# Physics: Unit Six

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A volume of one cubic meter of wood has a mass of about 800kg. But a cubic meter of concrete has a mass of about 2,400kg. So the density of concrete is about three times the density of wood.
density, p (kg/cm^) = mass, m (kg) / volume, V (m^)
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Objects that have a lower density than water (i.e.
P6.1 - Density
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P6.2 - States of matter
Solid: doesn't float, fixed shape, fixed volume, much higher density than gas.
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Liquid: does float, fits container shape, fixed volume, much higher density than gas.
Gas: does flow, fills container, volume can be changed, lower density than solid or liquid.
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Changes of state are examples of physical changes because no new substances are produced. If a physical is reversed, the substance recovers its original properties.
You can change the state of a substance by heating or cooling the substance.
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When a substance changes state, the number of particles in the substance stays unchanged. So the mass of the substance after the change of state is the same as the mass of the substance before the change of state.
The particles of a substance in its solid state are held next to each other in fixed positions. They vibrate about their fixed positions, so the solid keeps its own shape.
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The particles of a substance in its liquid state are in contact with each other. They move about at random. So a liquid doesn't have its own shape, and it can flow.
The particles of a shape in its gas state move about at random much faster than they do in a liquid. They are, on average, much further apart from each other than the particles of a liquid. So the density of a gas is much less than a solid/liquid.
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The particles of a substance in its solid, liquid, and gas states have difference amounts of energy. For a given amount of a substance its particles have more energy in gas than liquid state, and have more energy in liquid than solid state.
P6.3 - Changes of state
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For any pure substance undergoing a change of state, its temperature stays the same while the change of state is taking place.
The melting point of a solid and the boiling point of a liquid are affected by impurities in the substance.
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A beaker of ice below 0' heated slowly until water boils. The temperature of the water 1) increases until reaches 0' and when ice begins to melt 2) stays constant at 0' until all melted 3) increases to 100' where it boils 4) stays at 100' boiling
The energy transferred to a substance when it changes its state is called latent heat.
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Fusion is sometimes used to describe melting because different solids can be joined, or 'fused', together when they melt
The melting point of a pure substance is the same temperature at which it solidifies.
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The boiling point of a pure substance is the same temperature at which it condenses.
The flat section of a temperature-time graph gives the melting point or the boiling point of a substance.
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P6.4 - Internal energy
The energy stored by the particles of a substance is called the substance's internal energy. This is the energy of the particles that is caused by their individual motion and positions.
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The internal energy of the particles in a substance is the sum of: kinetic energy they have due to their individual motions relative to each other, and potential energy they have due to their individual positions relative to each other.
Internal energy does not include gravitational potential energy or the kinetic energy that is caused by the motion of the whole substance.
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When the temperature of a substance increases (or decreases) the total kinetic energy of its particles increases (or decreases).
When the physical state of a substance changes, the total potential energy of its particles changes.
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Solid - strong forces of attraction between particles keeping fixed positions; each particle vibrates about average fixed position; when a solid is heated, particles' energy stores increase and they vibrate more, or melts and sublimates if much more.
Liquid - forces of attraction weaker so no fixed shape, but strong enough to stop particles moving away completely; when heated, some particles gain enough energy to break away from others, and the molecules that escape from the liquid are a gases.
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Gas - forces of attraction are so weak they are insignificant; particles move at high speed in random directions, colliding with each other; when heated, particles gain energy and move faster, causing pressure to increase as there are more collisions
P6.5 - Specific latent heat
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Specific latent heat of fusion (Lf) of a substance is the energy needed to change the state of 1kg of the substance from solid to liquid, at its melting point (without changing its temp)
specific latent heat of fusion, Lf (J/kg) = energy, E (J) / mass, m (kg)
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Specific latent heat of vaporisation (Lv) of a substance is the energy needed to change the state of 1kg of the substance from liquid to vapor, at its boiling point (without changing its temp)
specific latent heat of vaporisation, Lv (J/kg) = energy, E (J) / mass, m (kg)
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The specific latent heat of ice (or water) can be measured using a low-voltage heater to melt the ice (or boil the water).
P6.6 - Gas pressure and temperature
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Increasing the tmeperature of any sealed gas container increases the pressure of the gas inside it. This is because: the energy transferred to the gas when heated increases the kinetic energy, and the average speed of molecules increase as a result
The pressure of a gas is caused by the random impacts of gas molecules on surfaces that are in contact with the gas.
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The unpredictable motion of smoke particles is evidence of the random motion of gas molecules.
P6.7 - Gas pressure and volume
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When gas is stored in a tube and a piston is pushed into the tube, the volume of air decreases as air is compressed. As long as the compression occurs slowly, the temperature of the air in the tube doesn't change.
If the volume of a fixed mass of gas at constant temperature is reduced, the gas pressure increases because:
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1) the space the molecules move in is smaller, so they don't travel as far between each impact with the surface of their container. 2) the molecules hit the surface more often, so the number of impacts per second increases.
pressure, p (Pa) x volume, V (m^) = constant
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The temperature of a gas can increase if it is compressed rapidly because work is done on it and the energy isn't transferred quickly enough to its surroundings.
P6: Molecules and matter
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A wooden post has a volume of 0.025m^ and has a mass of 20kg. Calculate the density in kg/m^.
density = mass / volume. = 800kg/m^.
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A measuring cylinder contained a volume of 120cm^ of a particular liquid. The liquid was then poured into an empty beaker of mass 51g. The total mass of the breaker and the liquid was then found to be 145g. Calculate the mass of the liquid in grams.
mass of liquid = 145 - 51. = 94g.
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A measuring cylinder contained a volume of 120cm^ of a particular liquid. The liquid was then poured into an empty beaker of mass 51g. The total mass of the breaker and the liquid was then found to be 145g. Calculate density of the liquid in kg/m^.
density = mass / volume. = 780kg/m^.
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In a chemistry experiment, 0.00020m^ (= 200cm^) of gas was collected in a flask at a pressure of 125kPa. Calculate the volume of this mass of gas at a pressure of 100kPa and the same temperature.
250cm^.
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## Other cards in this set

### Card 2

#### Front

Objects that have a lower density than water (i.e.

P6.1 - Density

### Card 3

#### Front

P6.2 - States of matter

### Card 4

#### Front

Liquid: does float, fits container shape, fixed volume, much higher density than gas.

### Card 5

#### Front

Changes of state are examples of physical changes because no new substances are produced. If a physical is reversed, the substance recovers its original properties.