Motion and Pressure Study Pack

Key Knowledge

Motion and pressure are linked by forces. A force can start an object moving, slow it down, change its direction, change its shape, or squash it into a surface. Motion describes how an object's position changes over time. Pressure describes how a force is spread over an area. Floating and sinking depend on forces too: weight pulls an object down, while upthrust from a fluid pushes it up.

This pack covers:

• describing motion using distance, time, and speed
• using distance-time graphs
• explaining balanced and unbalanced forces
• calculating pressure
• explaining pressure in solids, liquids, and gases
• using density, upthrust, and buoyancy to explain floating and sinking
• planning and evaluating practical investigations

What Is Motion?

Motion is a change in position over time. If an object is moving, its position is changing compared with a reference point. A reference point is something you compare the motion with, such as a classroom wall, a starting line, a bus stop, or your home.

For example:

• A pupil walking away from school is moving because their position changes compared with the school gate.
• A book on a desk is stationary because its position is not changing compared with the desk.
• A train may feel still to passengers inside it, but it is moving compared with the platform.

Motion can be described in several ways:

• constant speed: the object travels equal distances in equal times
• changing speed: the object covers different distances in equal times
• acceleration: the object speeds up
• deceleration: the object slows down
• stationary: the object is not changing position

At KS3, speed means how fast something moves. At higher levels, velocity means speed in a particular direction. For this pack, speed does not include direction unless a question says otherwise.

Distance, Time, and Speed

Distance is how far an object travels. Common units are metres (m) and kilometres (km). A metre is sensible for a classroom, a running track, or a trolley on a ramp. A kilometre is sensible for longer journeys, such as a bus route or train journey.

Time is how long a journey or event takes. Common units are seconds (s), minutes (min), and hours (h). Seconds are useful for short events, minutes for everyday journeys, and hours for long trips.

Speed is distance travelled per unit time. It tells you how much distance is covered every second, minute, or hour.

Quantity	Meaning	Common units
distance	how far an object travels	metre (m), kilometre (km)
time	how long a journey or event takes	second (s), minute (min), hour (h)
speed	distance travelled per unit time	metre per second (m/s), kilometre per hour (km/h)
force	a push or pull	newton (N)
area	size of a surface	square metre (m2)
pressure	force spread over an area	pascal (Pa), N/m2
mass	amount of matter in an object	kilogram (kg), gram (g)
volume	amount of space an object takes up	cm3, m3
density	mass per unit volume	g/cm3 or kg/m3, used simply at KS3

Sensible speed units depend on the situation.

Example	Sensible unit	Approximate speed
walking pupil	m/s	1-2 m/s
running pupil	m/s	4-8 m/s
cyclist	m/s or km/h	5-10 m/s
bus in town	km/h or m/s	about 30 km/h
train	km/h	80-200 km/h
falling object in a lab	m/s	changes each second

Calculating Speed

The speed equation is:

speed = distance / time

You can also rearrange it:

distance = speed x time
time = distance / speed

An equation summary can help:

If you need to find...	Use...	Example units
speed	distance / time	m/s or km/h
distance	speed x time	m or km
time	distance / speed	s or h

Worked Example 1: Speed of a Cyclist

A cyclist travels 120 m in 20 s. Calculate the cyclist's speed.

1. Write the equation:

speed = distance / time

2. Substitute the values:

speed = 120 m / 20 s

3. Calculate:

speed = 6 m/s

The cyclist's speed is 6 m/s.

Worked Example 2: Distance Travelled by a Bus

A bus moves at 12 m/s for 30 s. Calculate the distance travelled.

1. Write the equation:

distance = speed x time

2. Substitute the values:

distance = 12 m/s x 30 s

3. Calculate:

distance = 360 m

The bus travels 360 m.

Worked Example 3: Time Taken by a Runner

A runner travels 400 m at 8 m/s. Calculate the time taken.

1. Write the equation:

time = distance / speed

2. Substitute the values:

time = 400 m / 8 m/s

3. Calculate:

time = 50 s

The runner takes 50 s.

Comparing Speeds

Object	Distance	Time	Speed
walking pupil	100 m	80 s	1.25 m/s
cyclist	120 m	20 s	6 m/s
bus	360 m	30 s	12 m/s
train	1000 m	25 s	40 m/s

The train is fastest because it travels the greatest distance each second. The walking pupil is slowest because the distance travelled each second is smallest.

Interpreting Distance-Time Graphs

A distance-time graph shows how the distance from a starting point changes over time. Time usually goes on the horizontal x-axis. Distance usually goes on the vertical y-axis.

Distance (m)
  |
  |             C
  |          /
  |   B____/
  |  /
  | /
  +---------------- Time (s)
    A

On a distance-time graph:

• a rising line means the object is moving away from the starting point
• a horizontal line means the object is stationary
• a steeper line means a greater speed
• a curved line means the speed is changing
• a line sloping down means the object is returning towards the starting point

A steeper line does not mean higher pressure. It means the distance is changing more quickly each second.

