8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Year 7 Recall Starter Questions

Answer the recall questions on page 95

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1. A push or a pull (a force is an interaction which can change the motion of an object ).
2. The object will move in the direction of the bigger force.
3. As arrows.
4. Stationary or at rest.
5. Acceleration.
6. Constant speed.

Types of force

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Equipment order

Tuesday p5

18/06/24

SS 18 8E3 19

7P1.1 Forces circus

Balloon (inflated)

Trolley with hooks at both ends

2 long pieces of string

Mass hangers - small 2 large both full

2 pulley wheels

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100N

20N

20N

40N

Which direction will this ball move in?

How do you know?

On whiteboards

Can you work out how big the force is?

• What you have just done in your head is to calculate the resultant force acting on the ball.
• The resultant force is the overall force acting on something.
• Objects always accelerate in the direction of the resultant force, which we’ll talk about in detail in another lesson.
• Today we’re going to practice calculating the size of the resultant force.

What is the size of the resultant force?

10N

30N

Resultant Force

40N

What is the size of the resultant force?

10N

6N

16N

Resultant Force

What is the size of the resultant force?

2N

3N

Resultant Force

7N

2N

Question 4

• Now try questions 1 to 10 to practice this.
• Remember to draw an arrow to show which direction the resultant force is in.

What is the size of the resultant force?

10N

30N

Resultant Force

20N

What is the size of the resultant force?

10N

6N

4N

Resultant Force

• Now try questions 11 to 20 to practice this.
• Remember to always draw an arrow to show which direction the resultant force is in.

2N

3N

Resultant Force

1N

2N

What is the size of the resultant force?

What is the size of the resultant force?

20N

4N

10N

Resultant Force

6N

• Now try questions 21 to 30 on the worksheet to practice this.
• There are some extension questions to try if you get all those done.

What is the size and direction of the resultant force?

2N

4N

Resultant Force

6N

What is the size and direction of the resultant force?

6N

4N

10N

Resultant Force

What is the size and direction of the resultant force?

1N

3N

Resultant Force

5N

1N

What is the size and direction of the resultant force?

1N

3N

Resultant Force

2N

What is the size and direction of the resultant force?

8N

6N

2N

Resultant Force

What is the size and direction of the resultant force?

3N

7N

Resultant Force

1N

3N

What is the size and direction of the resultant force?

10N

2N

4N

Resultant Force

4N

Calculate the resultant force in each example and write the answer and the direction of the resultant force.

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

5 quick questions

Answer the questions on page 102

Frictional forces

• Whenever an object moves against another object, it feels frictional forces.
• These forces act in the opposite direction to the movement.

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Frictional forces

• Friction makes it more difficult for things to move.
• Friction always tries to slow moving objects down. We say it opposes motion.
• Friction is created whenever two touching objects or surfaces move past each other.
• There is a maximum value for the frictional force which depends on:
• the force pushing the two surfaces together;
• the state of the surfaces in contact.

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Frictional forces

• Friction also occurs when things move through air. This is called air resistance or drag.

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Why does this make your hands warm?

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On a microscopic level, your hands have very bumpy surfaces. When these are rubbed over each other, there is a lot of frictional force created, which transfers kinetic energy to thermal energy.

Investigate friction by comparing the amount of force needed to move an object on different surfaces

Variables: Key Terms

• Independent variable = what we change in our investigation

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• Dependent variable = what we measure for each change of the independent variable

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• Control variables = what we keep the same

Investigate friction by comparing the amount of force needed to move an object on different surfaces

Can you identify the different variables in this experiment?

Page 102

8E3

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Got to here

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Tuesday 25^th June

5 quick questions

Answer the questions on page 102

• Set up the equipment by attaching a newton metre to a 600 g mass.
• Place your first surface type on the table or bench.
• Pull the mass for a set distance across the surface at a constant speed. Measure the reading on the newton meter.
• Return the mass back to the starting position and repeat a further 2 times.
• Calculate a mean force.
• Swap the surface type and repeat steps 3, 4 and 5.

Graphs

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The perfect graph

Conclusion �

Which surface applied the most friction? Include data to show this.

