What is pressure in the context of IB MYP Science?

In the IB MYP Science curriculum, pressure is defined as the force exerted per unit area on the surface of an object. It is a fundamental concept in physics, particularly in the study of fluids and gases. Pressure is measured in pascals (Pa) and is crucial for understanding how forces are distributed in different mediums.

How does pressure relate to the behavior of gases?

Pressure plays a significant role in the behavior of gases, as described by the gas laws. According to Boyle's Law, the pressure of a gas is inversely proportional to its volume when temperature is constant. This means that if the volume decreases, the pressure increases, and vice versa. Understanding this relationship helps explain phenomena such as how balloons inflate and how air pressure affects weather patterns.

Why is atmospheric pressure important in the study of heat, light, and sound?

Atmospheric pressure is crucial in the study of heat, light, and sound because it affects how these elements interact with the environment. For instance, changes in atmospheric pressure can influence weather conditions, which in turn affect temperature (heat). Additionally, atmospheric pressure impacts how sound waves travel through the air, as sound speed varies with pressure and temperature. Understanding these interactions is essential for comprehending natural phenomena and technological applications.

What are some real-life applications of pressure in everyday life?

Pressure has numerous real-life applications, including in car tires, where maintaining the correct pressure ensures safety and efficiency. In medicine, blood pressure is a critical health indicator. In cooking, pressure cookers use high pressure to cook food faster. Understanding pressure helps us make informed decisions in these and many other areas of daily life.

How does pressure affect the boiling point of liquids?

Pressure significantly affects the boiling point of liquids. At higher pressures, the boiling point of a liquid increases because more energy is required for the molecules to escape into the vapor phase. Conversely, at lower pressures, such as at high altitudes, the boiling point decreases. This principle is why water boils at a lower temperature on a mountain than at sea level, impacting cooking times and methods.

Why is "Using container height instead of depth in P = ρgh." a common mistake in Pressure?

Why it happens: Students see a tall tank and use the full height. How to avoid it: h is the depth below the LIQUID SURFACE at the point you're calculating. If you're 5 m below the surface, h = 5 m, regardless of how tall the container is.

Why is "Thinking pressure in a fluid only pushes downwards." a common mistake in Pressure?

Why it happens: We think of pressure as being caused by weight pulling down. How to avoid it: At any point in a fluid, pressure pushes EQUALLY in every direction — sideways, up and down.

Why is "Mixing Pa and kPa in calculations." a common mistake in Pressure?

Why it happens: Atmospheric pressure is more naturally quoted in kPa. How to avoid it: Always work in SI units (Pa, N, m²). Convert kPa → Pa by multiplying by 1 000 before substituting.

Heat, light and soundIB MYP Sciences (Years 1-5)

Pressure

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Pressure — IB MYP Sciences: P = F/A, hydrostatic pressure and atmospheric pressure

Why does a sharp knife cut bread easily but a blunt one doesn't? Why does pressure increase as you swim deeper? This MYP Sciences note covers pressure on a surface, pressure in a fluid, atmospheric pressure and useful applications.

What you’ll learn

Mapped to the IB MYP Sciences subject guide (2026 onwards).

MYP Sciences A — Define pressure and state its unit.
MYP Sciences A — Calculate pressure from force and area.
MYP Sciences A — Apply P = ρgh to pressure in a liquid.
MYP Sciences D — Explain everyday examples of small-area / large-area design (snowshoes, knife edges, foundations).
MYP Sciences D — Evaluate the consequences of atmospheric pressure on weather and altitude sickness.

Pressure on a surface

Same force, smaller area — more pressure.

Pressure is the force per unit area:

$P = \frac{F}{A}$

with P in pascals (Pa), F in newtons (N) and A in square metres (m²). 1 Pa = 1 N/m².

This is why design choices matter:

Small area, large pressure. A knife edge focuses your weight onto a thin line — perfect for cutting. A drawing pin's point pushes huge pressure into the wall with very little force.
Large area, small pressure. Snowshoes and skis spread weight over a wide area, reducing pressure so you don't sink into the snow. Camel feet, elephant feet and tractor tyres do the same on soft ground.

