Pressure

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Lesson notes

What is Pressure?

**Pressure** is a measure of how much **force** is applied over a given **area**.
The same force applied over a smaller area produces a larger pressure.
Pressure in a liquid increases with depth because of the **weight of liquid above**.
Atmospheric pressure decreases as altitude increases because there is less weight of air above.

Pressure in Liquids

In a bottle of water, pressure is greatest at the **bottom** and least at the **top**.
The hole at the bottom has the most water above it, so water shoots out **fastest**.
The hole at the top has the least water above it, so water comes out **slowest**.
This demonstrates that liquid pressure depends on **depth**.

Atmospheric Pressure

The atmosphere exerts **pressure** on everything due to the weight of air.
Atmospheric pressure **decreases** as you go higher above Earth's surface.
Higher altitude means less air above, so lower pressure.

The Pressure Equation

Pressure = Force ÷ Area
Force is measured in **Newtons (N)**.
Area is measured in **square metres (m²)**.
Pressure is measured in **Pascals (Pa)** or N/m².
1 Pa = 1 N/m².

Example Calculation

A force of 500 N acts on an area of 0.25 m².
Pressure = 500 N ÷ 0.25 m² = **2000 Pa**.
Always write the equation, substitute values, then calculate with units.

Applications of Pressure

A **high heel shoe** has a small area, so it exerts a large pressure and sinks into soft ground.
A **trainer** has a larger area, so it exerts a smaller pressure and sinks less.
Reducing area increases pressure; increasing area reduces pressure.

Particle arrangement in solids, liquids, and gases. Pressure in liquids and gases arises from particle collisions.

Diagram showing three holes in a water bottle at different depths. The bottom hole has the highest water pressure, so water shoots out fastest.

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Practice questions

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1.Which equation correctly links pressure, force, and area?
Easy
- APressure = Force × Area
- BPressure = Force ÷ Area
- CPressure = Area ÷ Force
- DPressure = Force + Area
2.What is the unit of pressure?
Easy
- ANewton (N)
- BMetre squared (m²)
- CPascal (Pa)
- DNewton per metre (N/m)
3.As we go higher above the Earth's surface, atmospheric pressure:
Easy
- Aincreases
- Bdecreases
- Cstays the same
- Dbecomes zero
4.A bottle has three holes at different heights. From which hole does water come out fastest?
Medium
- AThe top hole
- BThe middle hole
- CThe bottom hole
- DAll holes at the same speed
5.A crate weighs 2600 N and has a base area of 2 m². What pressure does it exert on the ground?
Medium
- A1300 Pa
- B5200 Pa
- C130 Pa
- D2600 Pa
6.A book weighing 20 N lies on a table, covering an area of 0.02 m². The pressure exerted by the book on the table is:
Medium
- A1000 Pa
- B100 Pa
- C0.001 Pa
- D400 Pa
7.A skip weighing 5000 N has a base area of 4 m². The pressure on the ground is:
Medium
- A1250 Pa
- B20000 Pa
- C125 Pa
- D5000 Pa
8.A person weighing 700 N stands on the ground. The combined area of their shoes is 0.04 m². The pressure they exert is:
Hard
- A17500 Pa
- B28 Pa
- C1750 Pa
- D28000 Pa

