The Ultimate
IGCSE Physics
Notes
,Unit 1: Solids, Liquids and Gases
Density
SO what’s density? Well, all solids, liquids and gases have different properties and characteristics. One such characteristic is
density. Solids are often very dense, liquids are less dense than solids, and gases have very low densities. Density is how much
mass something has for a certain volume – in other words, how ‘squashed up’ something is.
To calculate density, use this equation:
Density = Mass/Volume
P = m/v
Example: A piece of iron has a mass of 390kg and a volume of 0.05m3. What is its density?
P = m/v
P = 390kg/0.05m3
= 7800kg/m3 Remember the unit! Density can be kg/m3, g/cm3…etc
Calculating Volumes for the Density
For a cuboid like this, simply multiply its length, width and height. I’m assuming you know this, but if
not, work up your maths man…
As for irregular solids, measure out a certain amount of water
with a measuring cylinder. This is the control (something to
compare results to). Do the same with another measuring
cylinder, and drop the solid in. Note the rise in the level of
water. The difference between the two measurements is the
volume of the solid, in this case, 10ml.
Pressure
Pressure in Solids
Lets start like this: You can easily push a pin into a piece of wood quite easily, but it is pretty much impossible to make a hole in
the wood with your finger. You can try with little success (and end up with splinters all over your fingers). Why is that? The
small point of the drawing pin concentrates all your pushing force into a tiny area, so the pin goes into the wood easily.
To get to the point, pressure is defined as the force per unit area. Force is measured in newtons (N) and area is measured in
square metres (m2). The unit for pressure is N/m2 or Pa (for Pascals).
Unfortunately, there is an equation that comes with pressure and this is ONLY FOR SOLIDS:
Pressure (in Pascals) = Force (in newtons)/Area (in square metres)
p = f/a
Example: A woman weighs 600N and the total area of her shoes in contact with the ground is 0.0015m2. Find the pressure she
is exerting to the ground.
p = f/a
p = 600N/0.0015m2
= 400000Pa (or 400kPa)
Pressure in Liquids and Gases
,Pressure in liquids act equally in all directions as long as the liquid is not moving. This is the same for gases. The pressure in air is
a staggering 100000Pa, but since the pressure inside our bodies are similar, we don’t feel the pressure. The pressure in air is
also referred to as 1.0 atmosphere.
To calculate pressure in liquids use the following equation:
Pressure (in Pa) = Height/Depth (in m) x Density (in kg/m3) x Gravitational Field Strength (in N/kg)
Or p = hdg Note that g is usually 10N/kgv
Example: Justin Bieber’s (oh my god!) swimming pool has a depth of 3m. What is the total pressure of the swimming pool? Take
the gravitational field strength to be 10N/kg and the density of water to be 1kg/m 3 (ignore the swimming pool being
chlorinated ‘cause JB’s swimming pool is always clean anyways).
p = hdg (the actual equation is p=hpg, but I’m not bothered finding that special p for density)
p = 3m x 1kg/m3 x 10N/kg
p = 30Pa
The Brownian Motion
Brownian Motion: The continual random movement of microscopic particles. When particles collide into one another, this
causes a change in speed and direction of the particles, making them randomly move about.
Boyle’s Law
This is all summarized into the following equation:
Pressure1 x Volume1 = Pressure2 x Volume2
Or p1V1 = p2V2
Example: Atmospheric pressure is 100kPa. Some air in a sealed container has a volume of 2m3 at atmospheric pressure. What
would be the pressure of the air if you reduced its volume to 0.2m3?
100kPa = 100000Pa
P1V1 = p2V2
100000Pa x 2m3 = p2 x 0.2m3
200000 = 0.2p2
P2 = 1000000Pa
= 1000kPa
And in words…
Boyle’s Law: At a constant temperature and with a fixed mass of gas, pressure is inversely proportional to volume.
Question: How does a gas exert a pressure on the walls of its container?
Billions of tiny air particles move about in continual random motion. Particle collisions with the walls of the container exerts a
force, which gets distributed over the area of the wall of the container, hence, exerting a pressure.
