1. Pressure

2. How does this work?

3. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
The pressure of a gas in a sealed container is caused by the collisions of with the container wall.
An increase in the temperature of the gas increases the pressure because the of the increases.
The force on the wall due to the gas is the pressure multiplied by the of the wall.

4. Learning Objectives By the end of this lesson you should be able to...
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.

5. Calculating pressure force pressure = area
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Calculating pressure
Pressure is the force per unit area and is calculated using this formula:
pressure =
area
force
Pressure is measured in: newtons per square metre (N/m2), which are also called pascals (Pa).
Pressure can also be measured in: newtons per square millimetre (N/mm2); newtons per square centimetre (N/cm2).

6. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Imploding Bottles
Atmospheric pressure is equal to 100,000 Pa or 100 Kpa. As this pressure is present both above and below objects in the lower atmosphere the forces are in equilibrium therefore no resultant force is exerted. So… how could I do this?

7. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Imploding Bottles
When you seal a bottle the pressure inside and outside are in _________.
If pressurised at high altitude the pressure inside the bottle will be _______ than if it had been pressurised at sea level.
When the bottle is taken ______ the mountain / hill it will gradually compress as the pressure on the outside is ________ than the pressure inside.

8. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
World’s Longest Straw
Veritasium
When drinking through a straw you expand your lungs to reduce the air pressure inside the straw. As a result atmospheric pressure pushes the liquid up the straw.
Is there a limit to the length of the straw that this would work for?

9. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Which type of pressure?
Which of these exerts a higher pressure on the ground – explain your answer.
Which of these would you use to cross a muddy field?

10. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Using low pressure
A force spread over a large area means low pressure, e.g. skis and snowboards.
The large surface area of the board means the skier exerts very little pressure on the snow.
This means he slides over the top of the snow and does not sink into it.

11. Pressure in a liquid The greater the depth, the higher The pull
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Pressure in a liquid
Much like atmospheric pressure, the relationship between pressure and depth in a liquid is shown by a water bottle with holes along its length.
Pressure (N/m2) = 10 N/kg x depth (m) x density (kg/m3)
The pull
of gravity
The greater the depth, the higher
the pressure
The denser the liquid, the heavier it is

12. Calculate the Pressure when…
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Calculate the Pressure when…
A diver is 12m beneath sea level, assuming that water has a density of 1000kg/m3
How much greater would the pressure be if he had dived in syrup, with a density of 1330kg/m3
A submarine is 1.3km beneath sea level, assuming that water has a density of 1000kg/m3
EXT1: How deep would a diver be beneath the water if the pressure were 240,000 Pa.
EXT2: Sea waters actual density is 1027kg/m3 because of the additional salt. Recalculate Q1 and 3 with this new value.
Pressure (N/m2) = H x ρ x g

13. Hydraulics
Hydraulic systems use the principle that pressure is transmitted throughout a liquid to allow a force applied in one part of a system to be transferred to another.
This allows us to avoid linking the parts mechanically. All hydraulic systems use two pistons linked via a pipe carrying a special oil called hydraulic fluid.
Force
applied
here
Force
transferred
here
Pressure inside all parts of the
hydraulic system is the same

14. Hydraulic brake hydraulic fluid slave pistons foot pedal master piston
All hydraulic brake systems (e.g. in a car) use a small master piston and a bigger slave piston.
hydraulic fluid
slave pistons
foot pedal
master piston
The master piston is used to apply a force. This puts the liquid under pressure. The pressure is transmitted to the pistons on all four wheels of the car.

15. Hydraulic Brake

16. Hydraulics activity

17. Barometer Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Barometer

18. Barometer Using the key words explain how a barometer works:
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Barometer
Using the key words explain how a barometer works:
Atmospheric Pressure
Mercury
Sealed End
Rises / Falls
Force
Scale
Higher / Lower

19. Manometer Listen to the explanation – describe how it works.
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Manometer
Listen to the explanation – describe how it works.

20. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Manometer
Under normal atmospheric conditions liquid in a tube will settle to the same level either side as the pressure exerted on either side is equal.
This fact can be exploited for use in a manometer, which uses the difference in height to deduce the additional pressure on one side. Used widely in the gas industry.

21. For you to try…. Read page P68 Try the questions on P69.
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
For you to try….
Read page P68
Try the questions on P69.

22. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
How does this work?
Boyle’s Law
Average energy of particles determines the temperature of the substance.
Warmer substances have particles which are vibrating more ________. They are therefore _________ with each other, and the walls, of the container more __________. This is felt as increased _________.
Increasing temperature and keeping a fixed volume will always result in greater _________.

23. Boyle’s Law But … what about if temperature is kept constant.
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Boyle’s Law
But … what about if temperature is kept constant.
The pressure on the walls of the container is now a result of the volume. _______ volume will mean fewer collisions with the walls therefore ________ pressure.
Pack the same number of particles into a small space, _______ volume, and they collide ______ frequently with the walls therefore producing a higher temperature.

24. P1V1 = P2V2 Boyle’s Law P = Pressure of gas / N/m2 or Pa
Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
Boyle’s Law
P1V1 = P2V2
P = Pressure of gas / N/m2 or Pa
V = Volume of gas / m3

25. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
P1V1 = P2V2
If we compress a gas then we lower the volume but the pressure increases.
If we allow the gas to fill a larger container then we increase volume but decrease the pressure.
P X V = Constant

26. Learning Objectives
By the end of this lesson you should…
Recall the formula for pressure as a function of force and area.
Explain how pressure on a solid and in a liquid can be determined mathematically.
Explain hydraulic pressure and explain some simple machines which use the principles.
State Boyles law and explain the effect of temperature and volume on the pressure of a gas.
P1V1 = P2V2
P and V are inversely proportional – i.e. when one increases the other must decrease.
P and 1/V are directly proportional – i.e. both increase at a constant rate.