Pressure is the concentration of a force, or the force per unit area .

What unit is pressure measured in?

Pressure is measured in pascals (Pa) .

Why do tractors have large tyres?

Large tyres spread the weight (force) of the tractor over a large area . This reduces the pressure , which prevents the heavy tractor sinking into the mud.

Why can a nail be hammered into a wall?

A nail has a sharp pointed end with a very small area . This concentrates the force, creating a large pressure over the small area, allowing the nail to be hammered in.

At what angle do forces from fluid pressure act on a surface?

Forces from fluid pressure act at 90 degrees (right angles) to the surface.

The area used in the pressure equation should always be the ______ area of the object.

The area used in the pressure equation should always be the cross-sectional area of the object.

True or False? Spreading a force over a small area results in a small pressure.

False. Spreading a force over a small area results in a large pressure ; spreading a force over a large area results in a small pressure .

Why do high heels produce a higher pressure on the ground than flat shoes?

High heels have a smaller area in contact with the ground, so for the same force, this creates a higher pressure .

Define atmospheric pressure .

Atmospheric pressure is created when air molecules collide with a surface, creating a force per unit area on that surface.

Explain, in terms of air molecules, why atmospheric pressure decreases as altitude increases.

As altitude increases, the air becomes less dense , so there are fewer air molecules (and less weight of air) above a surface. This means fewer molecules collide with the surface, so the pressure decreases .

The Earth's atmosphere is a ______ layer of air relative to the size of the Earth.

The Earth's atmosphere is a thin layer of air relative to the size of the Earth.

How does the pressure at a point in a liquid change with the height of the column of liquid above it?

Pressure increases as the height of the column of liquid above that point increases, because there is more weight of liquid pushing down.

How does the density of a liquid affect the pressure it exerts?

A denser liquid has a greater weight , so it exerts a higher pressure .

A column of water has one hole near the top and one hole near the bottom. Which hole produces the more forceful jet of water, and why?

The hole at the bottom produces the more forceful jet. This is because pressure is highest at the bottom of the column, due to the greater weight of water above it.

The force from the pressure of a liquid is exerted ______ across the whole surface of an object, and in all directions.

The force from the pressure of a liquid is exerted evenly across the whole surface of an object, and in all directions.

True or False? The pressure of a liquid only acts downwards on a submerged object.

False. The force from a liquid's pressure is exerted evenly across the whole surface of an object, in all directions , not just downwards.

Upthrust is a force that pushes upwards on an object submerged in a fluid (a liquid or a gas), acting in the opposite direction to the object's weight.

What two factors determine the size of the upthrust on a submerged object?

The density of the fluid, and the volume of fluid displaced (which is equal to the volume of the object).

Why does a submerged object experience an upthrust?

There is a difference in pressure between the top and bottom of the object; the pressure is greater on the bottom surface than the top (since pressure increases with depth), creating a resultant upward force .

Why do objects appear to weigh less when immersed in a liquid?

Because of upthrust , an upward force that acts against the object's weight.

An object will float if the upthrust acting on it is ______ to or greater than its weight.

An object will float if the upthrust acting on it is equal to or greater than its weight.

Why will an iron block sink in water?

Iron has a much higher density than water, so it cannot displace enough water to create an upthrust large enough to support its weight.

True or False? A wooden block will sink in water because it is denser than water.

False. A wooden block is slightly less dense than water, so it floats , though it remains partially submerged.

GCSEPhysicsAQAFlashcardsForcesPressure & Pressure Differences in Fluids

Pressure & Pressure Differences in Fluids (AQA GCSE Physics): Flashcards

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Cards in this collection (25)

Define pressure.
Pressure is the concentration of a force, or the force per unit area.
What unit is pressure measured in?
Pressure is measured in pascals (Pa).
Why do tractors have large tyres?
Large tyres spread the weight (force) of the tractor over a large area. This reduces the pressure, which prevents the heavy tractor sinking into the mud.
Why can a nail be hammered into a wall?
A nail has a sharp pointed end with a very small area. This concentrates the force, creating a large pressure over the small area, allowing the nail to be hammered in.
At what angle do forces from fluid pressure act on a surface?
Forces from fluid pressure act at 90 degrees (right angles) to the surface.
The area used in the pressure equation should always be the ______ area of the object.
The area used in the pressure equation should always be the cross-sectional area of the object.
True or False?
Spreading a force over a small area results in a small pressure.
False.
Spreading a force over a small area results in a large pressure; spreading a force over a large area results in a small pressure.
Why do high heels produce a higher pressure on the ground than flat shoes?
High heels have a smaller area in contact with the ground, so for the same force, this creates a higher pressure.
Define atmospheric pressure.
Atmospheric pressure is created when air molecules collide with a surface, creating a force per unit area on that surface.
Explain, in terms of air molecules, why atmospheric pressure decreases as altitude increases.
As altitude increases, the air becomes less dense, so there are fewer air molecules (and less weight of air) above a surface. This means fewer molecules collide with the surface, so the pressure decreases.
The Earth's atmosphere is a ______ layer of air relative to the size of the Earth.
The Earth's atmosphere is a thin layer of air relative to the size of the Earth.
How does the pressure at a point in a liquid change with the height of the column of liquid above it?
Pressure increases as the height of the column of liquid above that point increases, because there is more weight of liquid pushing down.
How does the density of a liquid affect the pressure it exerts?
A denser liquid has a greater weight, so it exerts a higher pressure.
A column of water has one hole near the top and one hole near the bottom. Which hole produces the more forceful jet of water, and why?
The hole at the bottom produces the more forceful jet. This is because pressure is highest at the bottom of the column, due to the greater weight of water above it.
What equation is used to calculate the pressure due to a column of liquid?
$p = h ρ g$
Where p = pressure (Pa), h = height of the column (m), ρ = density of the liquid (kg/m³), g = gravitational field strength (N/kg).
The force from the pressure of a liquid is exerted ______ across the whole surface of an object, and in all directions.
The force from the pressure of a liquid is exerted evenly across the whole surface of an object, and in all directions.
True or False?
The pressure of a liquid only acts downwards on a submerged object.
False.
The force from a liquid's pressure is exerted evenly across the whole surface of an object, in all directions, not just downwards.
Calculate the depth of water in a swimming pool that exerts a pressure of 20 kPa. (density of water = 1000 kg/m³, g = 9.8 N/kg)
$h = \frac{p}{ρ g} = \frac{20000}{1000 \times 9.8}$
h = 2.04 m (3 s.f)
Define upthrust.
Upthrust is a force that pushes upwards on an object submerged in a fluid (a liquid or a gas), acting in the opposite direction to the object's weight.
What two factors determine the size of the upthrust on a submerged object?
The density of the fluid, and the volume of fluid displaced (which is equal to the volume of the object).
Why does a submerged object experience an upthrust?
There is a difference in pressure between the top and bottom of the object; the pressure is greater on the bottom surface than the top (since pressure increases with depth), creating a resultant upward force.
Why do objects appear to weigh less when immersed in a liquid?
Because of upthrust, an upward force that acts against the object's weight.
An object will float if the upthrust acting on it is ______ to or greater than its weight.
An object will float if the upthrust acting on it is equal to or greater than its weight.
Why will an iron block sink in water?
Iron has a much higher density than water, so it cannot displace enough water to create an upthrust large enough to support its weight.
True or False?
A wooden block will sink in water because it is denser than water.
False.
A wooden block is slightly less dense than water, so it floats, though it remains partially submerged.

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