Graph feature	Meaning
rising straight line	moving at constant speed away from the start
steeper rising straight line	moving at a higher constant speed
horizontal line	stationary; distance stays the same as time passes
curved line becoming steeper	accelerating; speed is increasing
curved line becoming less steep	decelerating; speed is decreasing

Worked Example 4: Journey Description

A pupil walks away from home for 5 minutes, stops at a shop for 3 minutes, then walks farther away from home for 4 minutes.

On a distance-time graph:

• the first section is a rising line because the pupil moves away from home
• the second section is horizontal because the pupil stops at the shop
• the third section is another rising line because the pupil walks farther away

If the third rising line is steeper than the first, the pupil walked faster after leaving the shop.

Worked Example 5: Speed from a Graph

A straight section of a graph goes from 0 m at 0 s to 40 m at 10 s.

speed = distance / time
speed = 40 m / 10 s
speed = 4 m/s

The speed is 4 m/s.

Worked Example 6: Comparing Two Lines

Object A travels 30 m in 10 s. Object B travels 50 m in 10 s.

speed of A = 30 m / 10 s = 3 m/s
speed of B = 50 m / 10 s = 5 m/s

Object B is faster because its line is steeper and its calculated speed is higher.

Worked Example 7: Horizontal Lines

If a graph is horizontal from 20 s to 40 s, time is still passing. The object is stationary because the distance from the start is not changing. A horizontal line does not mean zero time. It means zero speed during that section.

Forces and Motion

A force is a push or pull. Forces are measured in newtons (N). Forces can:

• start an object moving
• stop an object
• speed an object up
• slow an object down
• change an object's direction
• change an object's shape

Some forces need contact between objects. These are contact forces. Examples include friction, air resistance, water resistance, normal reaction, and applied force. Other forces act without contact. These are non-contact forces. Examples include gravity and magnetism.

Force	Type	What it does
weight	non-contact	pulls an object down due to gravity
normal reaction	contact	pushes up from a surface
friction	contact	acts against sliding or attempted sliding
air resistance	contact	acts against motion through air
water resistance	contact	acts against motion through water
upthrust	contact	upward force from a fluid
applied force	contact	push or pull from a person or object

A car braking is a useful example. The engine may provide a driving force forwards. When the driver brakes, friction in the brakes and friction between tyres and the road act against the motion. If the backward forces are greater than the forward driving force, the car decelerates.

A streamlined cyclist, swimmer, or falling object has a shape that reduces drag. Drag is resistance from air or water. Reducing drag can help an object move faster for the same driving force.

Balanced and Unbalanced Forces

Balanced forces are equal in size and opposite in direction. They do not change an object's speed or direction. The object may be stationary, or it may be moving at a constant speed in a straight line.

          Normal reaction
               ^
               |
        [ box on table ]
               |
               v
             Weight

In the diagram, the normal reaction pushes up and the weight pulls down. If the two forces are equal, the forces are balanced. The box does not accelerate up or down.

Unbalanced forces are not equal. They cause acceleration, deceleration, or a change in direction.

Friction/drag <---- [ trolley ] ----> Pulling force

If the pulling force is larger than friction, the trolley accelerates forwards. If friction is larger than the pulling force, the trolley decelerates.

Situation	Forces	Effect on motion
book resting on a table	balanced vertical forces	remains stationary
car moving at steady speed	driving force equals drag and friction	continues at constant speed
trolley pulled harder than friction	unbalanced force forwards	accelerates forwards
cyclist stops pedalling	drag and friction greater than driving force	decelerates
ball changing direction	unbalanced sideways force	direction changes

Parachutist Example

Before parachute opens:

      Air resistance
           ^
           |
        [person]
           |
           v
         Weight

Weight is larger, so the parachutist accelerates downwards.

After parachute opens:

       Large air resistance
              ^
              |
        [parachute]
           [person]
              |
              v
            Weight

Air resistance increases, so the parachutist slows down.

At first, weight is greater than air resistance, so the parachutist speeds up. As speed increases, air resistance increases. When air resistance equals weight, the forces are balanced and the parachutist falls at constant speed. When the parachute opens, air resistance suddenly becomes much larger than weight, so the parachutist decelerates. Later, the forces may balance again at a lower constant speed.

What Is Pressure?

Pressure is force spread over an area. The same force can produce different pressures depending on the contact area.

pressure = force / area

Pressure is measured in newtons per square metre (N/m2), also called pascals (Pa).

1 Pa = 1 N/m2

Pressure is not the same as force. Force is a push or pull. Pressure depends on both force and area.