More questions

9.Which shoe is more likely to sink into soft ground?
Hard
- AA trainer, because it has a larger area
- BA high heel, because it has a smaller area
- CBoth sink equally
- DNeither sinks
10.Force is measured in:
Easy
- APascals
- BNewtons
- CMetres squared
- DKilograms
11.If the force on an area is doubled while the area stays the same, the pressure:
Medium
- Ahalves
- Bdoubles
- Cstays the same
- Dquadruples
12.A force of 100 N is applied to an area of 0.5 m². What is the pressure in Pa?
Hard
- A50 Pa
- B200 Pa
- C500 Pa
- D20 Pa
13.A student pushes a drawing pin into a noticeboard. The pin exerts a force of 10 N on the board. The area of the pin's tip is 0.00002 m². What is the pressure exerted by the pin tip on the board?
Easy
- A500,000 Pa
- B0.000002 Pa
- C500 Pa
- D200,000 Pa
14.A box weighing 600 N has a base area of 1.5 m². What pressure does it exert on the floor?
Easy
- A900 Pa
- B400 Pa
- C0.0025 Pa
- D600 Pa
15.A student uses a knife to cut an apple. The blade has a force of 50 N applied over a cutting edge area of 0.0001 m². What is the pressure exerted by the blade?
Medium
- A500,000 Pa
- B50,000 Pa
- C0.005 Pa
- D500 Pa
16.A car tyre exerts a pressure of 200,000 Pa on the road. If the area of contact of the tyre with the road is 0.02 m², what force does the tyre exert?
Medium
- A4,000 N
- B10,000,000 N
- C400 N
- D10,000 N
17.A hydraulic lift uses a small piston of area 0.01 m² and a large piston of area 0.5 m². A force of 100 N is applied to the small piston. What is the force exerted by the large piston? (Assume pressure is transmitted equally throughout the fluid.)
Hard
- A5,000 N
- B2 N
- C500 N
- D50 N
18.The graph shows how pressure varies with depth for a liquid. Which statement is correct?
Medium
- APressure increases linearly with depth.
- BPressure decreases linearly with depth.
- CPressure is constant at all depths.
- DPressure increases with depth but not linearly.
19.A student measures the pressure at the bottom of a swimming pool. Which of the following would increase the pressure at the bottom?
Medium
- AUsing a denser liquid
- BMaking the pool wider
- CMaking the pool narrower
- DRemoving some water from the pool
20.A submarine window has an area of 0.5 m². At a depth where the water pressure is 400,000 Pa, what is the force exerted by the water on the window?
Hard
- A200,000 N
- B800,000 N
- C200 N
- D0.00000125 N
21.In an experiment, a student measures the pressure at different depths in water. The results are shown in the table. What is the pressure at a depth of 3 m?
Hard
- A30,000 Pa
- B20,000 Pa
- C10,000 Pa
- D40,000 Pa
22.A student uses a barometer to measure atmospheric pressure at sea level and on top of a mountain. Which statement is correct?
Easy
- AAtmospheric pressure is lower on the mountain top.
- BAtmospheric pressure is higher on the mountain top.
- CAtmospheric pressure is the same at both locations.
- DAtmospheric pressure is zero on the mountain top.
23.A water tank has a hole at the bottom. The water emerges at a speed of 4 m/s. If the tank is filled to double the height, what happens to the speed of water emerging?
Medium
- AIt becomes greater than 4 m/s.
- BIt becomes less than 4 m/s.
- CIt stays the same.
- DIt becomes zero.
24.A student pushes a block of mass 20 kg onto a surface. The block has a base area of 0.1 m². What is the pressure exerted on the surface? (g = 10 N/kg)
Hard
- A2000 Pa
- B200 Pa
- C20 Pa
- D2 Pa
25.A student investigates how the depth of water in a tank affects the speed of water coming out of a hole at the bottom. Which piece of equipment is needed to measure the speed of the water?
Medium
- AA stopwatch and a measuring cylinder
- BA ruler and a balance
- CA thermometer and a barometer
- DA newton meter and a tape measure
26.A student sets up an experiment to measure the pressure at different depths in a liquid. They use a pressure sensor attached to a rod. Which of the following should they do to ensure accurate results?
Hard
- ALower the sensor slowly and take readings at each depth
- BLower the sensor quickly to avoid disturbing the liquid
- CUse the same depth for all readings
- DHold the sensor at an angle to measure sideways pressure
27.In an experiment, water flows out of a hole at the bottom of a tall cylinder. The height of the water column is 2.0 m. The speed of the water as it leaves the hole is 6.3 m/s. If the height is increased to 4.0 m, what is the new speed? (Assume no energy loss and g = 10 N/kg)
Medium
- A8.9 m/s
- B12.6 m/s
