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KS3 Science · Year 9Chapter 12 · Pressure, forces and motion in depth
Year 9 · Chapter 12

Pressure, forces and motion in depth

By the end of this chapter you will be able to

  • Calculate pressure from force and area, and use units of pascals
  • Explain why pressure in a liquid increases with depth
  • State Newton's third law and give examples of pairs of forces
  • Read a velocity-time graph: gradient for acceleration, area for distance (extension for F = m x a)
  • Explain terminal velocity in terms of balanced forces

You should already know

  • Forces, speed and distance (Year 7 Science, Chapter 11)
  • Pressure in solids and moments (Year 7 Science, Chapter 12)

Where this leads

  • Waves in Chapter 13, which move energy without transferring matter

National Curriculum for England, Key Stage 3 science, Year 9. Content: 9P5 pressure p = F / A in solids (deepens Year 7, Chapter 12), 9P5 pressure in liquids increases with depth and density; atmospheric pressure at the surface and its fall with height (basic), 9P5 Newton's second law F = m x a in simple cases (EXTENSION: top of the KS3 range, flagged), 9P5 Newton's third law as pairs of forces (basic), 9P5 velocity-time graphs: gradient is acceleration, area is distance (deepens Year 7, Chapter 11 and Year 8, Chapter 13), 9P5 terminal velocity (basic).

Exercise P  Do you remember?

1
FWhat is the unit of force? Write the word.
2
FWhat is 5 x 12? Write the number.
3
FWhat is the name of a force that opposes motion between two surfaces? Write the word.
4
FWhat is the speed of an object that travels 60 m in 12 s? Write the number, in m/s.
5
FWhat is the unit of area in the SI system? Write the words.
12.1

Pressure in solids

Year 9
9P5: pressure p = F / A in solids (deepens Year 7, Chapter 12)
Video lesson: Pressure in solidsComing soon
Story. A pupil pushes a drawing pin into a board. The sharp tip makes the pin go in easily. The teacher explains that the same force on a smaller area makes a bigger pressure.

Pressure is the force acting on a surface divided by the area of the surface: p = F / A. The unit of pressure is the pascal, Pa, which is one newton per square metre.

For the same force, a smaller area gives a bigger pressure. This is why a sharp tip works, and why skis spread a skier’s weight over more snow.

Key ideas

  • Pressure = force / area, p = F / A.
  • The unit of pressure is the pascal (Pa), which is N/m2.
  • The same force on a smaller area gives a bigger pressure.
  • Convert cm2 to m2 before using the equation.
Worked example 12.1.1
A force of 600 N acts on an area of 0.5 m2. What is the pressure, in pascals? Write the number.

Method. Use p = F / A.

  1. Write. p = 600 / 0.5.
    600 / 0.5
  2. Calculate. So the pressure is 1200 Pa.
    600 / 0.5 = 1200
  3. Write the answer.
    1200

Check. 1200 x 0.5 = 600 N. ✓

Worked example 12.1.2
A force of 30 N acts on an area of 0.02 m2. What is the pressure, in pascals? Write the number.

Method. Use p = F / A.

  1. Write. p = 30 / 0.02.
    30 / 0.02
  2. Calculate. So the pressure is 1500 Pa.
    30 / 0.02 = 1500
  3. Write the answer.
    1500

Check. 1500 x 0.02 = 30 N. ✓

Worked example 12.1.3
The same 30 N force acts on an area four times as large as 0.02 m2. Is the pressure bigger or smaller? Write the word.

Method. Compare the areas.

  1. Think. A larger area spreads the same force, so the pressure falls.
    spreads the force
  2. Name it. So the pressure is smaller.
    smaller
  3. Write the answer.
    smaller

Check. A bigger area gives less pressure. ✓

Watch out

Watch out: convert area to square metres first. 200 cm2 is 0.02 m2, not 200 m2.

Exam tip

Exam tip. Write the equation, substitute with units, then give the answer in pascals.

Try it (with your teacher, or a grown-up at home). With your teacher, press a finger onto a sheet of paper, then press with a pencil point, and feel the difference. Explain using p = F / A which one has the bigger pressure.

