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Solids, Liquids and GasesSyllabusTitleLesson 01: DensityLesson 02: Brownian MotionLesson 03: Pressure, Temperature and Volume


Solids, Liquids and Gases


Aims:• To experimentally find the density of different materials• To calculate the density of different materials

Starter:Which has more mass honey or beer?

Density 19/04/23


DensityDefinition:

Density is a measure of how much mass of a substance is contained in a fixed volume.

Symbol: ρ (rho)

Equation: ρ =m or m = V ρ

VMnemonic:

my violent rhinoUnits:

kg/m3

m

Vρ


What is the Mass of Air in the Room? make a guess Then Calculate:

density of air = 1.2 kg/m3

If all the air the room was condensed into a liquid it would form a layer about 5mm deep


Measuring Density: Solids

Archimedes287 – 212 BC

Measure the mass Measure the volume

Using a ruler (if regular shape) Using Eureka Jars (by displacement of water) In a measuring cylinder (by displacement of

water) Use ρ = m

V


Measuring Density: Liquids Measure the mass Measure the volume using a measuring cylinder use ρ = m

V


Measuring Density Measure the density of the materials available Don’t forget water Enter your results into a table and calculate the density

Material Mass Volume Density


Aims:• To experimentally find the density of different materials• To calculate the density of different materials

Density recap


Aims:• To describe the molecular structure of solids, liquids

and gases• To explain brownian motion

Brownian Motion 19/04/23

Starter: • draw the structure of a solid, liquid and gas in the

back of your books


Solid• The atoms/molecules vibrate• atoms/molecules cannot move past each other• atoms/molecules are touching

Liquid• The molecules move around

randomly• Molecules are touching

Gas• The molecules move around randomly• There is a lot of space between the particles

Handout

Melt

Boil/ evaporate

sublime

freeze

condense

deposit


If a small visible particle is observed in a fluid it will slowly move without any visible force being applied.

Examples: Smoke particles in air Pollen in water Molecules in the air collide with the smoke

particles randomly and it is moving due to the continually altering resultant force.

Movie Brownian Motion

Brownian Motion

Robert Brown (1773–1858)

Albert Einstein(1879–1955)

First observed in 1785 by Jan Ingenhauz

Demo Brownian Motion Brownian Motion (Video Clip 1

2)


Demo Diffusion Bromine in Air Coloured Water in Gas Jars


Diffusion


Diffusion When particles are released in an enclosed area (i.e. smoke)

they slowly disperse throughout the fluid (i.e. air). This is due to collisions between molecules moving the

particles of the smoke in a random direction.

Movie Diffusion


What is Pressure?


Pressure Definition:

molecules in a gas have a random motion They hit a surface When they hit they exert a force. This force causes the pressure on a surface Can increase the pressure by

more particles (more impacts, therefore more force) Faster particles (harder impacts, therefore more force) Smaller area

Symbol: p Equation: p = F or F = p A

A Mnemonic: Put Foot on Ant or Fluffy Pink Animals Units:

Pascals, Pa N/m2

Note: Pressure is the same at all points in a fluid

F

Ap


Questions1) Calculate the pressure exerted by a 1000N elephant when

standing on the floor if his feet have a total area of 1m2.2) A brick is rested on a surface. The brick has an area of 2cm2.

Its weight is 10N. Calculate the pressure.3) A woman exerts a pressure of 100N/cm2 when standing on

the floor. If her weight is 500N what is the area of the floor she is standing on?

4) Joe sits on a balloon. Joe weighs 500 N and the area of the balloon being sat on is 20 cm2. The balloon will pop if the pressure is greater than 20 N/cm2. Does it pop?

5) Jill weighs 600N, the femur bone in her thigh has an area of 4 cm2. What is the pressure in her thigh bone? She jumps from the first floor window effectively doubling her weight. Her thigh bones can each stand a pressure of 200 N/cm2. Will her bones withstand the impact?

6) Why is a sharp knife easier to use than a blunt knife7) Why would a woman with stilettos damage a floor more than

an elephant would?


Pressure DifferenceDemo: What will happen if the bottle of water is filled with water? Why?

Separate Science


Pressure and Depth• Pressure increases with depth• Pressure is the same in all directions at a certain depth• pressure difference = height × density × g• p = h × ρ × g• So the pressure difference in water (ρ=1000 kg/m3 is a lot

greater than the pressure difference in the atmosphere ρ=1.2kg/m3)

Separate Science


Aims:• To describe the molecular structure of solids, liquids

and gases• To explain brownian motion

Brownian Motion recap


Pressure Temperature and Volume 19/04/23

Aims:• To explain relationships between temperature, volume and

pressure of gasesStarter: Copy and complete the table

Symbol Units Unit Symbol

Temperature T Celsius oC

Temperature T Kelvin K

kilogram

m

A

Volume

Density

newton

p

J


• What happens to the kinetic energy of the particles when a gas is heated?

• What happens to the pressure?