If this changes...	What happens to pressure?
force increases and area stays the same	pressure increases
force decreases and area stays the same	pressure decreases
area increases and force stays the same	pressure decreases
area decreases and force stays the same	pressure increases

Calculating Pressure

The pressure equation is:

pressure = force / area

If you need to find...	Use...	Example units
pressure	force / area	Pa or N/m2
force	pressure x area	N
area	force / pressure	m2

Worked Example 8: Basic Pressure Calculation

A 50 N force acts over an area of 0.5 m2. Calculate the pressure.

1. Write the equation:

pressure = force / area

2. Substitute the values:

pressure = 50 N / 0.5 m2

3. Calculate:

pressure = 100 N/m2

The pressure is 100 N/m2, or 100 Pa.

Worked Example 9: Same Force, Different Areas

A 60 N force acts on two different areas.

Situation	Force	Area	Pressure
small area	60 N	0.2 m2	300 N/m2
large area	60 N	1.0 m2	60 N/m2

The same force produces higher pressure on the smaller area because the force is concentrated onto less surface.

Same force down        Same force down
      v                      v
    [__]                  [________]
 small area              large area
 high pressure           lower pressure

Worked Example 10: School Bag Strap

A school bag strap pushes down on a shoulder with a force of 40 N. A narrow strap has a contact area of 0.02 m2.

pressure = force / area
pressure = 40 N / 0.02 m2
pressure = 2000 N/m2

If a wider strap spreads the same force over 0.08 m2:

pressure = 40 N / 0.08 m2
pressure = 500 N/m2

The wider strap is more comfortable because it produces lower pressure on the shoulder.

Pressure in Solids

Pressure in solids is important when a force acts through a contact area. A drawing pin enters a noticeboard easily because the point has a very small area. The same push from your thumb creates a very high pressure at the point of the pin.

A blunt object with the same force has a larger contact area, so the pressure is lower. It is less likely to enter the board.

Example	Contact area	Pressure effect
sharp knife	small edge area	high pressure, cuts more easily
blunt knife	larger edge area	lower pressure, cuts less easily
drawing pin point	tiny area	very high pressure at the point
thumb on pin head	larger area	lower pressure on the thumb
high heel	small area	high pressure on the floor
snowshoe	large area	lower pressure on snow
ski	large area	lower pressure, less sinking into snow
wide tyre	large contact area	lower pressure on soft ground

Trainers spread weight over a fairly large sole area. Football boots have studs that increase pressure at points, helping grip in grass. High heels can damage soft floors because the wearer's weight is concentrated onto a small area. Snowshoes spread the person's weight over a large area, so the pressure on snow is lower.

Pressure in Liquids and Gases

Liquids and gases are fluids. A fluid can flow. Pressure in a fluid acts in all directions, not only downwards.

Gas pressure happens because gas particles move quickly and collide with surfaces. In a balloon, air particles collide with the inside of the balloon and push outwards. Tyres and air beds work because compressed air inside them produces pressure.

Liquid pressure increases with depth. This is because deeper water has more water above it pressing down, so the pressure is greater. Water pressure also depends on the density of the liquid. Denser liquids produce greater pressure at the same depth, but at KS3 you mainly need to know that pressure increases as depth increases.

Water surface
----------------
  low pressure

  medium pressure

  high pressure
----------------
Bottom

This explains why your ears may feel pressure when diving deeper in a swimming pool. It also explains why dam walls are often thicker at the bottom. The bottom of the dam must withstand greater water pressure than the top.

Fluid pressure can be linked to motion. Swimmers and submarines experience water resistance as they move through water. Streamlined shapes reduce drag, helping them move more easily through the fluid. Submarines also need to withstand high water pressure when they travel deep underwater.

Density, Upthrust, and Buoyancy

Density describes how much mass is packed into a certain volume. A material with high density has a lot of mass in a small space. A material with low density has less mass in the same space.

At KS3, you can think of density as:

density = mass per unit volume

Density is not the same as weight. Mass is the amount of matter in an object. Weight is the force caused by gravity pulling on that mass. Density compares mass with volume.

Upthrust is the upward force from a fluid. A fluid can be a liquid or a gas. Buoyancy is the effect of upthrust helping objects float.

        Upthrust
           ^
           |
      [ floating block ]
~~~~~~~~ water ~~~~~~~~
           |
           v
         Weight

If upthrust balances weight, the object floats or stays at a steady depth. If weight is greater than upthrust, the object sinks.

        Small upthrust
             ^
             |
          [ coin ]
~~~~~~~~~ water ~~~~~~~~~
             |
             v
        Larger weight

The coin sinks because weight is greater than upthrust.

Floating and Sinking

Floating and sinking depend on density, weight, upthrust, shape, volume, and displaced water. Displaced water is water pushed out of the way by an object.