Exercise 12A  Pressure in solids

1
FWhat is the unit of pressure? Write the word.
2
FWrite the equation for pressure. Write the words.
3
FFor the same force, does a smaller area give a bigger or smaller pressure? Write the word.
4
FWhat is one newton per square metre called? Write the word.
5
FWhy do skis reduce the pressure on snow? Write one sentence. Accept any sentence saying they spread the weight over a larger area.
6
PSA force of 100 N acts on an area of 2 m2. What is the pressure, in pascals? Write the number.
7
PSA force of 240 N acts on an area of 0.4 m2. What is the pressure, in pascals? Write the number.
8
PSA block has a weight of 60 N and rests on a base of area 0.2 m2. What is the pressure on the base, in pascals? Write the number. (Use the weight as the force.)
9
PSTwo blocks have the same weight. Block A has an area of 0.1 m2 and block B has 0.4 m2. Which exerts the bigger pressure on the ground? Write the letter.
10
PSA pupil says a shoe with a narrow heel causes more pressure on a floor. Is she right? Write yes or no.
11
RExplain why a sharp knife cuts more easily than a blunt one. Write one sentence. Accept any sentence saying the sharp edge has a smaller area, so the same force gives a bigger pressure.
12
RChallenge: a person of weight 600 N stands on one foot of area 0.02 m2, and then on two feet of total area 0.04 m2. Write the pressure on one foot, in pascals. Write the number.
12.2

Pressure in liquids and the atmosphere

Year 9
9P5: pressure in liquids increases with depth and density; atmospheric pressure at the surface and its fall with height (basic)
Video lesson: Pressure in liquids and the atmosphereComing soon
Story. A pupil makes three holes down the side of a tall plastic bottle and fills it with water. The water jets from the bottom hole travel furthest. The teacher says the pressure increases with depth, so the bottom hole has the greatest pressure.

The pressure in a liquid increases with depth, because there is more liquid above each point. Pressure in a liquid acts in all directions. A denser liquid also gives a greater pressure at the same depth.

The atmosphere is the layer of air above us. Air pressure at sea level is about 100 000 Pa. It falls with height, because there is less air above each point to press down.

top holemiddle holebottom holethe deeper the hole, the further the water jet travels
A container with three holes at increasing depth; deeper holes give a longer water jet
HoleDepth (cm)Water jet distance (cm)
top hole25
middle hole612
bottom hole1020
Depth of each hole and the distance the water jet travels

Key ideas

  • Pressure in a liquid increases with depth.
  • Pressure in a liquid acts in all directions.
  • A denser liquid gives a greater pressure at the same depth.
  • Atmospheric pressure falls with height.
Worked example 12.2.1
Which hole has the greatest water pressure: the top, middle or bottom hole? Write the words.

Method. Compare the depths.

  1. Look. The bottom hole is the deepest.
    deepest
  2. Name it. So the bottom hole has the greatest pressure.
    bottom hole
  3. Write the answer.
    bottom hole

Check. The jet travels furthest from the deepest hole. ✓

Worked example 12.2.2
Does air pressure increase or decrease as you climb a mountain? Write the word.

Method. Think about the air above you.

  1. Think. As you go up, there is less air above you.
    less air above
  2. Name it. So the air pressure decreases.
    decreases
  3. Write the answer.
    decreases

Check. Air pressure falls with height. ✓

Worked example 12.2.3
Is air pressure at sea level about 100 000 Pa or about 100 Pa? Write the number.

Method. Recall the value.

  1. Recall. Air pressure at sea level is about 100 000 Pa.
    100 000 Pa
  2. Name it. So the answer is 100000.
    100000
  3. Write the answer.
    100000

Check. That is about one atmosphere. ✓

Watch out

Watch out: pressure in a liquid is not the same at every point at the same depth only if the liquid is moving; in a still liquid, equal depths have equal pressure.

Exam tip

Exam tip. Link pressure to the weight of the liquid or air above a point: more above, more pressure.

Try it (with your teacher, or a grown-up at home). With your teacher, make three holes in a plastic bottle at different heights. Fill it with water and watch how far each jet travels. Keep the bottle over a tray. Say which hole gives the greatest pressure.