Pressure Law
Temperature also has an effect on the pressure of a gas. This is shown in an
experiment set up on the right. When water is heated gradually, the air is also heated,
changing the reading on the pressure gauge. Plot down the results and you’d get a
graph that looks something like this.
, Wait a minute…shouldn’t the pressure be at zero pascals? No.
This is because pressure is NOT proportional to temperate in
Celsius. But what happens if you continue cooling the gas? You’d
find that when pressure is zero, the temperate would be at -
2730C. This temperate is known as absolute zero. When converted
to kelvins (another type of measurement for temperature),
absolute zero is zero kelvins. But back to the point, what would
happen if you converted the temperatures into kelvins?
Converting between Kelvins and Celsius
Kelvins = Celsius + 273
Celsius = Kelvins – 273
If you convert the temperatures into kelvins, this is what happens:
There is a positive correlation! This shows that pressure of gas is
proportional to temperature in Kelvin. This leads into the Pressure Law
equation: (Note that temperatures must be in Kelvin)
Pressure1/Temperature1 = Pressure1/Temperature1
Or p1/T1 = p2/T2
Example: You take an empty tin and put the lid on tightly. You heat it
using a Bunsen burner until the temperature of the air inside is 500C.
What is the pressure of the air inside the tin? The temperature of the
room is 200C and atmospheric pressure is 100kPa.
We must first convert the temperature in Kelvin, so:
T1 = 20 + 273 = 293K (This is the temperature OUTSIDE the
tin)
T2 = 50 + 273 = 323K (This is the temperature INSIDE the tin)
p1/T1 = p2/T2
100kPa/293K = p2/323K
p2 = 110kPa
Now to summarise the Pressure Law:
Pressure Law: With a fixed mass of gas at a constant volume, pressure is proportional to temperature (in Kelvins).
States of Matter
Solids Liquids Gases
Particles are closely packed. Particles are closely packed. No fixed positions.
Regular structure. Irregular structure. Move at rapid random motion.
Vibrate about fixed positions. Random motion within structure. Are very spread out.
Change in States of Matter
IGCSE Physics
Notes
,Unit 1: Solids, Liquids and Gases
Density
SO what’s density? Well, all solids, liquids and gases have different properties and characteristics. One such characteristic is
density. Solids are often very dense, liquids are less dense than solids, and gases have very low densities. Density is how much
mass something has for a certain volume – in other words, how ‘squashed up’ something is.
To calculate density, use this equation:
Density = Mass/Volume
P = m/v
Example: A piece of iron has a mass of 390kg and a volume of 0.05m3. What is its density?
P = m/v
P = 390kg/0.05m3
= 7800kg/m3 Remember the unit! Density can be kg/m3, g/cm3…etc
Calculating Volumes for the Density
For a cuboid like this, simply multiply its length, width and height. I’m assuming you know this, but if
not, work up your maths man…
As for irregular solids, measure out a certain amount of water
with a measuring cylinder. This is the control (something to
compare results to). Do the same with another measuring
cylinder, and drop the solid in. Note the rise in the level of
water. The difference between the two measurements is the
volume of the solid, in this case, 10ml.
Pressure
Pressure in Solids
Lets start like this: You can easily push a pin into a piece of wood quite easily, but it is pretty much impossible to make a hole in
the wood with your finger. You can try with little success (and end up with splinters all over your fingers). Why is that? The
small point of the drawing pin concentrates all your pushing force into a tiny area, so the pin goes into the wood easily.
To get to the point, pressure is defined as the force per unit area. Force is measured in newtons (N) and area is measured in
square metres (m2). The unit for pressure is N/m2 or Pa (for Pascals).
Unfortunately, there is an equation that comes with pressure and this is ONLY FOR SOLIDS:
Pressure (in Pascals) = Force (in newtons)/Area (in square metres)
p = f/a
Example: A woman weighs 600N and the total area of her shoes in contact with the ground is 0.0015m2. Find the pressure she
is exerting to the ground.
p = f/a
p = 600N/0.0015m2
= 400000Pa (or 400kPa)
Pressure in Liquids and Gases
,Pressure in liquids act equally in all directions as long as the liquid is not moving. This is the same for gases. The pressure in air is
a staggering 100000Pa, but since the pressure inside our bodies are similar, we don’t feel the pressure. The pressure in air is
also referred to as 1.0 atmosphere.