Situation	Result
weight greater than upthrust	object sinks
upthrust equal to weight	object floats or stays at constant depth
density greater than water	object tends to sink
average density less than water	object tends to float

A wooden block floats because its density is usually less than the density of water. A metal coin sinks because it has high density and does not displace enough water to create an upthrust equal to its weight.

A boat floats when upthrust balances its weight. It may be heavy, but it has a large volume and displaces a lot of water. Many boats also contain air, so their average density is lower than the density of solid metal.

A steel nail sinks because it is small, dense, and displaces only a small volume of water. A steel ship floats because its shape gives it a large volume and it contains air. The ship's average density, including the air inside, is low enough for it to displace enough water and produce a balancing upthrust.

Oil floating on water is another density example. Many oils are less dense than water, so they form a layer on top. A plastic bottle with trapped air floats because the air lowers its average density. A life jacket helps a person float because it adds volume and trapped air without adding much weight.

Submarine Ballast Tanks

Submarines change their average density using ballast tanks. When the tanks fill with water, the submarine becomes denser and sinks. When compressed air pushes water out of the tanks, the submarine becomes less dense and rises.

Submarine rising                 Submarine sinking

   air in tanks                     water in tanks
  ______________                   ______________
 /              \                 /              \
|  AIR      AIR  |               | WATER  WATER  |
|                |               |                |
 \______________/                 \______________/
 average density lower            average density higher
 more likely to rise               more likely to sink

Practical Investigation Skills

Good science investigations are fair, repeatable, and carefully measured.

The independent variable is the variable you change. The dependent variable is the variable you measure. Control variables are kept the same to make the test fair.

Repeatability means the same person can repeat the method and get similar results. Reliability is improved when repeated results are consistent. Accuracy means closeness to the true value. Precision means measurements are close together or measured using small scale divisions. Repeats improve reliability, but they do not automatically remove systematic errors, such as a force meter that was not zeroed.

Investigation	Independent variable	Dependent variable	Control variables
trolley on a ramp	ramp height or slope angle	time taken or speed	trolley, distance, surface, release method
pressure from a block	contact area of block	depth of mark in soft surface	force/weight, material, surface, measuring method

Planning Task: Area and Pressure

Question: How does the area of a block affect the pressure it exerts on a soft surface?

Possible method:

1. Place a tray of soft modelling clay or sand on a flat bench.
2. Use the same rectangular block each time.
3. Put the block on the surface with its smallest face touching the clay.
4. Add the same mass on top of the block each time so the force stays the same.
5. Leave the block for 10 seconds.
6. Remove the block and measure the depth of the mark.
7. Repeat three times and calculate a mean depth.
8. Repeat using the block on larger faces.

Variables:

Variable type	Example
independent variable	contact area of the block
dependent variable	depth of mark in the soft surface
control variables	weight of block and masses, type of surface, time left on surface, measuring tool

Safety:

• Keep masses low so they do not fall or crush fingers.
• Place masses gently.
• Keep the tray stable on the bench.

Evaluation:

• Repeat each measurement to spot anomalies.
• Use a ruler with small divisions to improve precision.
• Smooth the clay or sand between repeats.
• Keep the same force to make the test fair.
• A limitation is that clay may not reset perfectly between trials.

Expected result: a smaller contact area should make a deeper mark because the same force produces greater pressure.

Key Vocabulary

Term	Meaning
motion	change in position over time
distance	how far an object travels
time	how long an event or journey takes
speed	distance travelled per unit time
constant speed	travelling equal distances in equal times
acceleration	speeding up
deceleration	slowing down
stationary	not changing position
distance-time graph	graph showing distance from a start point against time
force	a push or pull, measured in newtons
balanced forces	equal forces in opposite directions causing no change in motion
unbalanced forces	forces that cause acceleration, deceleration, or direction change
friction	force opposing sliding or attempted sliding
air resistance	force opposing motion through air
water resistance	force opposing motion through water
weight	force of gravity on an object
normal reaction	support force from a surface
pressure	force spread over an area
pascal	unit of pressure equal to 1 N/m2
fluid	liquid or gas
density	mass per unit volume
upthrust	upward force from a fluid
buoyancy	the floating effect caused by upthrust
displaced water	water pushed out of the way by an object
independent variable	variable changed in an investigation
dependent variable	variable measured in an investigation
control variable	variable kept the same for a fair test
anomaly	result that does not fit the pattern
reliability	confidence improved by consistent repeats

