Physics Chapter on Density and Brownian Motion

Study Notes

Matter is anything that has mass and takes up space
All matter is made up of particles
The main points of particle theory are summarized in the particle theory
Particle theory:
- All matter is made up of particles
- Particles are very small
- There are empty spaces between particles
- Particles are moving all the time
- Different matter is made up of different particles
- Different particles have different sizes and masses
Scientists have used experiments to support the particle theory
Atoms are the basic types of particles that make up matter
Molecules consist of two or more atoms joined together chemically
A chemical formula of a molecule shows the types and the number of atoms in a molecule.
- For example: H₂O (water molecule)

Matter exists in three states: solid, liquid, and gas
These states have different properties
Solids:
- Have a fixed shape
- Cannot be compressed readily
Liquids:
- Do not have a fixed shape
- Take on the shape of their container
- Cannot be compressed readily
Gases:
- Do not have a fixed shape
- Take on the shape of their container
- Can be compressed readily

When a solid dissolves in water, the solid's particles separate and mix with the water particles
The resulting mixture is a solution.
The dissolved substance is called the solute. Water is the solvent in this case.
The mass of the resulting solution is equal to the combined mass of the solute and solvent.
- Volume of the solution may be slightly smaller than the combined volume of the solute and solvent, due to space between particles.

Heating causes particles to move faster and spread out further, which increases the size of a substance. This is called thermal expansion.
Cooling causes particles to move slower and come closer together, which decreases the size of a substance. This is called thermal contraction.

Gas pressure is caused by gas particles hitting the walls of the container.
Gas pressure increases with temperature as particles move faster and hit the container walls more often.
Gas pressure increases when the volume (space) of the container is decreased as gas particles hit the container walls from a smaller space more frequently.

Density: mass per unit volume
- Density = mass / volume (in g/cm³ or kg/m³)
Objects with higher density have more mass for a given volume.
Whether objects float or sink depends on their density compared to the liquid they are in.
- Objects with lower densities will float, objects with higher densities will sink.