Worked example. A box weighs 240 N and sits on a side measuring 0.40 m × 0.30 m. Calculate the pressure on the floor.

A = 0.40 × 0.30 = 0.12 m². P = F/A = 240 / 0.12 = 2 000 Pa = 2 kPa.

Tip the box on its end so the contact area is 0.30 × 0.20 = 0.06 m², and P doubles to 4 kPa for the same weight.

P = F / A. Unit pascal (Pa) = N/m².
Same force, smaller area → larger pressure.
Designs maximise (knives, pins) or minimise (skis, snowshoes) contact area depending on the goal.

Pressure in a fluid

Pressure increases with depth — and pushes equally in every direction.

Imagine being underwater: above you sits a column of water pushing down. The deeper you go, the taller the column and the heavier the water — so the pressure increases.

For a liquid of density ρ at depth h:

$P = \rho \, g \, h$

with P in Pa, ρ in kg/m³, g in N/kg (≈ 9.8 on Earth), h in m.

Three holes in a tank — water shoots furthest from the lowest hole because pressure there is highest.

At any point in a fluid the pressure pushes equally in all directions (up, down, sideways). That's why a fish at depth isn't squashed by water above it — pressure pushes from all sides equally and the inside of the fish pushes back.

Worked example. What is the water pressure 5.0 m below the surface of a pool? Take ρ_water = 1 000 kg/m³, g = 9.8 N/kg.

P = ρgh = 1 000 × 9.8 × 5.0 = 49 000 Pa = 49 kPa.

P = ρ g h for depth h in a fluid.
Pressure increases with depth.
Acts equally in all directions at a given point.

Atmospheric pressure

We live at the bottom of a 100 km column of air — its weight presses on us all the time.

The atmosphere is the layer of air around Earth — kilometres thick. The weight of all that air pressing down on the ground gives atmospheric pressure, about 101 000 Pa = 101 kPa at sea level. That's roughly 100 newtons on every square centimetre.

We don't feel it because our bodies push back with equal pressure from inside.

As you go up a mountain or fly in a plane, there's less air above you, so atmospheric pressure drops:

Sea level: ~101 kPa
Top of Everest (~8 850 m): ~30 kPa
Cruising altitude of a passenger jet (~10 000 m): ~25 kPa (cabins are pressurised to ~80 kPa for comfort)

Atmospheric pressure is what holds liquid in a drinking straw — when you suck, you reduce pressure above the liquid; the higher atmospheric pressure on the rest of the surface pushes it up the straw.

Atmospheric pressure ≈ 101 kPa at sea level.
Drops with altitude — less air above you.
Drinking through a straw works because atmospheric pressure pushes liquid up.

How it’s examined

Criterion A asks for unit conversions and direct P = F/A calculations. Criterion C presents a fluid scenario (a dam, a submarine) and asks you to calculate pressure at a depth. Criterion D may ask you to evaluate a design choice (snowshoes vs hiking boots; thin vs thick handles).

Sources: IB MYP Sciences guide (IBO, official subject guide). Last reviewed 2026-05-25.

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Worked examples, formulae, definitions and the mistakes examiners flag — everything you need to push from a pass to an A*.

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Step-by-step worked examples — Pressure

Step-by-step solutions to past-paper-style questions on pressure, written exactly the way a tutor would explain them at the board.

