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Help with Pressure




Try some Calculations

Plug in these examples:
the force is the weight of the block placed on a table: 80 N
The area of the force is the base area of the block: 2 square metres

What is the pressure on the table?

Fun Fact:
Camels need to be able to walk around on sand without sinking into it.
This means that they need to reduce their pressure on the ground.
Large feet mean a large area of contact, and thus less pressure.

The Pressure of air is known as
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Air Pressure on Flame




Air Pressure in Straw
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We don't feel the air pressure because our body fluids push back!

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Example: Your ears popping in an airplane
What causes your ears to pop?



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When volume decreases, pressure increases

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When temperature increases, pressure increases
(though volume does not increase)


The opposite is true, too. When temperature decreases, pressure decreases
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Water pressure also increases the deeper you go under water.

The pressure pushing up on an object is stronger than the pressure pushing down.
This is because the bottom of the object is deeper than the top of the object.

The upward force is called the
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The idea of buoyancy was summed up by Archimedes, a Greek mathematician,
in what is known as Archimedes Principle:
Any object, wholly or partly immersed in a fluid,
is buoyed up by a force equal to the weight of the fluid displaced by the object.
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Use the information below to answer the following questions:
What is the density of each object?
If all are put in a container, which will float on top, which will be in the middle, and which will sink?
Liquid A: Mass=40g and Volume=10mL
Liquid B: Mass=25g and Volume=10mL
Object C: Mass=18g and Volume=6mL



What happens when you squeeze a plastic bottle filled with water?
If closed, the water has no where to go and the pressure is the same all in the bottle
not just where you squeezed it. This is known as Pascal's Principle.
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Questions to check your understanding

1. What is the pressure on 2 square meter surface where you push with a force of 6 Newtons?

2. What pressure is created when 5.0 N of force are applied to an area of 2 square meters?

3. How does the pressure change if the force is increased to 10.0 N? (from ques. 2)

4. A sample of 10.00g of oxygen has a volume of 6702 mL. The sample weight of carbon dioxide is the same as that of the oxygen but it occupies 5058 mL. What is the density of each gas?

5. The density of methanol at 20oC is 0.791g/mL. What is the mass, in g, of a 280 mL sample?