Heating Gases

gas gets hotter

more kinetic energy

more collisions at greater

speed

more pressure


Heating GasesIf a gas is heated:

1. Molecules have more kinetic energy (KE)2. Move faster3. More collisions with the side at greater speed4. More Pressure


What sort of graph would you get if you plotted ‘temperature (TC)’ against ‘the average kinetic energy (KEave) of the particles’.

TC

KEave

Heating Gases

-273

Movie Absolute Zero


If you increase the temperature (in Kelvin) what happens to the kinetic energy?

Tk

KE

Heating Gases


Absolute Zero If a gas is cooled the opposite happens If it is cooled enough the particles stop moving This happens at Absolute Zero (-273 °C) The Kelvin Scale of Temperature starts at absolute zero 1 K ≡ °C

Kelvin Centigrade

- 273

180

273

100

1300

0

-93

0

373

1027

Movie Thermometers


Pressure Law Sometimes called the Gay-

Lussac Law, but normally the pressure law as he has another one named after him.

Gay Lussac published both the pressure and Charles’ Law.

Also established the method of measuring alcohol in drinks (ABV)

Separate Science


Pressure Law: Experiment Place a flask of air into a

water bath. Measure the pressure of the

flask using a pressure sensor or Bourdon (pressure) Gauge

Change the temperature of the water bath in 5 K intervals.

Volume constant

Separate Science


•Definition:• For a fixed mass of gas at a constant volume, the pressure is

directly proportional to its absolute temperature•Equation:

• p/T = constant

• p1/T1 = p2/T2

• Where:

•p is pressure in Pa•T is temperature in K

•Notes:• Only works if temperature is in kelvin• Pa ≡ Nm-2

T (K)

p

(Pa)

Pressure Law Separate Science


Worked Examples

• We normally use the pressure law to compare pressures before and after.

• As p/T = Constant thenp/T before = p/T after

• Hence it is often written as:

• p1/T1 = p2/T2

Separate Science


Question• A solid sphere containing helium is at a pressure of 1 x 105 Pa

and is then cooled from 400 K to 300 K. • What is the final pressure?

p1 = 1 x 105 Pa

T1 = 400 K

T2 = 300 K

p1/T1 = p2/T2

1 x 105 = p2

400 300p2 = 1 x 105.300

400= 7.5 x 104 Pa

Separate Science


Questions1. An airplane contains air at 9 x 104 Pa. During flight the

temperature increases from 260 K to 290K. Assuming the volume of air does not alter, what is the change in pressure?

2. A gas cylinder containing explosive hydrogen gas has a pressure of 5 x 106 Pa at a temperature of 300 K. The cylinder can withstand a pressure of 6 x 106 Pa before it bursts, causing a building-flattening explosion. What is the maximum temperature the cylinder can withstand before bursting?

3. High pressure steam is used in a power station. The steam’s initial pressure is 5 x 105 Pa. After going through the turbine its pressure is 1 x 105 Pa. The steam’s final temperature is 150 C. What was its starting temperature assuming the volume of air is constant?

4. A deep sea diver holds her breath as she surfaces. The pressure in her lungs is 4 x 105 Pa 30 m down and the temperature is 35 C. Atmospheric Pressure = 1 x 105 Pa. If she managed to keep the volume of air constant what temperature would the air in her lungs be when she surfaced?

Separate Science


Robert Boyle Studied the cold and air Modern scientist he relied

on experiments to prove his theories

A Chemist and Physicist not an alchemist and a magician

Robert Boyle1627 - 1691


Boyles Law

• A glass tube is filled with oil except for air at the top.

• The pressure of the oil is increased shrinking the air column.

• The gas is left to cool.• The pressure is dropped

in stages and the volume measured once it has cooled down.

• NB Temperature constant


•Definition:•For a fixed mass of gas at a constant temperature, the volume is inversely proportional to the pressure.

•Equation:

• pV = constant

• p1V1 = p2V2

• Where:

•V is volume in m3

•p is pressure in Pa•Notes:

• Mass must be the same (i.e. no particles escape)• T must be constant

Boyle’s Law

p (Pa)

V

(m3)


Questions1. In the upper atmosphere a weather balloon has a volume

of 50 m3. At ground level (1 x 105 Pa pressure) the volume is 20 m3. What is the pressure in the upper atmosphere

2. A child takes a 0.01 m3 balloon from atmospheric pressure 1 x 105 Pa into an airplane containing air at 9 x 104 Pa. Assuming the temperature does not change what is the volume of her balloon?

3. A climber carries a polystyrene flask up a mountain. The volume of the flask is 0.0002 m3 at sea level. The flask increases in size to 0.0003 m3. Assuming the temperature does not change. What is the pressure at the top of the mountain.

4. A diver is 30 m below the surface where the pressure is 4 x 105 Pa. The volume of their lungs is 0.005 m3. What is the volume of air they could breathe out at atmospheric pressure? (assuming the temperature is constant).


Exam Questions


Explain the Following1) How do hot air balloons work?2) How can a small barbeque tank hold enough propane to

cook with all summer long?3) Why do helium balloons float4) What will effect the time it takes to smell the perfume of a

person who walks past you?

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