Common Misconceptions

Wrong idea	Correct idea	Example
Speed and velocity are always the same.	At KS3, speed is how fast something moves; velocity includes direction at higher levels.	10 m/s is a speed; 10 m/s north is a velocity.
A horizontal line on a distance-time graph means time has stopped.	It means the object is stationary while time continues.	A pupil waits at a shop for 3 minutes.
A steeper distance-time graph means higher pressure.	A steeper line means greater speed.	50 m in 10 s is faster than 20 m in 10 s.
A downward sloping distance-time graph means travelling backwards in time.	It usually means returning towards the starting point.	A pupil walks back home.
A force is needed to keep moving at constant speed.	If forces are balanced, motion does not change.	A train at steady speed has balanced driving force and drag.
Balanced forces always mean stationary.	Balanced forces can also mean constant speed in a straight line.	A cyclist travelling steadily.
Heavier objects always fall faster.	Air resistance and shape can affect falling.	A flat paper sheet falls differently from a crumpled one.
Heavier objects always sink.	Floating depends on density, volume, displaced water, weight, and upthrust.	A heavy ship can float.
Large objects must sink.	Large objects can float if their average density is low enough.	A plastic bottle filled with air floats.
A metal ship should sink because metal is dense.	The ship contains air and displaces much water, so its average density can be low enough.	Steel ship compared with steel nail.
Pressure is the same as force.	Pressure is force divided by area.	Same force on a pin point gives high pressure.
Increasing area increases pressure.	Increasing area lowers pressure if force stays the same.	Snowshoes lower pressure on snow.
Sharp objects cut by using more force automatically.	Sharp objects create higher pressure with the same force because the area is smaller.	Sharp knife compared with blunt knife.
Liquid pressure only depends on the total amount of water.	Liquid pressure increases with depth.	Dam walls are thicker at the bottom.
Fluid pressure only acts downwards.	Fluid pressure acts in all directions.	Air pressure pushes outwards inside a balloon.
Density is the same as weight.	Density compares mass with volume; weight is a force.	A small metal coin can be denser than a large wooden block.
Repeats remove every error.	Repeats improve reliability but not all systematic errors.	A badly zeroed force meter still gives wrong readings.

Real-World Applications

Motion and pressure appear in everyday life.

A pupil walking, stopping, and running to school can be described using a distance-time graph. The walking section has a gentle rising line, the stop has a horizontal line, and the running section has a steeper rising line.

Vehicles are designed using forces and motion. A car needs a driving force to accelerate. Friction in the brakes helps it slow down. Tyres are designed to grip the road, especially when braking or turning. Trains often travel faster than buses because they can cover more distance each second.

Pressure explains why footwear has different designs. Trainers spread weight over a comfortable area. Football boots use studs to increase pressure on the ground and improve grip. Skis and snowshoes reduce pressure by spreading weight over a large area. High heels increase pressure because the contact area is small.

Sharp knives, drawing pins, and needles use high pressure from small areas. A sharp knife cuts because the force is concentrated along a thin edge. A drawing pin enters a board because the point has a tiny area, while the wider head spreads the force on your thumb.

Fluid pressure matters in swimming, diving, dams, tyres, balloons, and air beds. Water pressure increases with depth, so your ears may feel pressure deeper underwater. Dam walls are thicker near the bottom because pressure is greater there. Gas pressure in tyres supports the weight of a vehicle.

Floating and sinking are important for boats, submarines, life jackets, and floating bottles. A life jacket increases volume and traps air, helping upthrust balance a person's weight. A submarine controls its average density using ballast tanks.

Diagram and Data Interpretation

Task 1: Distance-Time Table

A pupil walks away from school, stops, then runs.

Time (s)	Distance from school (m)
0	0
10	12
20	24
30	36
40	36
50	36
60	66
70	96

Questions:

1. Plot these results on a distance-time graph.
2. Identify the stationary section.
3. Calculate the speed from 0 s to 30 s.
4. Calculate the speed from 50 s to 70 s.
5. Which section is fastest? Use evidence.
6. Suggest one limitation or improvement for this data collection.

Model answers:

1. Points should be plotted with time on the x-axis and distance on the y-axis.
2. The stationary section is from 30 s to 50 s because the distance stays at 36 m.
3. Speed from 0 s to 30 s = 36 m / 30 s = 1.2 m/s.
4. Speed from 50 s to 70 s = 60 m / 20 s = 3 m/s.
5. The 50 s to 70 s section is fastest because it has the steepest line and the calculated speed is 3 m/s.
6. An improvement is to use a stopwatch carefully and repeat the journey to check reliability.

Task 2: Distance-Time Graph with Sections

Distance (m)
80 |                         D
70 |                      /
60 |                   /
50 |          B_______C
40 |        /
30 |      /
20 |    /
10 |  /
 0 +A-------------------------- Time (s)
    0    10   20   30   40

Questions:

1. Describe the motion from A to B.
2. Describe the motion from B to C.
3. Describe the motion from C to D.
4. Calculate the speed from A to B if A is 0 m at 0 s and B is 50 m at 20 s.
5. Which section has zero speed?

Model answers:

1. A to B shows the object moving away from the start at constant speed.
2. B to C shows the object stationary because the line is horizontal.
3. C to D shows the object moving away again at constant speed.
4. Speed = 50 m / 20 s = 2.5 m/s.
5. B to C has zero speed.