To calculate pressure in liquids use the following equation:
Pressure (in Pa) = Height/Depth (in m) x Density (in kg/m3) x Gravitational Field Strength (in N/kg)
Or p = hdg Note that g is usually 10N/kgv
Example: Justin Bieber’s (oh my god!) swimming pool has a depth of 3m. What is the total pressure of the swimming pool? Take
the gravitational field strength to be 10N/kg and the density of water to be 1kg/m 3 (ignore the swimming pool being
chlorinated ‘cause JB’s swimming pool is always clean anyways).
p = hdg (the actual equation is p=hpg, but I’m not bothered finding that special p for density)
p = 3m x 1kg/m3 x 10N/kg
p = 30Pa
The Brownian Motion
Brownian Motion: The continual random movement of microscopic particles. When particles collide into one another, this
causes a change in speed and direction of the particles, making them randomly move about.
Boyle’s Law
This is all summarized into the following equation:
Pressure1 x Volume1 = Pressure2 x Volume2
Or p1V1 = p2V2
Example: Atmospheric pressure is 100kPa. Some air in a sealed container has a volume of 2m3 at atmospheric pressure. What
would be the pressure of the air if you reduced its volume to 0.2m3?
100kPa = 100000Pa
P1V1 = p2V2
100000Pa x 2m3 = p2 x 0.2m3
200000 = 0.2p2
P2 = 1000000Pa
= 1000kPa
And in words…
Boyle’s Law: At a constant temperature and with a fixed mass of gas, pressure is inversely proportional to volume.
Question: How does a gas exert a pressure on the walls of its container?
Billions of tiny air particles move about in continual random motion. Particle collisions with the walls of the container exerts a
force, which gets distributed over the area of the wall of the container, hence, exerting a pressure.
Pressure Law
Temperature also has an effect on the pressure of a gas. This is shown in an
experiment set up on the right. When water is heated gradually, the air is also heated,
changing the reading on the pressure gauge. Plot down the results and you’d get a
graph that looks something like this.
, Wait a minute…shouldn’t the pressure be at zero pascals? No.
This is because pressure is NOT proportional to temperate in
Celsius. But what happens if you continue cooling the gas? You’d
find that when pressure is zero, the temperate would be at -
2730C. This temperate is known as absolute zero. When converted
to kelvins (another type of measurement for temperature),
absolute zero is zero kelvins. But back to the point, what would
happen if you converted the temperatures into kelvins?
Converting between Kelvins and Celsius
Kelvins = Celsius + 273
Celsius = Kelvins – 273
If you convert the temperatures into kelvins, this is what happens:
There is a positive correlation! This shows that pressure of gas is
proportional to temperature in Kelvin. This leads into the Pressure Law
equation: (Note that temperatures must be in Kelvin)
Pressure1/Temperature1 = Pressure1/Temperature1
Or p1/T1 = p2/T2
Example: You take an empty tin and put the lid on tightly. You heat it
using a Bunsen burner until the temperature of the air inside is 500C.
What is the pressure of the air inside the tin? The temperature of the
room is 200C and atmospheric pressure is 100kPa.
We must first convert the temperature in Kelvin, so:
T1 = 20 + 273 = 293K (This is the temperature OUTSIDE the
tin)
T2 = 50 + 273 = 323K (This is the temperature INSIDE the tin)
p1/T1 = p2/T2
100kPa/293K = p2/323K
p2 = 110kPa
Now to summarise the Pressure Law:
Pressure Law: With a fixed mass of gas at a constant volume, pressure is proportional to temperature (in Kelvins).
States of Matter
Solids Liquids Gases
Particles are closely packed. Particles are closely packed. No fixed positions.
Regular structure. Irregular structure. Move at rapid random motion.
Vibrate about fixed positions. Random motion within structure. Are very spread out.
Change in States of Matter
