Pressure
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Electricity
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Forces and motion
Energy
Earth and atmosphere
Acids and alkalis
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Pure and impure substances
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Explainer Video
Summary
Pressure
In a nutshell
Pressure is defined to be the force per unit area. This means that it depends on the size of the force being applied and the area of the surface that the force is being applied to.
Equations
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Variable definitions
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Pressure calculations
A fluid is either a gas or a liquid. Pressure acts in a fluid in all directions. You can calculate the pressure on the surface of a fluid if you know the force being exerted onto the fluid and the area over which the force is being exerted.
Pressure is measured in pascals, . The pascal can also be written as as forces are measured in newtons and area in metres squared.
Atmospheric pressure
The atmosphere is the thin layer of air that surrounds the Earth, it contains a mixture of gases and the particles of these gases collide with objects as they travel through the atmosphere.
The atmospheric pressure decreases as the height above the surface of the Earth increases, this is because the weight of the air above you is lower.
Pressure in a liquid
For an object submerged in a liquid, the pressure on the object depends on the depth of the object in the liquid. The pressure in a liquid increases as the depth increases, this is because the weight of the liquid above is greater.
Upthrust
When an object floats in a fluid, there is an upward force acting on it called the upthrust force and this force allows objects to float.
Example
If a box is floating on water, it has its weight acting on it and an upthrust force also acting on it. The upthrust keeps the box from sinking by acting in the opposite direction to gravity.
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FAQs - Frequently Asked Questions
What is a fluid?
A fluid is either a gas or a liquid.
What is density?
The density lets you know how close together the particles of the object are.
What is pressure?
Pressure is defined to be the force per unit area.