CARSAnd Forces - Pressure

PressurePressure

To be able to:

All Most Some

Say what is meant by pressure

(MYP 2/3)

Calculate pressure

(MYP 3/4)

Explain how forces can be spread out or concentrated on a small area

(MYP 5/6)

Starter – What is pressure?

If forces balance, do they cancel each

other out?

Pressure is exerted whenever a force is applied over an area.

If the same force is applied in each picture, which arm exerts the highest pressure on the

board?

1. 2.

What is What is pressure?pressure?

The arm applies a force to the board via a

fingertip.

The force acts over a small area and so

produces a high pressure.

1.

High and Low PressureHigh and Low Pressure

The same force is now acting over a larger area –

the palm has a greater surface area

than the fingertip. A lower pressure is produced.

2.

PressurePressureExplain how the following work:

1) A sharp knife is easier to use then a blunt knife.

2) A drawing pin.

3) A woman with stilettos on might damage a floor more than an elephant would.

Pressure depends on ______ and ______

PressurePressurePressure depends on two things:

1) How much forceforce is applied, and

1) How big (or small) the area area on which this force is applied.

Pressure is measured in:newtons per square metre (N/m2),

Pressure can also be measured in:newtons per square millimetre (N/mm2);newtons per square centimetre (N/cm2).

pressure =area

force

p x a

f

Pressure is the force per unit area and is calculated using this formula:

Calculating pressureCalculating pressure

Pressure calculationsPressure calculationsMr Bobdy Bilda has a block

1. What is the pressure of Bobdy’s block on the ground?•The force is the weight = 60N•Area on the ground = 2m x 1m

= 2m2

•So the pressure of the block is 60/2 = 30N/m2

•What if Bobdy turned the block on its side?

Weight 60N

2m

1m

3m

Pressure QuestionsPressure 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 20cm2. 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) The area of contact of four car tyres with the road is 300 cm2. The pressure exerted is 50 N/cm2. Work out the weight of the car.

1000 N/m2

0.5 N/cm2

5 cm

15,000 N

How do skates work?How do skates work?

PlenaryPlenary

Prepare a short live presentation to explain to Year 3 children how skates and skis work.

HomeworkHomework

Update the mind map you made earlier.

Add topics and keywords that we have used recently.

Stick it in your book

PressurePressureTo be able to:

All Most Some

Say what is meant by pressure

(MYP 2/3)

Calculate pressure

(MYP 3/4)

Explain how forces can be spread out or concentrated on a small area

(MYP 5/6)

If forces balance, do they cancel each

other out?

In a short sentence, explain how FORCE and PRESSURE are:

(a)(a) SimilarSimilar(b)(b) DifferentDifferent

Pressure - revisitedPressure - revisited

To be able to:

All Most Some

State how to calculate pressure(Level 4)

Calculate pressure in different situations(Level 5)

Design an experiment to calculate large and small pressures (Level 7)

Starter – what are the important ideas about Pressure Agree on your table ... Ask others if you need to

Is a drawing pin well designed?

Why would a lady in high heels standing on your foot hurt more than an elephant standing on your foot?

Under PressureUnder Pressure

high pressuremedium pressure

Possible DemonstrationPossible DemonstrationDemonstrate air pressure with 30cm ruler

Balance over end of desk and strike overhang with, successively

• Sheet of newspaper screwed up tightly.• Sheet of newspaper carefully folded into 8.• Sheet of newspaper spread out carefully.

• What causes what you see.

Safety: watch where you are propelling the ruler and missile

high pressure

low pressurePressure in a liquid acts in all directions and increases with

depth.

Pressure in Liquids and GasesPressure in Liquids and GasesLiquids

GasesThe particles move in all directions and push

on their container (“pneumatic”)

http://www.animatedengines.com/otto.html

Practical Practical

• Work in groups of 4• What is the greatest pressure you can put on the

floor of the room?• ... And the smallest

• Equipment: Newton scales, graph paper, mural paper

• You should be prepared to estimate!