- C6.3 m/s
- D4.5 m/s
28.A student uses a barometer to measure atmospheric pressure at sea level and then on a mountain top. The reading on the mountain top is lower. Which of the following best explains this observation?
Medium
- AThere is less weight of air above the mountain top
- BThe temperature is lower on the mountain top
- CThe mountain is closer to the Sun
- DThe barometer is faulty
29.A hydraulic press has a small piston of area 0.005 m² and a large piston of area 0.2 m². A force of 50 N is applied to the small piston. What is the force exerted by the large piston?
Hard
- A2000 N
- B1250 N
- C50 N
- D1.25 N
30.A student measures the pressure at the bottom of a swimming pool. Which of the following changes would increase the pressure at the bottom?
Medium
- AAdding more water to the pool
- BDraining some water from the pool
- CHeating the water
- DAdding salt to dissolve in the water
31.A student performs an experiment to verify the relationship between pressure and depth. They use a U-tube manometer connected to a water tank. They measure the difference in water levels in the manometer at various depths. Which graph best represents the expected relationship between pressure difference (y-axis) and depth (x-axis)?
Hard
- AA straight line through the origin
- BA curve that flattens at greater depths
- CA horizontal line
- DA curve that steepens at greater depths
32.Which of the following is the correct unit for pressure?
Easy
- APascal (Pa)
- BNewton (N)
- CMetre squared (m²)
- DNewton metre (N m)
33.A student investigates how the pressure exerted by a block on a surface varies with the area of contact. They use a block of weight 10 N and place it on different faces. Which of the following experimental results would confirm the relationship Pressure = Force / Area?
Hard
- AWhen area is doubled, pressure halves
- BWhen area is doubled, pressure doubles
- CWhen area is halved, pressure halves
- DPressure is independent of area
34.A water tank has a hole at the bottom. The water emerges at a speed of 4 m/s. If the tank is filled to double the height, what happens to the speed of water emerging? (Assume no energy loss)
Medium
- AIt becomes about 5.66 m/s
- BIt becomes 8 m/s
- CIt becomes 4 m/s
- DIt becomes 2 m/s
35.A student uses a syringe to demonstrate pressure. They fill the syringe with water and push the plunger. Which statement best explains why the water squirts out with force?
Hard
- AThe force on the plunger creates pressure that is transmitted equally throughout the water
- BThe water expands when pushed
- CThe syringe is airtight so the water has nowhere to go
- DThe plunger reduces the volume, increasing the density
36.A student pushes a drawing pin into a noticeboard. The pin exerts a force of 10 N on the board. The area of the pin's tip is 0.00002 m². What is the pressure exerted by the pin on the board?
Easy
- A500,000 Pa
- B50,000 Pa
- C0.000002 Pa
- D200,000 Pa
37.A hydraulic lift uses a small piston of area 0.01 m² and a large piston of area 0.5 m². A force of 100 N is applied to the small piston. What is the force exerted by the large piston?
Hard
- A5000 N
- B200 N
- C500 N
- D2 N
38.In an experiment to measure the pressure at different depths in a liquid, a student uses a pressure sensor attached to a rod. Which of the following should the student do to ensure accurate results?
Medium
- AHold the sensor at each depth for the same amount of time before recording
- BRecord the pressure at the surface first, then at increasing depths
- CMake sure the sensor is facing upwards when taking readings
- DUse a sensor that measures force, not pressure
39.A student investigates how the speed of water emerging from a hole at the bottom of a water tank depends on the height of the water. They measure the speed using a ruler and a stopwatch. Which of the following is the most likely source of error in this experiment?
Hard
- AThe water level in the tank decreases as water flows out, changing the height
- BThe hole is too small for water to flow out
- CThe stopwatch is not accurate enough
- DThe ruler is not long enough to measure the height
40.A student uses a barometer to measure atmospheric pressure at sea level and then on a mountain top. The reading on the mountain top is lower. Which of the following explains this observation?
Medium
- AThe weight of air above the barometer is less on the mountain top
- BThe temperature is lower on the mountain top
- CThe barometer is faulty
- DThe mountain top is closer to the Sun