Task 3: Journey Comparison Table

Complete the speed column and rank the objects from slowest to fastest.

Object	Distance	Time	Speed
walking pupil	60 m	40 s
cyclist	150 m	25 s
bus	600 m	60 s
train	1200 m	30 s

Model answers:

Object	Speed
walking pupil	1.5 m/s
cyclist	6 m/s
bus	10 m/s
train	40 m/s

Rank from slowest to fastest: walking pupil, cyclist, bus, train.

Task 4: Pressure Calculation Table

Complete the missing values.

Force (N)	Area (m2)	Pressure (N/m2)
50	0.5
80	0.2
100		200
	0.4	300

Model answers:

Force (N)	Area (m2)	Pressure (N/m2)
50	0.5	100
80	0.2	400
100	0.5	200
120	0.4	300

Task 5: Pressure Investigation Results

A student places the same weighted block on soft clay using different contact areas.

Contact area (cm2)	Depth of mark (mm)
10	18
20	9
40	5
80	2

Questions:

1. Describe the pattern.
2. Explain the pattern using pressure.
3. Identify the independent and dependent variables.
4. Suggest one control variable.
5. Suggest one improvement.

Model answers:

1. As contact area increases, the depth of the mark decreases.
2. The same force is spread over a larger area, so pressure decreases and the mark is shallower.
3. Independent variable: contact area. Dependent variable: depth of mark.
4. A control variable is the weight of the block and added masses.
5. Repeat each area three times and calculate a mean.

Task 6: Fluid Pressure Dataset

Depth in water (m)	Relative pressure reading
0.5	5
1.0	10
1.5	15
2.0	19
2.5	25

Questions:

1. Describe the relationship between depth and pressure.
2. Which result may be anomalous?
3. Explain why liquid pressure increases with depth.
4. Suggest one way to improve reliability.

Model answers:

1. Pressure increases as depth increases.
2. The 2.0 m result may be anomalous because 20 would fit the pattern better than 19.
3. Deeper water has more water above it pressing down, so pressure is greater.
4. Repeat the measurements at each depth and calculate a mean.

Task 7: Floating and Sinking Table

Object or material	Mass	Volume	Density description	Observation
wooden block	80 g	120 cm3	less dense than water	floats
metal coin	20 g	3 cm3	more dense than water	sinks
sealed plastic bottle with air	30 g	500 cm3	low average density	floats
lump of modelling clay	100 g	50 cm3	more dense than water	sinks
clay shaped as a boat	100 g	larger volume with air space	lower average density	floats if shaped well

Questions:

1. Why does the wooden block float?
2. Why does the coin sink?
3. Why can the same clay float when shaped as a boat?
4. Which force acts upwards on floating objects?

Model answers:

1. It floats because it is less dense than water and upthrust can balance its weight.
2. It sinks because it is denser than water and its weight is greater than the upthrust.
3. The boat shape increases volume and can trap air, lowering average density and displacing more water.
4. Upthrust acts upwards.

Task 8: Graph Evaluation

A student draws a distance-time graph but makes these mistakes:

• the x-axis is labelled "distance"
• the y-axis is labelled "time"
• there are no units
• the scale jumps from 0 to 10 to 100
• the student says the steepest line shows the highest pressure

Questions:

1. Identify two graph labelling errors.
2. Explain why missing units are a problem.
3. Explain why the scale is unsuitable.
4. Correct the student's interpretation of the steepest line.

Model answers:

1. Time should usually be on the x-axis and distance on the y-axis.
2. Without units, readers cannot tell whether distance is in metres or kilometres, or whether time is in seconds or minutes.
3. The scale is uneven, so the plotted pattern may be misleading.
4. The steepest line shows the greatest speed, not the highest pressure.

Task 9: Reading Stimulus - Submarines

A submarine can move up and down in water by changing how much water is inside its ballast tanks. When the tanks fill with water, the submarine's mass increases while its outside volume stays nearly the same. This increases its average density, so it sinks. When compressed air forces water out of the tanks, the submarine's average density decreases. Upthrust can then be greater than its weight, so the submarine rises.

Questions:

1. What happens to the submarine's average density when ballast tanks fill with water?
2. Why does the submarine sink when more water enters the tanks?
3. What force pushes upwards on the submarine?
4. Why does the submarine rise when air pushes water out?
5. Give one reason submarines need to be strong when travelling deep underwater.

Model answers:

1. Its average density increases.
2. Its weight increases and can become greater than upthrust.
3. Upthrust pushes upwards.
4. Its average density decreases, so upthrust can be greater than weight.
5. Water pressure increases with depth, so the submarine must withstand high pressure.

Exam-Style Questions and Model Answers

Multiple-Choice Questions

1. Which equation is used to calculate speed?

A. speed = time / distance
B. speed = distance / time
C. speed = force / area
D. speed = mass / volume

Answer: B. Speed is distance travelled per unit time.

