in Newtons (N) and Area is measure in Metres
^{2}(m^{2)})

- Pressure is measured in either Pascals (Pa) or in Newtons per metre (N/m
^{2}). Remember that 1 Pa = 1 N/m^{2} - 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/m^{3}) 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= P
_{1}x V_{1}= P_{2}x V_{2} - 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- P
_{1}/ V_{1}= P_{2}/ V_{2}

This is often seen in I/GCSE Chemistry too! 👩🏫

**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 Celsius, this is -273C
- In Kelvin, this is 0K
- To convert C to K, add 273
- To convert K to C, subtract 273

References:

https://www.theschoolrun.com/what-are-states-of-matter

https://en.wikipedia.org/wiki/Brownian_motion

This is the end of the topic! Well done!

Drafted by Cherry (Chemistry)