P1.2 Density

Density is equal to mass divided by volume

p = m/v

p is density, m is mass, v is volume

Upthrust: an object floats in a fluid if the density of the object is lower than the density of the fluid. The force that keeps the object afloat is called upthrust.

Law of displacement: it says that an object completely submerged in a fluid will replace an amount of fluid equal to its own volume.

Solids: a fixed shape due to the strong forces between its particles. cannot be compressed because their particles are already very close together and cannot flow. The particles in a solid are arranged in an ordered pattern. The particles in a solid move around a fixed point

Liquids: cannot be compressed because their particles are already very close together. in a liquid the particles are in contact with one another but they cant still move. this allows a liquid to flow and take the shape of its container. Particles in a liquid are arranged in a disordered pattern.

Gases: can be compressed because their particles are very far apart. when water evaporate to become steam (gas) its volume increases by 1000x. The particles in a gas are free to move in any direction. because of this, a gas can flow, has no fixed shape and completely fills its container. the particles in a gas move randomly and are not organised in any way.

Solids= most dense and packed tightly together

Liquids = less dense than solids but more than gases, particles can move around each other

Gases = least dense and the particles are free to move with tiny forced between them.

for measuring the density of liquids, place a measuring cylinder on a balance and set the reading to zero. Pour the liquid into the cylinder and write down its mass and volume. Then calculate density

For solids we can use the law of displacement to estimate its volume. this is done using a displacement can or a graduated measuring cylinder. the volume of displaced water is measured an this is the volume of the object.

Changes of state: when a material changes state, it is able to recover its old properties if the change is reversed, some chemical reactions are also reversible. However some chemical reactions are irreversible - will not be able to return to its original properties

Melting - solid to liquid: if we heat a solid, the solid particles vibrate more energetically until they have enough energy to overcome the forced between them. This is when the solid melts. the temperature needed for this to happen is the melting point. Also sometimes called fusion

Boiling - liquid to gas: If we heat a liquid, the liquid particles move more energetically until they have enough energy to escape completely from the forced between them. The particles become a gas and move completely freely. The temp needed for this to happen is the boiling point. can also be called vaporisation

Condensation - gas to liquid: when the temp of a gas decreases to the boiling point, the strength of the forces between particles increases and the particles condense to become a liquid. for the same material its boiling point is the same as its condensing point.

Solidifying - liquid to solid: when the temp of a liquid decreases to the melting point, the strength pf the forces between particles increases and the liquid solidifies to become a solid. For the same material, its melting point is the same as its freezing point.

When a substance changes state, its mass is conserved