Exercise 12B  Pressure in liquids and the atmosphere

1
FDoes the pressure in a liquid increase or decrease with depth? Write the word.
2
FDoes pressure in a liquid act in all directions? Write yes or no.
3
FDoes air pressure increase or decrease with height? Write the word.
4
FIs the pressure at sea level about 100 000 Pa? Write yes or no.
5
FWhich hole in the container gives the longest water jet: the top or the bottom? Write the word.
6
FDoes a denser liquid give a greater pressure at the same depth? Write yes or no.
7
PSIn the table, how much further does the water jet travel from the bottom hole than from the top hole? Write the number, in cm.
8
PSA hole is at a depth of 10 cm and another at 2 cm. How much deeper is the lower hole, in cm? Write the number.
9
PSAir pressure at sea level is about 100 000 Pa. Would it be bigger or smaller on a high mountain? Write the word.
10
RExplain why a diver feels more pressure in the ears at 20 metres than at 2 metres. Write one sentence. Accept any sentence saying there is more water above, so the pressure is greater.
11
RChallenge: explain why a balloon filled with air bursts less readily at sea level than at the top of a mountain. Accept any sentence saying the air outside is at a greater pressure at sea level, so it pushes in more strongly.
12.3

Newton's third law and balanced forces

Year 9
9P5: Newton's third law as pairs of forces (basic); opposing forces and equilibrium
Video lesson: Newton's third law and balanced forcesComing soon
Story. A pupil pushes against a wall, and feels the wall push back. Her teacher says the two forces are a pair: they are equal and opposite, and they act on different objects.

Newton’s third law says that when one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. These forces are a pair. They act on different objects, so they do not cancel each other out.

Balanced forces act on the same object and cancel out: the object does not accelerate. Unbalanced forces give a resultant force, so the object accelerates.

ABequal and opposite pairA pushes B with the same force that B pushes A
Two objects pushing each other with equal and opposite forces

Key ideas

  • Newton's third law: a pair of equal and opposite forces on different objects.
  • Balanced forces on one object cancel out; the object stays still or moves at a steady speed.
  • Unbalanced forces give a resultant force, and the object accelerates.
  • A pair of forces does not cancel, because they act on different objects.
Worked example 12.3.1
A book rests on a table. The table pushes up on the book with 5 N. What is the weight of the book, if it is balanced? Write the number, in N.

Method. Balanced forces are equal.

  1. Think. The book is balanced, so the two forces are equal.
    equal
  2. Conclude. So the weight of the book is 5 N.
    5
  3. Write the answer.
    5

Check. Balanced forces cancel. ✓

Worked example 12.3.2
A boy pushes a wall with 40 N. What force does the wall exert on the boy? Write the number, in N.

Method. Use Newton's third law.

  1. Think. The wall pushes back with an equal and opposite force.
    equal and opposite
  2. Conclude. So the wall pushes back with 40 N.
    40
  3. Write the answer.
    40

Check. The pair is equal in size. ✓

Worked example 12.3.3
In a pair of forces, does the force on one object cancel the force on the other? Write yes or no.

Method. Recall where the forces act.

  1. Recall. The two forces act on different objects.
    different objects
  2. Decide. So they do not cancel each other; the answer is no.
    no
  3. Write the answer.
    no

Check. Only forces on the same object cancel. ✓

Watch out

Watch out: a pair of forces never cancels, because the two forces act on different objects. Only balanced forces on one object cancel.

Exam tip

Exam tip. When asked about a pair, say “equal and opposite, acting on different objects”.

Try it (with your teacher, or a grown-up at home). With your teacher, sit in two chairs back to back on a smooth floor, and push gently against each other. Say which forces are equal and opposite, and which objects they act on. Do not push hard.

Exercise 12C  Newton's third law and balanced forces

1
FWhat is the name of the law that states that forces come in equal and opposite pairs? Write the words.
2
FDo the two forces in a pair act on the same object? Write yes or no.
3
FAre the forces in a pair equal in size? Write yes or no.
4
FAre the forces in a pair in the same direction or opposite directions? Write the words.
5
FWhat happens to a balanced object: does it accelerate? Write yes or no.
6
PSA book is balanced on a table. Its weight is 5 N. What is the upward force from the table? Write the number, in N.
7
PSA girl pulls a rope with 30 N. What is the force of the rope on the girl? Write the number, in N.
8
PSA force of 12 N to the right and a force of 12 N to the left act on one object. Is there a resultant force? Write yes or no.
9
PSA force of 12 N to the right and 5 N to the left act on one object. What is the resultant force, in N? Write the number.
10
PSA boat is pulled forwards with 200 N and resisted by 200 N of water drag. Is the boat accelerating? Write yes or no.
11
RExplain why a pair of forces between a hand and a wall does not cancel out. Write one sentence. Accept any sentence saying the two forces act on different objects.
12
RChallenge: a rocket pushes gas downwards with 500 N. Write the force of the gas on the rocket, and say which direction it acts. Accept 500 N upwards, because it is equal and opposite to the push on the gas.
12.4