Revision notes

## Pressure Revision Notes - **Pressure** is a measure of how much force is applied over a given area. - **Equation**: Pressure = Force ÷ Area - **Units**: Force in Newtons (N), Area in metres squared (m²), Pressure in Pascals (Pa) or N/m². ### Key Points - **Liquid pressure**: Increases with depth because more weight of liquid above. - **Atmospheric pressure**: Decreases as altitude increases because less weight of air above. - **Example**: Water shoots out fastest from the bottom hole of a bottle because pressure is greatest there. ### Worked Example A force of 500 N applied over 0.25 m² gives: Pressure = 500 N ÷ 0.25 m² = 2000 Pa ### Quick Calculations - Crate (2600 N, 2 m²): Pressure = 1300 Pa - Book (20 N, 0.02 m²): Pressure = 1000 Pa - Skip (5000 N, 4 m²): Pressure = 1250 Pa - Person (700 N, 0.04 m²): Pressure = 17500 Pa ### Application A high heel shoe sinks more than a trainer because the force (weight) is concentrated on a smaller area, producing greater pressure.

Pressure: A measure of how much force is applied over a given area.
Pascal (Pa): The unit of pressure, equal to one Newton per metre squared (N/m²).
Force: A push or pull measured in Newtons (N).
Area: The surface over which force is distributed, measured in metres squared (m²).
Atmospheric pressure: The pressure exerted by the weight of air above; decreases with increasing altitude.

Flashcards

What is pressure?

Pressure is a measure of how much force is applied over a given area.

What is the equation linking pressure, force and area?

Pressure = Force ÷ Area

What are the units of force, area, and pressure?

Force is measured in Newtons (N), area in metres squared (m²), and pressure in Pascals (Pa) which is N/m².

What happens to atmospheric pressure as height above Earth's surface increases?

Atmospheric pressure decreases as we increase in height because there is less weight of air above us.

In a bottle with holes at different heights, from which hole does water come out fastest?

Water comes out fastest from the lowest hole because it has the most weight of water above it, so the pressure is greatest.

Why does water come out slowly from a hole near the top of a bottle?

Because there is only a small weight of water above that hole, so the pressure is small.

Calculate the pressure when a force of 500 N is applied over an area of 0.25 m².

Pressure = 500 N ÷ 0.25 m² = 2000 Pa.

A crate weighs 2600 N and its base area is 2 m². Calculate the pressure it exerts on the ground.

Pressure = 2600 N ÷ 2 m² = 1300 Pa.

A book weighs 20 N and has an area of 0.02 m². Calculate the pressure it exerts on a table.

Pressure = 20 N ÷ 0.02 m² = 1000 Pa.

A skip weighs 5000 N and its base area is 4 m². Calculate the pressure it exerts on the ground.

Pressure = 5000 N ÷ 4 m² = 1250 Pa.

A person weighs 700 N and their shoes have a combined area of 0.04 m². Calculate the pressure they exert on the ground.

Pressure = 700 N ÷ 0.04 m² = 17500 Pa.

Which will sink more into a wet field: a high heel shoe or a trainer? Why?

The high heel shoe will sink more because it has a smaller area, so the same force (weight) produces a larger pressure.

What is the unit of pressure equivalent to one Newton per metre squared?

Pascal (Pa).

Why does water shoot out faster from the bottom hole of a bottle than from a higher hole?

Because the bottom hole has more weight of water above it, resulting in greater pressure.

What happens to the speed of water coming out of a bottle as the hole is lower?

The speed increases because the pressure increases with depth.

Does pressure in a liquid depend on the weight of liquid above?

Yes, pressure increases with the weight of liquid above.

What is the relationship between force, area, and pressure?

For the same force, a smaller area gives a larger pressure. For the same area, a larger force gives a larger pressure.

A force of 100 N is applied over an area of 0.5 m². Calculate the pressure.

Pressure = 100 N ÷ 0.5 m² = 200 Pa.

A force of 200 N is applied over an area of 0.1 m². Calculate the pressure.

Pressure = 200 N ÷ 0.1 m² = 2000 Pa.

What does Pascal (Pa) stand for?

Pascal is the unit of pressure, equal to one Newton per square metre (N/m²).

Why does atmospheric pressure decrease with altitude?

Because there is less weight of air above as altitude increases.

If you have two holes in a bottle, one at the top and one at the bottom, which has higher water pressure?

The bottom hole has higher water pressure because there is more water above it.

How does pressure change with depth in a liquid?

Pressure increases with depth because the weight of liquid above increases.

What is the formula to calculate pressure?

Pressure = Force ÷ Area.

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