2. A horizontal line on a distance-time graph means:

A. the object is stationary
B. time has stopped
C. pressure is zero
D. the object is accelerating

Answer: A. The distance stays the same while time passes.

3. Which unit is suitable for the speed of a runner?

A. N
B. Pa
C. m/s
D. m2

Answer: C. Speed can be measured in metres per second.

4. What happens to pressure if the same force acts over a smaller area?

A. pressure decreases
B. pressure increases
C. pressure stays the same
D. pressure becomes zero

Answer: B. Pressure increases because the force is concentrated into a smaller area.

5. Which statement about balanced forces is correct?

A. Balanced forces always mean an object is stationary.
B. Balanced forces cause acceleration.
C. Balanced forces are equal and opposite, causing no change in motion.
D. Balanced forces only act in liquids.

Answer: C. Balanced forces do not change speed or direction.

6. Why does liquid pressure increase with depth?

A. deeper water has more water above pressing down
B. water disappears near the surface
C. pressure only acts upwards
D. gravity stops acting underwater

Answer: A. More water above means greater pressure.

7. A steel ship can float because:

A. steel is always less dense than water
B. heavy objects cannot sink
C. the ship has a large volume, contains air, and displaces enough water
D. upthrust only acts on large objects

Answer: C. The ship's average density and displaced water allow upthrust to balance weight.

8. Which is a non-contact force?

A. friction
B. normal reaction
C. gravity
D. water resistance

Answer: C. Gravity acts without direct contact.

Fill-in-the-Blank Questions

Use these words: speed, pressure, upthrust, area, distance, stationary, density, force

1. A push or pull is a ________.
2. ________ is how far an object travels.
3. Distance divided by time gives ________.
4. Force divided by area gives ________.
5. A horizontal line on a distance-time graph means the object is ________.
6. ________ is the upward force from a fluid.
7. Increasing contact ________ lowers pressure if the force stays the same.
8. ________ compares mass with volume.

Answers:

1. force
2. distance
3. speed
4. pressure
5. stationary
6. upthrust
7. area
8. density

Short Recall Questions

1. Define speed.

Model answer: Speed is distance travelled per unit time.

2. Define pressure.

Model answer: Pressure is force divided by area.

3. What is the unit of force?

Model answer: The unit of force is the newton, N.

4. What is the unit of pressure?

Model answer: Pressure is measured in pascals, Pa, or N/m2.

5. What is density?

Model answer: Density is mass per unit volume, or how much matter is packed into a space.

6. What is buoyancy?

Model answer: Buoyancy is the floating effect caused by upthrust from a fluid.

Calculation Questions

1. A pupil walks 90 m in 60 s. Calculate the speed.

Model answer:

speed = distance / time
speed = 90 m / 60 s
speed = 1.5 m/s

2. A cyclist travels at 5 m/s for 40 s. Calculate the distance.

Model answer:

distance = speed x time
distance = 5 m/s x 40 s
distance = 200 m

3. A trolley travels 30 m at 3 m/s. Calculate the time taken.

Model answer:

time = distance / speed
time = 30 m / 3 m/s
time = 10 s

4. A force of 120 N acts over an area of 0.6 m2. Calculate the pressure.

Model answer:

pressure = force / area
pressure = 120 N / 0.6 m2
pressure = 200 N/m2

5. A boot presses on the ground with a force of 600 N. The sole area is 0.03 m2. Calculate the pressure.

Model answer:

pressure = 600 N / 0.03 m2
pressure = 20000 N/m2

Diagram Questions

1. Label the forces on the box.

              ?
              ^
              |
        [ box on table ]
              |
              v
              ?

Model answer: The upward force is normal reaction. The downward force is weight.

2. Explain what happens if the downward weight equals the upward normal reaction.

Model answer: The forces are balanced, so there is no change in vertical motion. The box remains stationary on the table.

3. In this diagram, which direction will the trolley accelerate?

Friction 10 N <---- [ trolley ] ----> Pulling force 30 N

Model answer: It accelerates to the right because the pulling force is larger than friction, giving an unbalanced force to the right.

4. Explain the pressure difference shown.

Same force down        Same force down
      v                      v
    [__]                  [________]
 small area              large area
 high pressure           lower pressure

Model answer: The same force gives higher pressure on the smaller area because pressure equals force divided by area. The large area spreads the force out and lowers the pressure.

Practical Method and Variables Question

A student investigates how ramp height affects the speed of a trolley.

1. Identify the independent variable.
2. Identify the dependent variable.
3. Give two control variables.
4. Explain why repeats are useful.
5. Suggest one improvement to increase accuracy.

