What is density?

A measure of the ‘compactness’ of a substance, relating its mass to how much space it takes up. It does not vary with size or shape.

How is density calculated?

Density = mass / volume

P = m / V

g/cm^3 or kg/m^3 = g or kg / cm^3 or m^3

How can you find the density of a solid?

Measure its mass using a balance. (M1)

Fill a bottle with a liquid of known density, place a stopper and dry the outside. Measure its mass. (M2)

Empty the bottle, put the object in, and repeat step 2. Measure its mass. (M3)

Find the mass of displaced water (M2 - (M3 - M1))

Find the volume displaced using the density formula. This equals the object’s volume.

Calculate density using the density formula.

What is kinetic theory?

A way of explaining matter using tiny balls to represent particles.

What are particles like in a solid?

Strong forces of attraction hold particles close together in a fixed, regular arrangement. Particles have little energy so can only vibrate in fixed positions.

What are particles like in a liquid?

Forces of attraction between particles are weaker. Particles are close together but can move past each other and form irregular arrangements. They have more energy so move in random directions at low speeds.

What are particles like in a gas?

There are almost no forces of attraction between particles. Particles have more energy than in liquids and are free to move. They travel in random directions at high speeds.

What are the names for the different changes of state?

Solid to liquid - melting Liquid to solid - freezing Liquid to gas - evaporating Gas to liquid - condensing Gas to solid - deposition Solid to gas - sublimation

What is water’s specific heat capacity?

4200 J/kg degreesC

What is specific heat capacity?

The amount of energy required to raise 1kg of a substance by 1 degree C.

What is the equation for specific heat capacity?

Change in thermal energy = mass x specific heat capacity x temperature change

Q = m x c x theta

J = kg x J/kg degreesC x degreesC

How can you find the specific heat capacity of water?

Use a balance to find the mass of the insulating container

Fill it with water and find the mass again, calculate the water’s mass

Use a power supply, a circuit, and an immersion heater to warm up the water. Use E = I x V x t to find the energy transferred over a set time

Measure the temperature change with a thermometer

Find the specific heat capacity

Why does temperature not change in a change of state?

Energy is used for breaking intermolecular bonds rather than raising the temperature

How can you see how a change of state affects temperature in ice?

Fill a beaker with crushed ice

Put a thermometer in and record the temperature

Use a Bunsen burner to gradually heat the beaker

Record the temperature and state of ice every 20 seconds

Continue this until the water starts to boil

Plot a graph of temperature against time

What is specific latent heat?

The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature

What are the two types of specific latent heat?

Latent heat of fusion - the latent heat for melting or freezing

Latent heat of vaporisation - the latent heat for evaporating or condensing

What is the equation for specific latent heat?

Thermal energy = Mass x Specific Latent Heat

Q = m x L

J = kg x J/kg

What creates gas pressure?

Gas particles move around at high speeds, colliding into other particles and things in the way. When they collide, they exert a force and so a pressure. In a sealed container, the outward gas pressure is the total force exerted by all of the particles in the gas on a unit area of the container walls.

What causes gas pressure to vary and why?

Temperature - higher kinetic energies of particles so more frequent and forceful collisions

Volume - particles get closer together and hit the walls more often

What is the equation linking pressure and volume?

P1V1 = P2V2

Pressure in Pa or N/m^2

Volume in m^3

What is absolute zero?

The temperature at which particles have as little energy in their kinetic stores as possible. It is -273 degrees C or 0 Kelvin

How can you change the pressure of a gas in a container?

Heat or cool it

Reduce or increase the volume e.g. in a syringe

How does doing work on a gas affect its temperature?

It can increase its energy, which increases its temperature. The gas exerts pressure and so a force and so work has to be done against it. This transfers kinetic energy to it, so increases the internal energy and so the temperature.

What is an elastic object?

An object that can be elastically distorted (goes back to its original shape and length after force is removed)

What is the elastic limit?

The point at which an object stops distorting elastically and begins to distort inelastically

What is the equation for the force on a spring?

Force = Spring constant x Extension F = k x x N = N/m x m

What does the graph of a spring’s extension look like?

It is linear up until the limit of proportionality, where the graph begins to flatten out. After this is the elastic limit, where the spring becomes permanently stretched.

How could you carry out the practical to investigate the link between force and extension in springs?

First do a pilot experiment with an identical spring: load it with masses and plot a force-extension graph. The line should stay straight for at least the first 6 masses, if not use smaller masses.

Actual experiment: measure the spring’s natural length, taking the reading at eye level. Put markers on the bottom and top of the string to make more accurate readings. Add a mass to the string and measure its new length; find the extension. Repeat this process and plot a force-extension graph.

What is the equation for energy/work done on a spring?

Energy = 1/2 x spring constant x extension^2 E = 1/2 x k x x^2 J = 1/2 x N/m x m^2

What is the equation for pressure?

Pressure = Force / Area P = F/A Pa = N/m^2

What is the equation for fluid pressure?

Pressure due to a column of liquid = height of the column x density of liquid x gravitational field strength

P = h x rho (like a p) x g

Pa = m x kg/m^3 x N/kg

What is upthrust the resultant force to?

Pressure, as pressure increases with depth, so pressure is greater on the bottom of an object than the top. Upthrust is the resultant force upwards.

What is upthrust equal to?

The weight of water displaced by the object

What makes objects float or sink?

If upthrust is equal to an object’s weight, forces balance and it floats. If an object’s weight is greater than upthrust, the object sinks, so it is to do with density. The denser the object, the more fluid is needed to be displaced for it to float. If it is denser than the fluid, it will sink,

What is the relationship between atmospheric pressure and height?

The higher you go, the less the atmospheric pressure, as the atmosphere is less dense, so fewer air molecules are colliding with the surface of the Earth. There are also fewer air molecules, so the weight of the air is less, which contributes to atmospheric pressure, so pressure is less.