Newton's second law (extension)

Year 9
9P5: Newton's second law F = m x a in simple cases (EXTENSION: top of the KS3 range; flagged)
Video lesson: Newton's second law (extension)Coming soon
Story. A trolley is pushed with a larger force, and it speeds up faster. A heavier trolley speeds up more slowly with the same push. The teacher says these two observations can be written as one equation, F = m x a. This section is an extension.

Extension (top of the KS3 range; flagged). Newton’s second law says that the resultant force on an object equals its mass times its acceleration: F = m x a. F is in newtons, m in kilograms and a in metres per second squared (m/s2). A larger force gives a larger acceleration; a larger mass gives a smaller acceleration.

Key ideas

  • Extension: F = m x a, with F in N, m in kg, and a in m/s2.
  • A bigger resultant force gives a bigger acceleration.
  • A bigger mass gives a smaller acceleration for the same force.
  • Acceleration is zero when the forces are balanced.
Worked example 12.4.1
A 4 kg object has a resultant force of 12 N. What is its acceleration, in m/s2? Write the number. (Extension.)

Method. Rearrange F = m x a to a = F / m.

  1. Rearrange. a = F / m = 12 / 4.
    12 / 4
  2. Calculate. So the acceleration is 3 m/s2.
    12 / 4 = 3
  3. Write the answer.
    3

Check. 4 x 3 = 12 N. ✓

Worked example 12.4.2
A 5 kg car has a resultant force of 20 N. What is its acceleration? Write the number, in m/s2. (Extension.)

Method. Use a = F / m.

  1. Calculate. a = 20 / 5 = 4.
    20 / 5 = 4
  2. Conclude. So the acceleration is 4 m/s2.
    4
  3. Write the answer.
    4

Check. 5 x 4 = 20 N. ✓

Worked example 12.4.3
A 6 kg object is on Earth, where g is 10 N/kg. What is its weight, in newtons? Write the number.

Method. Use W = m x g.

  1. Write. W = 6 x 10.
    6 x 10
  2. Calculate. So the weight is 60 N.
    6 x 10 = 60
  3. Write the answer.
    60

Check. 60 / 10 = 6 kg. ✓

Watch out

Watch out: F = m x a uses the resultant force, not one of the separate forces. Work out the resultant first.

Exam tip

Exam tip. Rearrange first: a = F / m, or m = F / a. Write the units with each number.

Try it (with your teacher, or a grown-up at home). With your teacher, push a trolley with the same push first empty, then with a 1 kg mass on it. Use a stopwatch and a metre rule to see which one speeds up more. Say which variable is the force and which is the mass.

Exercise 12D  Newton's second law (extension)

1
FWhat is the equation linking force, mass and acceleration? Write the words. (Extension.)
2
FIn F = m x a, what is the unit of force? Write the word. (Extension.)
3
FDoes a bigger resultant force give a bigger or smaller acceleration? Write the word. (Extension.)
4
FDoes a bigger mass give a bigger or smaller acceleration for the same force? Write the word. (Extension.)
5
PSA 4 kg object has a resultant force of 12 N. Find its acceleration, in m/s2. (Extension.) Write the number.
6
PSA 5 kg car has a resultant force of 20 N. Find its acceleration. (Extension.) Write the number, in m/s2.
7
PSA 2 kg object accelerates at 3 m/s2. What is the resultant force, in newtons? (Extension.) Write the number.
8
PSA resultant force of 30 N gives an object an acceleration of 5 m/s2. What is its mass, in kg? (Extension.) Write the number.
9
PSA 6 kg object is on Earth. What is its weight, in newtons, with g = 10 N/kg? Write the number.
10
PSTwo forces act on a 3 kg object: 15 N to the right and 3 N to the left. Find the acceleration. (Extension.) Write the number, in m/s2.
11
RExplain why a heavy lorry takes longer to speed up than a small car, with the same engine force. Write one sentence. (Extension.) Accept any sentence saying the lorry has a bigger mass, so the same force gives a smaller acceleration.
12
RChallenge: a constant resultant force of 10 N acts on a 2 kg object at rest. Find its speed after 3 s, if the acceleration stays the same. (Extension.) Write the number, in m/s.
12.5