1Pressure on the floor
Getting started• P = F/A
Question
A wooden crate weighs 600 N. Its base measures 1.0 m × 0.50 m. Calculate the pressure on the floor.
Step-by-step solution
1. Step 1
  Area = 1.0 × 0.50 = 0.50 m².
2. Step 2
  P = F/A = 600 / 0.50 = 1 200 Pa.
Answer
1 200 Pa (1.2 kPa).
2Why use snowshoes?
Getting started• design
Question
A 60 kg person walks on snow. Their boots have a contact area of 0.04 m² together; with snowshoes the area becomes 0.40 m². Compare the pressures.
Step-by-step solution
1. Step 1
  Weight = mg = 60 × 9.8 = 588 N.
2. Step 2
  Boots: P = 588 / 0.04 = 14 700 Pa.
3. Step 3
  Snowshoes: P = 588 / 0.40 = 1 470 Pa — 10× lower.
Answer
Boots: 14.7 kPa. Snowshoes: 1.47 kPa. Snowshoes give 10× less pressure on the snow, so the person doesn't sink.
3Pressure at depth in water
Building confidence• P = ρgh
Question
Calculate the pressure 12 m below the surface of a freshwater lake. Take ρ = 1 000 kg/m³, g = 9.8 N/kg.
Step-by-step solution
1. Step 1
  P = ρgh = 1 000 × 9.8 × 12.
2. Step 2
  P = 117 600 Pa ≈ 118 kPa.
Answer
≈ 118 kPa (relative to atmospheric pressure; total ≈ 219 kPa).
4Atmospheric pressure with altitude
Stretch• atmospheric pressure
Question
Why does atmospheric pressure decrease as you climb a mountain?
Step-by-step solution
1. Step 1
  Atmospheric pressure at a point is caused by the weight of air above that point.
2. Step 2
  Higher up, there is less air above you, so the weight of the air column is less.
3. Step 3
  Therefore the pressure pushing down on you is less.
Answer
Because there is less air ABOVE you at higher altitude, the weight of the atmospheric column — and so the pressure — decreases.

Key Formulae — Pressure

The formulae you need to memorise for pressure on the IB MYP Sciences paper, with every variable defined in plain English and a note on when to use it.

Pressure on a surface
$P = F / A$
$P$
pressure (Pa)
$F$
force (N)
$A$
area (m²)
When to use
Whenever a force pushes on a known area.
Pressure in a fluid
$P = ρ × g × h$
$P$
pressure (Pa)
$ρ$
fluid density (kg/m³)
$g$
gravitational field strength (N/kg)
$h$
depth below surface (m)
When to use
For pressure at a depth h in any liquid (or low-density fluid).

Key Definitions and Keywords — Pressure

Definitions to memorise and the exact keywords mark schemes credit for pressure answers — sharpened from recent examiner reports for the 2026 IB MYP Sciences sitting.

Pressure
Examiner keyword
Force per unit area. P = F/A. Unit pascal (Pa) = N/m².
Pascal (Pa)
SI unit of pressure. 1 Pa = 1 N/m². 1 kPa = 1 000 Pa.
Hydrostatic pressure
Examiner keyword
Pressure in a stationary fluid due to the weight of the fluid above. P = ρgh.
Atmospheric pressure
Examiner keyword
Pressure caused by the weight of air in the atmosphere. About 101 kPa at sea level.

Common Mistakes and Misconceptions — Pressure

The traps other students keep falling into on pressure questions — taken from recent IB MYP Sciences examiner reports and mark schemes — and how to avoid them.

✕Using container height instead of depth in P = ρgh.
Why it happens
Students see a tall tank and use the full height.
How to avoid it
h is the depth below the LIQUID SURFACE at the point you're calculating. If you're 5 m below the surface, h = 5 m, regardless of how tall the container is.
✕Thinking pressure in a fluid only pushes downwards.
Why it happens
We think of pressure as being caused by weight pulling down.
How to avoid it
At any point in a fluid, pressure pushes EQUALLY in every direction — sideways, up and down.
✕Mixing Pa and kPa in calculations.
Why it happens
Atmospheric pressure is more naturally quoted in kPa.
How to avoid it
Always work in SI units (Pa, N, m²). Convert kPa → Pa by multiplying by 1 000 before substituting.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Pressure — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Pressure

Short Study Notes in the form of Slides

Short Study Notes — Pressure

Detailed Notes

What you’ll learn

How it’s examined

1Pressure on the floor

2Why use snowshoes?

3Pressure at depth in water

4Atmospheric pressure with altitude

Pressure on a surface

Pressure in a fluid

Pressure

Pascal (Pa)

Hydrostatic pressure

Atmospheric pressure

✕Using container height instead of depth in P = ρgh.

✕Thinking pressure in a fluid only pushes downwards.

✕Mixing Pa and kPa in calculations.

Practice questions

Past paper style quiz

Assess your understanding

Pressure — frequently asked questions