The document discusses pressure, including how it is calculated by dividing force by area. A small area results in high pressure while a large area reduces pressure. This is illustrated using examples of stiletto heels concentrating force over a small area versus boots spreading force over a larger area. Other examples show how caterpillar tracks, snowboards, and snowshoes use a large area to reduce pressure. Liquids exert pressure equally in all directions, with pressure increasing at deeper depths due to the weight of liquid above. The document also discusses how scuba divers must slowly decrease pressure or risk getting "the bends" as nitrogen leaves the blood too quickly.

1. Pressure

2. What do we already know about
pressure?
• Pressure is a force which acts at right angles on
an object
• Pressure is exerted downwards by a solid object
• If the area a force acts on is small, a greater
pressure will be given
• If the same force was applied to a larger area
the pressure will be reduced.
• Gases and liquids exert pressure in all
directions

3. How do we calculate pressure?
• Pressure can be calculated by dividing the force by
the area
• Pressure is measured in Pascals (Pa)
• We sometimes see pressure being measured in
N/m2
or N/cm2
• 1Pa is the same as 1N/m2
Pressure = force
area

4. Sensible shoes?
• The force of our body
pushing down will exert a
pressure
• The surface area of our
shoes in contact with the
ground will affect the
pressure
• These stiletto shoes will
concentrate the force over
a small area
• These shoes will give a
larger pressure and would
not be suitable for walking
on soft ground

5. More sensible shoes
• These boots have a large
surface area
• The weight of a person is
spread out over the larger
surface
• The pressure exerted by the
person is smaller than if they
were wearing stiletto shoes
• A small pressure means you
will not sink into soft ground

6. Examples of where a large area
is needed to reduce pressure.
Caterpillar tracks on diggers and on
tanks
Tyres on a tractor
Skis and snowboards
snowshoes

7. Examples of where a small area is
needed to increase the pressure
• Nails
• Needles
• Kitchen knives
• Scissors
• Drawing pins
• Spade

8. Questions on pressure
1) What combination of
force and area give a
high pressure?
2) What combination of
force and area give a
low pressure?
3) What is the formula for
calculating pressure?
4) What units are pressure
given in?
Answers:
1) Large force and
small area
2) Small force on large
area
3) Pressure = force /area
4) Pascals (Pa)

9. Practice using the formula for
pressure
1. A box weighs 500N. It’s base has
an area of 5 m2
. What pressure
does it exert?
2. Another identical box is placed on
top of the first box. What is the
pressure now?
3. A snowboarder weighs 600N. The
area of the snowboard is 0.5m2
.
What is the pressure on the snow?
Answers:
1. 100 Pa
2. 200 Pa
3. 120 Pa

10. Liquid pressure
• Liquids are made up of particles
• The particles can move in all
directions
• The pressure exerted by a liquid
acts in all directions too
• Liquids with a high density will
exert a higher pressure
• As you go deeper, the pressure
increases
• This is due to the weight of all the

11. Water pressure and body
pressure
• Water pressure
acts in all
directions on this
fish
• The fish’s body
pushes back with
an equal and
opposite pressure

12. List the fish under the highest
pressure to the lowest pressure
• Flipper
• Bubbles
• Snapper
• Angel
Angel
Snapper
Bubbles
Flipper

13. Water pressure and scuba
divingWhen this deep sea diver goes
deeper, the water pressure on
his body increases. This will
cause
his blood pressure to increase.
The
increased pressure inside his
body
causes gas exchange in his
lungs to
happen at a greater rate. It
also

14. Problems for scuba divers
• As a diver ascends the water
pressure will decrease, and the
diver’s blood pressure will
decrease.
• The nitrogen which dissolved in
the blood easily under high
pressure will come back out.
• If the diver decompresses too
quickly the nitrogen leaves the
blood so quickly it will bubble
and fizz like carbon dioxide from
a bottle of pop.
• This is known as the ‘bends’.

15. A cure for the bends
• A diver can go into a decompression
chamber to avoid getting the ‘bends’
• The pressure in the chamber is
controlled to change slowly from high
pressure to a low pressure.
• This allows the diver’s pressure to
decrease slowly to avoid nitrogen
leaving the blood so quickly.