Pressure - revisitedPressure - revisited

To be able to:

All Most Some

State how to calculate pressure

(MYP 1/2)

Calculate pressure in different situations

(MYP 3/4)

Design an experiment to calculate large and small pressures

(MYP 5/6))

Starter – what are the important ideas about Pressure Agree on your table ... Ask others if you need to

Is a drawing pin well designed?

Review

How does depth affect water How does depth affect water pressure?pressure?

Look at the graph below showing the changes in water pressure with depth:

a) Describe the pattern shown in the graph.

As the depth increases the water pressure increases.

b) Predict what would happen to the size of an inflated balloon if it was carried down beneath the surface of the water by a diver.

The inflated balloon would decrease in size the deeper it went.

c) Explain your reasons for your prediction in part ‘b’.

The increasing water pressure would exert a force on the sides of the balloon, compressing the gas

contained inside.

PlenaryPlenary: Pressure – highest to lowest: Pressure – highest to lowestThe woman weighs 400N Each stiletto heel has an area of 1cm2

The elephant weighs 4000N. Each foot has an area of 100cm2

Atmospheric Atmospheric PressurePressureTo be able to:

All Most Some

Describe how the atmosphere pushes down on us

(MYP 1/2)

Explain how atmospheric pressure makes some things happen

(MYP 3/4)

Explain atmospheric pressure using particle theory

(MYP 5/6)

Starter – An egg has a diameter of 4cm. How could you get it into a flask with an

opening 3.5 cm wide?

Do we live under a sea of air?

Egg in a bottle demonstrationEgg in a bottle demonstration• Show a wide mouthed conical flask and an egg• Challenge one of the pupils to try and push the egg into

the flask intact – it will get messy! • Put a little water in the flask and place a hard boiled

shelled egg on the mouth. Heat the water using a Bunsen, switch off when the water is boiling and the egg starts to wobble. The egg should slowly be sucked in intact.

• What is happening?• Discuss the pressure of the atmosphere and why we don’t

feel it.• (video on next slide in case it doesn’t work!)

Air PressureAir Pressure• How did the egg get into the bottle?

• Why does the plastic bottle collapse?

• Why does a helium balloon float? (After all it weighs something!)

egg in a bottle video

gas pressure in a bottle

Numbered heads togetherNumbered heads together• Listen to the question and the

time you have to solve it• Teacher then says “Butts up”.• Stand up and lean into the centre

of the table to decide on the answer.

• When you all know the answer, sit down.

• The teacher picks a number.• That pupil from each team writes

the answer on a whiteboard and stands up. This must be done in silence.

• The teacher gives a signal and each team shows the answer at the same time.

Pressure ChallengePressure Challenge• 1. Why did the egg go into the bottle?

• 2. Why did the bottle collapse?• 3. Why do you feel pressure on your eardrums in the deep end of the pool?

•  4. Why does water boil at around 70ºC up Mount Everest?

•  5. Why can divers only go so far without a submersible?

Diagram and 5 key words

Atmospheric Atmospheric PressurePressureTo be able to:

All Most Some

Describe how the atmosphere pushes down on us(MYP 1/2)

Explain how atmospheric pressure makes some things happen(MYP 3/4)

Explain atmospheric pressure using particle theory(MYP 5/6)

Starter – An egg has a diameter of 4cm. How could you get it into a flask with an

opening 3.5 cm wide?

Do we live under a sea of air?

PlenaryPlenaryDraw a concept map linking at least the following

words and units

Force

Pivot

Pneumatic

Hydraulic

Pressure

MomentCounter balance

Balance

Turning effect

Weight

FrictionLever

KgN/cm2

N/m2

N

Nm

Atmospheric

HomeworkHomework

Get another picture of your car…Draw accurate force diagrams on it…

Now research how your car is designed to use or overcome the forces acting upon it!