Velocity-time graphs and terminal velocity

Year 9
9P5: velocity-time graphs: gradient is acceleration, area is distance; terminal velocity (basic)
Video lesson: Velocity-time graphs and terminal velocityComing soon
Story. A bike rides from rest, cruises at a steady speed, and then brakes to a stop. The class plots a velocity-time graph of the ride. They use it to find the acceleration and the total distance.

On a velocity-time graph, the gradient (the slope) is the acceleration. A horizontal line means a steady speed, with zero acceleration. The area under the graph is the distance travelled. A steep downward slope means the object is slowing down quickly.

Terminal velocity is the steady speed reached by a falling object when the drag force equals its weight. The forces are balanced, so the acceleration is zero.

Velocity against time for a bike0369121518024681012time (s)velocity (m/s)area = distancesteady
Velocity-time graph for a bike: speeds up, cruises steadily, then slows to a stop
Part of the journeyStarts (m/s)Ends (m/s)Time (s)
speeding up0105
steady101010
slowing down1002
The three parts of the bike journey

Key ideas

  • Gradient of a velocity-time graph = acceleration.
  • Area under a velocity-time graph = distance.
  • A horizontal line means steady speed (zero acceleration).
  • Terminal velocity: drag equals weight, so the forces balance.
Worked example 12.5.1
In the first part of the bike journey, the speed rises from 0 to 10 m/s in 5 s. What is the acceleration? Write the number, in m/s2.

Method. Gradient = change in velocity / time.

  1. Calculate. (10 - 0) / (5 - 0) = 10 / 5.
    10 / 5
  2. Conclude. So the acceleration is 2 m/s2.
    10 / 5 = 2
  3. Write the answer.
    2

Check. 2 x 5 = 10 m/s. ✓

Worked example 12.5.2
In the steady part, the bike rides at 10 m/s for 10 s. How far does it go? Write the number, in m.

Method. Area = speed x time for a steady speed.

  1. Calculate. Distance = 10 x 10 = 100 m.
    10 x 10
  2. Conclude. So the bike goes 100 m at a steady speed.
    100
  3. Write the answer.
    100

Check. 100 / 10 = 10 m/s. ✓

Worked example 12.5.3
In the first part, the distance is the area of a triangle with base 5 s and height 10 m/s. Find the distance, in m.

Method. Area of a triangle = half x base x height.

  1. Calculate. Area = 0.5 x 5 x 10 = 25.
    0.5 x 5 x 10
  2. Conclude. So the distance is 25 m.
    25
  3. Write the answer.
    25

Check. 25 m is the first part of the journey. ✓

Watch out

Watch out: the gradient gives acceleration, not distance. The area under the graph gives distance.

Exam tip

Exam tip. For a steady speed, distance = speed x time. For a triangle under the graph, use half x base x height.

Try it (with your teacher, or a grown-up at home). With your teacher, roll a toy car down a ramp, and record its position every second with a stopwatch and a metre rule. Plot distance against time, and then plot a velocity-time graph. Say what the gradient of the second graph shows.

Exercise 12E  Velocity-time graphs and terminal velocity

1
FOn a velocity-time graph, what does the gradient show? Write the word.
2
FOn a velocity-time graph, what does the area under the graph show? Write the word.
3
FWhat does a horizontal line on a velocity-time graph show? Write the words.
4
FWhat is the name of the steady speed reached by a falling object when drag equals its weight? Write the words.
5
FAt terminal velocity, is the acceleration zero? Write yes or no.
6
PSIn the bike graph, how long is the steady part? Write the number, in s.
7
PSIn the braking part, the speed falls from 10 m/s to 0 in 2 s. What is the acceleration? Write the number, in m/s2. (Use the magnitude.)
8
PSUsing the three parts of the bike journey, what is the total distance, in m? Write the number.
9
PSA sprinter reaches 8 m/s in 4 s from rest. What is the acceleration? Write the number, in m/s2.
10
PSA cyclist cruises at 8 m/s for 10 s. How far does she travel, in m? Write the number.
11
RExplain why a falling parachutist reaches a terminal velocity. Write one sentence. Accept any sentence saying the air resistance grows until it equals the weight, and the forces balance.
12
RChallenge: explain why a falling object with air resistance does not keep accelerating for ever. Accept any sentence saying the drag increases with speed, until it balances the weight.