Model answer:

1. The independent variable is the height of the ramp.
2. The dependent variable is the speed of the trolley, found from distance and time.
3. Control variables include the same trolley, same ramp surface, same distance measured, and same release method.
4. Repeats help check whether the results are reliable and help identify anomalies.
5. Use light gates or a carefully positioned timing system to reduce reaction time error.

Longer 6-8 Mark Question 1

Explain why a steel ship can float but a steel nail sinks. Use density, volume, displaced water, weight, and upthrust in your answer.

Model answer:

A steel nail sinks because it has a small volume and high density. It only displaces a small amount of water, so the upthrust acting upwards is small. Its weight is greater than the upthrust, so it sinks.

A steel ship is made from steel, but it is not a solid block of steel. It has a large hollow shape and contains air. This gives it a much larger volume and lowers its average density. The ship displaces a large amount of water. The displaced water produces a large upthrust. When the upthrust balances the ship's weight, the ship floats. This shows that floating does not depend only on weight; average density, volume, displaced water, weight, and upthrust all matter.

Longer 6-8 Mark Question 2

A student investigates how contact area affects pressure. Describe a fair method, identify variables, explain the expected results, and suggest improvements.

Model answer:

The student could place a rectangular block on soft clay using different faces of the block. The independent variable is the contact area of the block. The dependent variable is the depth of the mark in the clay. Control variables include the same block, the same added mass, the same soft surface, and the same time left on the clay.

The student should place the block on one face, leave it for 10 seconds, remove it, and measure the depth of the mark with a ruler. They should repeat this three times for each contact area and calculate a mean. They should then turn the block onto a different face and repeat the method.

The expected result is that smaller contact areas make deeper marks because the same force is spread over a smaller area, producing higher pressure. Larger contact areas should make shallower marks because the force is spread out and pressure is lower.

Improvements include repeating results, smoothing the clay between tests, using the same mass each time, and measuring the mark carefully at the same point. A limitation is that clay may not return to exactly the same condition each time.

Longer 6-8 Mark Question 3

Explain how forces change during a parachute jump and link balanced and unbalanced forces to changes in speed.

Model answer:

At the start of the jump, the parachutist's weight acts downwards. Air resistance acts upwards, but it is small at first because the parachutist is moving slowly. The forces are unbalanced downwards, so the parachutist accelerates.

As the parachutist speeds up, air resistance increases. Eventually air resistance can equal weight. The forces are then balanced, so the parachutist continues falling at a constant speed.

When the parachute opens, the surface area increases greatly. This makes air resistance much larger. Air resistance is then greater than weight, so the forces are unbalanced upwards compared with the motion. The parachutist decelerates. Later, the speed becomes lower and air resistance decreases until it balances weight again. The parachutist then falls at a lower constant speed and can land more safely.

Revision Checklist

Use this checklist before a quiz or test.

Motion, Distance, Time, and Speed

• I can define motion as a change in position over time.
• I can define distance and choose sensible units such as m or km.
• I can define time and choose sensible units such as s, min, or h.
• I can define speed as distance travelled per unit time.
• I can use speed = distance / time.
• I can rearrange the speed equation to calculate distance or time.
• I can include correct units such as m/s or km/h.

Distance-Time Graphs

• I can label time on the x-axis and distance on the y-axis.
• I can explain a rising straight line as constant speed.
• I can explain a steeper line as greater speed.
• I can explain a horizontal line as stationary.
• I can calculate speed from a straight section of a graph.
• I know a steeper distance-time graph does not mean higher pressure.

Forces and Motion

• I can define force as a push or pull.
• I can name contact and non-contact forces.
• I can explain balanced forces as equal and opposite.
• I know balanced forces can mean stationary or constant speed.
• I can explain unbalanced forces causing acceleration, deceleration, or direction change.
• I can interpret simple force diagrams.

Pressure

• I can define pressure as force divided by area.
• I can use pressure = force / area.
• I can use units Pa and N/m2.
• I can explain why smaller area gives higher pressure for the same force.
• I can apply pressure ideas to pins, knives, skis, shoes, tyres, and bag straps.

Fluids

• I know liquids and gases are fluids.
• I know fluid pressure acts in all directions.
• I can explain why liquid pressure increases with depth.
• I can use examples such as dams, ears underwater, balloons, tyres, and air beds.

Density, Upthrust, and Buoyancy

• I can define density as mass per unit volume.
• I can explain that density is not the same as weight.
• I can define upthrust as the upward force from a fluid.
• I can explain floating as upthrust balancing weight.
• I can explain sinking as weight being greater than upthrust.
• I can explain why heavier objects do not always sink.
• I can explain why a steel ship floats but a steel nail sinks.

Practical Skills

• I can identify independent, dependent, and control variables.
• I can describe a fair test for motion or pressure.
• I can explain repeatability and reliability.
• I can identify anomalies in data.
• I can suggest improvements to accuracy and precision.
• I can use evidence from tables, graphs, and diagrams in explanations.