1. Pressure

2. Lesson 1

3. Fluids Demonstration
What happened to the shape of the water as it was moved to different containers?
Is a liquid the only substance that can take the shape of its container?
In your groups discuss what else behaves in this way.
Do these substance apply any force?

4. Both Liquids and Gases are Fluids
Any substance that can flow and take the shape of the container that holds it
Both Liquids and Gases are Fluids

5. Pressure of Fluids 1
All fluids apply something we call pressure and is related to weight 2
Does air have weight? Let’s find out!

6. Balloon Demonstration
What is happening to the meter stick as the air is let out of the balloon?
Why is this happening?
Will the same happen if the balloons were filled with water?

7. What is Air Pressure?
It is caused by the weight of all the air in the atmosphere pressing down on Earth
Air pressure is greater near the ground than it is higher in the sky.
Why is that?
Hint: Think back to our weather unit

8. Air Pressure Imagine a pile of books stacked one on top of the other.
The weight or pressure on the bottom book would be much greater than the pressure on the top one.
It’s the same with air molecules; those molecules on the bottom have greater pressure on them than those above.

9. Definition of Atmospheric Pressure
The ratio of the weight of all the air above you to your surface area is atmospheric pressure

10. Definition of Underwater Pressure
It is a combination of the weight of the water on top of the object and the weight of the air on top of the water.
As the object moves deeper underwater
the amount of water increases above it
(Figure 4 pg. 898)

11. The deeper the water the greater the pressure because the weight of the water is greater near the bottom.

12. Lesson 2

13. Lesson Objectives
How do force and area affect pressure?

14. How do we calculate Pressure?
Pressure is the FORCE over a given AREA
Pressure is measured in Pascals (Pa)

15. Force and Area
Pressure decreases when the area over which a force is applied increases

16. High pressure and low pressure
The shoes have flat soles, so they spread the person’s weight over a large surface area.
These boots exert a low pressure on the ground.
In contrast, the soles of the high-heeled boots have a smaller surface area and so exert a higher pressure.
These shoes are likely to sink into soft ground.
Photo credit: © 2008 Jupiterimages Corporation

17. Which of these objects rely on low pressure, and which on high pressure? How do they achieve this?
Snow shoes
Hypodermic syringe
Sharp knife
Camel’s feet
Comfy chair

18. Calculating pressure f p a force pressure = area
Pressure is the force per unit area and is calculated using this formula: f p a
pressure =
area
force
This can also be represented in a formula triangle.
Pressure is measured in newtons per square metre (N/m2), which are also called pascals (Pa).

19. Pressure Calculations
A force of 20 N acts over an area of 4 m2.
Calculate the pressure.
Pressure = Force ÷ Area
20 N ÷ 4 m2 = 5 N/m2
Sometimes you will see another unit being used. This is called the pascal and it has the symbol Pa.

20. Pressure Calculations
A hammer supplies a force of 700 N. The hammer head has an area of 7.1 x 10-4 m2. What is the pressure?
P = F/A
P = (700 N/7.1 x 10-4 m2)
P = x 105 N/m2
P = x 105 Pa

21. Applying Pressure Calculations
Ice Road Truckers Activity

22. Teacher Instructions
Watch the opening two minutes of to set the scene.
Print and distribute slides
Groups will swap posters and evaluate the other group on whether they did the calculations correctly and if they got the correct answer

23. Objective: To calculate pressure and apply to a real life situation.

24. A dangerous Job

25. But Science and Math help to make it possible!

26. How would you work out how much pressure is being put on the ice?

28. The trucks tyres have an area 1000cm2 in contact with the ice
Its weight (the force) is N.
Pressure = Force / Area
/ 1000 = 400 N/cm2
The ice road can withstand pressure of up to 500N/cm2.

29. The ice road can withstand pressure of up to 500N/cm2.
So the truck will not break ice!

30. Group task You are the latest recruit for the ice road truckers.
You must select a vehicle that will drive on the ice roads.
It must not fall through the ice!

31. How to achieve in this task
Work out the amount of pressure that each truck puts on the ice.
Select which truck will be able to do the job.
Present your findings in the form of a poster.

32. The ice road can withstand pressure of up to 500N/cm2.
Which trucks will break the ice? Which truck will be suitable?

33. Truck Name: Do not say Snow to me
Truck Name: Do not say Snow to me! Weight: 500,000 N Area of Tyres: 800cm2

34. Truck Name: Ice Ice Baby Weight: 400,000 N Area of Tyres: 500cm2

35. Truck Name: It’s Snow Joke Weight: 600,000 N Area of Tyres: 1000cm2

36. Truck Name: Ice to Meet You Weight: 400,000 N Area of Tyres: 900cm2

37. Peer Marking
Swap posters with another group. Award it a level based on the outcomes of the lesson.
Recall the equation for calculating pressure (level 4)
Use the equation to calculate pressure (level 5)
Provide scientific evidence to back up a decision made (level 6)

38. Plenary: Hold up the correct card
What is the equation for pressure?
(a) Pressure = force/mass
(b) Pressure = area/force
(c) Pressure = force/area
(d) Pressure = mass/area

39. Plenary: Hold up the correct card
An elephants weight is 12000N and the area of its feet is 400cm2 .How much pressure does the elephant exert on the ground?
(a) 1000N/cm2
(b) 8000N/cm2
(c) N/cm2
(d) 30N/cm2