1. Pressure in Solids

2. Which is the odd one out?
Why?

3. Bed of nails

5. Area Bigger Force Smaller
Pressure
force
Pressure is the amount of …………… pushing on a certain ……………
The bigger the force the …………… the pressure
The bigger the area the …..………… the pressure
area
bigger
smaller
Key words
Area Bigger Force Smaller

6. In your books
Aim
To investigate the effect of surface area on the size
of impact with a constant force
Diagram of set up
Results & Conclusion
And an explantion/ conclusion/ how
Surface in contact
Size of crater
Explanation
At least 6 different ex.

7. Spreading the Load
Answer the question below in a full sentence in your book
Why has Eskimo Fran fallen through the ice when Eskimo Percy hasn’t?
Answer: Eskimo Percys weight is spread out over a bigger surface area because of his snow shoes!

9. Pressure is measured in Newton’s per square metre (N/m2) This is also called a Pascal (Pa)
1 Pa = 1 N/m2
The area of Fran’s shoes is 150cm2, He weighs 600N
The area of Percy’s snow shoes is 360cm2, He weighs 750N
Work out how much pressure is put on to the snow by their shoes
Pressure = force ÷ area
Fran = 600N ÷ 150cm Percy = 720N ÷ 360cm2
= 4N/cm2 = 2N/cm2

10. Pressure in liquids

11. Liquids cannot be compressed because the particles are already close together11

12. This means that liquids can be used to send forces from one place to another in hydraulic systems
Liquids cannot be compressed because the particles are already close together 12

13. YouTube - ridiculous hydraulicsX
YouTube - ridiculous hydraulics 13

14. Piston X puts pressure on the liquid
Force = 20N
Force = 10N
Piston X puts pressure on the liquid Y X
Area = 10cm2
Area = 40cm2
How do we calculate the pressure that is being applied from piston X? 14

15. f p a force area Force = 20N Force = 10N Y Area = 10cm2 pressure =X
Ask pupils to calculate the pressure from piston x. Demonstrate how to calculate the force by rearranging the equation (higher pupils will probably only understand this point)
Area = 10cm2
pressure =
force
Area = 40cm2
area 15

16. What would the pressure be at piston Y?
Force = 20N
Force = 10N
The pressure stays the same throughout the liquid Y X
The same as piston X = 1N/cm2
Area = 10cm2
Area = 40cm2
What would the pressure be at piston Y? 16

17. Force
Area
b) Force =
Pressure  Area
a) Pressure =
= 5N/cm2 x 20cm2
10N
2cm2
= 100N
= 5N/cm2

18. Pressure in Liquids In a liquid: Pressure acts in all directions and
pressure increases with depth.

19. Pressure (N/m2) = 10 N/Kg x depth (m) x density (Kg/m3)
The relationship between pressure and depth is shown by a water bottle with holes along its length.
low pressure
High pressure
Pressure (N/m2) = 10 N/Kg x depth (m) x density (Kg/m3)
The deeper you go, the higher the pressure
The denser the liquid, the heavier it is!
The pull of gravity

20. Force
Area
b) Force = Pressure  Area
= 3N/cm2  30 cm2
Force = 90 N
a) Pressure =
Pressure = 30 10
Pressure = 3N/cm2 or Pascals (Pa)

21. Force
Area
b) Force =
Pressure  Area
a) Pressure =
= 1N/cm2 x 100cm2
10N
10cm2
= 100N
= 1N/cm2

22. Force
Area
a) Pressure =
b) Force =
Pressure x Area
= 10N/cm2 x 200cm2
20N
2cm2
= 10N/cm2
= 2000N

23. Air Pressure

24. To begin with ... Explaining why
Can you pull the Madeburg hemispheres apart?
Why is this happening? 24

25. Atmospheric pressure us about 100 000Pa
(although it changes day to day)
That like having one kilogram resting on every square centimetre of your skin!
The fluids inside your body are of a similar pressure so it evens out
How come you don't notice this pressure? 25

26. A vacuum is a space where there are no particles at all
The pressure outside the hemispheres is greater than the inside
This pushes them together 26

27. Manometer
We can measure the air pressure
using a manometer

28. Manometer
When the pressure acting on the left equals the pressure on the right the height either side of the manometer is the same

29. Manometer
The pressure on the left (the air pressure) is the same as before
BUT the pressure on the right is now bigger (different gas)
So for it to be even…
The air pressure AND the pressure caused by the difference in height from the liquid can then balance.
And luckily…
we have an equation for that
BRILLIANT
+ =

30. Pressure = g ρ h REALLY IMPORTANT
The manometer measures the difference in the pressure between two gasses
Therefore if you want the actual pressure of the gas you need to add that on to what you have found using the equation

31. Barometer The barometer works in a slightly different way.
This has a vacuum at the top, so rather than comparing two different gases it gives you the pressure of the gas acting on the surface- this is difficult to use with anything other than air pressure

32. Mercury Barometer
When we use a Mercury barometer (Very heavy liquid) we can use a different unit of measurement.
mmHg
Millimetres of mercury
… Is just that, can just measure the difference in height in mm
Atmospheric pressure is 760mmHg

33. Pressure