Chapter summary

SkillMethod
Pressure in solidsp = F / A, in pascals; a smaller area gives a bigger pressure.
Pressure in liquids and airLiquid pressure increases with depth and acts in all directions; air pressure falls with height.
Newton's third lawEqual and opposite forces in pairs, acting on different objects; they do not cancel.
Newton's second law (extension)F = m x a, with F in N, m in kg and a in m/s squared.
Velocity-time graphsGradient is acceleration; area is distance; horizontal means steady speed.
Terminal velocityDrag equals weight; the forces balance; the speed is steady.

Can you…?

  • I can calculate pressure from force and area, in pascals
  • I can explain why liquid pressure increases with depth, and why air pressure falls with height
  • I can state Newton's third law and give examples of pairs of forces
  • I can read a velocity-time graph: gradient for acceleration, area for distance
  • I can explain terminal velocity in terms of balanced forces

Key terms

pressure
force divided by the area it acts on, measured in pascals
pascal
the unit of pressure: one newton per square metre
atmosphere
the layer of air around the Earth
Newton's third law
the force on one object by another is equal and opposite to the force on the other by the first
balanced forces
forces that cancel out, so there is no resultant force
resultant force
the single force that is equivalent to all the forces acting
acceleration
the change in velocity each second
velocity-time graph
a graph of speed or velocity against time: the gradient is acceleration and the area is distance
drag
the force that opposes motion through air or water
terminal velocity
the steady speed reached when drag equals weight

Exercise 12Z  Check-up

1
What is the unit of pressure? Write the word.
2
Calculate the pressure from a force of 240 N on 0.4 m2. Write the number, in pascals.
3
Does pressure in a liquid increase or decrease with depth? Write the word.
4
Does air pressure fall with height? Write yes or no.
5
What is the name of the law stating that forces come in equal and opposite pairs? Write the words.
6
What is the resultant force of 12 N to the right and 5 N to the left, in N? Write the number.
7
On a velocity-time graph, what does the gradient show? Write the word.
8
A velocity-time graph rises from 0 to 10 m/s in 5 s. What is the acceleration? Write the number, in m/s2.
9
What is the name of the steady speed reached when drag equals weight? Write the words.
10
Explain why a pair of equal and opposite forces does not cancel. Write one sentence. Accept any sentence saying the forces act on different objects.

Total 21 marks. Allow about 21 minutes.

Exercise 12X  Practice test questions

1
FWhat is the equation for pressure? Write the words.[1 mark]
2
FDoes air pressure increase or decrease at a high altitude? Write the word.[1 mark]
3
PSA force of 600 N acts on 0.5 m2. Calculate the pressure, in pascals. Write the number.[2 marks]
4
PSA boy pushes a wall with 40 N. What force does the wall exert on him? Write the number, in N.[1 mark]
5
PSA 4 kg object has a resultant force of 12 N. Calculate its acceleration, in m/s2. (Extension.) Write the number.[2 marks]
6
RExplain why pressure in a liquid is greater at the bottom of a tank than at the top. Write one sentence. Accept any sentence saying there is more liquid above the bottom, so the pressure is greater.[2 marks]
7
PSA velocity-time graph shows a steady speed of 10 m/s for 10 s. How far is travelled, in m? Write the number.[2 marks]
8
RDescribe the forces when a parachutist reaches terminal velocity. Write two sentences. Accept any answer saying the drag equals the weight, so the forces balance and the speed is steady.[3 marks]
9
PSA 2 kg object is pushed with a resultant force of 10 N. Find its acceleration. (Extension.) Write the number, in m/s2.[2 marks]
10
FName the force that opposes motion between a moving object and the air, and say how it changes as an object speeds up. Write two sentences. Accept any answer naming drag or air resistance, which increases with speed.[2 marks]
11
PSA force of 30 N acts on an area of 0.02 m2. Find the pressure, in pascals, and say whether a bigger area would give a bigger or smaller pressure. Write the number, then the word.[3 marks]
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