Which surface applied the most friction? Include data to show this

How would you describe the surface of the material that applied the most friction compare to one that applied the least?

Key idea

Who is correct?

Apply your learning

True or False?

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• Friction slows things down   
• True (but not always)            
• Cars need friction to keep moving
• true
• Cars need friction to stop
• true
• You could not walk without friction
• true
• Friction is useful to gymnasts
• true
• Matches light because of friction
• true
• Shoelaces stay tied up because of friction
• true
• You could not pick up a cup of tea without friction
• true
• Snow increases the friction between your shoes and the ground
• false
• Pencils do not need friction to write
• false

Applying understanding

Where are the frictional forces in these scenarios?

Are they useful?

What could you do to increase or decrease them?

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

5 quick questions

Answer the questions on page 108

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8P1.2 Pressure between solid surface.

1. How can you increase the pressure on a the surface of an object?

Increase the force or reduce the area the force acts on

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2. What are the units for area?

  m²

3. What are the units for force?

 N Newtons

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4. Why does a knife cut you but a spoon doesn’t?

 Very small surface area

5. Why is it easier to float in salty water compared to fresh water?

 Salty water has a higher density than fresh water

Pressure between solid surfaces

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Which is creating the most pressure on the ground?

Which is exerting a greater force on the ground?

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A force can be a push or a pull.

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When a force is exerted on an object it can change the object's speed, direction of movement or shape.

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Pressure is a measure of how much force is acting upon an area.

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Pressure can be found using the equation pressure = force ÷ area.

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 Therefore, a force acting over a smaller area will create more pressure.

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Using low pressure

A force spread over a large area means low pressure, e.g. skis and snowboards.

The large surface area of the board means the skier exerts very little pressure on the snow.

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This means he slides over the top of the snow and does not sink into it.

Using high pressure

A force concentrated on a small area means high pressure, e.g. high heeled shoes, needles, ice skates, sharp knives.

The narrow blade of a knife means that it exerts a high pressure and makes it easier to cut fruit and vegetables.

The high pressure of the blade of an ice-skate melts the ice and helps the skater slide across the surface.

Analysing a practical : What affects pressure?

Equipment – Plasticine, dowels of different areas (cm2), masses (weight = force, N).

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Method

• Using the plasticine you will be seeing how the different size dowels and different size force make different sized impressions in the plasticine.
• Knead the plasticine until it becomes soft and easily shaped. Make it into a regular shape with some depth
• Place a dowel onto the plasticine and rest the mass on top (do not push down).
• Remove the dowel and mass and observe the depression in the plasticine. Record what you observe.
• Repeat step 1- 4 changing to a different sized dowel and repeat the experiment
• Repeat step 1-4 with the same sized dowel but different masses.

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• Conclusion
• As the size of dowel increased, I observed….

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• As the size of the force increased, I observed….

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• This tells me …

deeper shallower plasticine indentation higher lower force area pressure

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Calculating pressure

Pressure is the force per unit area and is calculated using this formula:

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Pressure is measured in:�Newtons per square metre (N/m²), which are also called pascals (Pa).

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Pressure can also be measured in:�Newtons per square millimetre (N/mm²);�Newtons per square centimetre (N/cm²).

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F newtons N

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P newtons per Pascals N/m²

kilogram Pa

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A metres squared m²

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10. A force of 20 N acts over an area of 4 m². Calculate the pressure it exerts.

10. A force of 4 N acts over an area of 2 m². Calculate the pressure it exerts.

Answer questions 12 – 17 on page 111.

Answer questions 18 – 23 on page 112.

Why do camels have large feet?

The large surface area of the feet reduces the pressure on the sand, so the camel does not sink.

Why do footballers have studs on their boots?

The small surface area of the studs increases the pressure on the grass, so the boots sink in a little giving the boots grip.

Why shold you never hold a parcel by the string?

The small surface area of the string increases the pressure on the hand, so the string cuts into your hand.

Why do tractors have such wide tyres?

The large surface area of the tyres reduces the pressure on the snow or mud, so the tractor does not sink.

Why should stilettos never be worn on a polished wooden floor ?

… or to prom?

The small surface area of the heel increases the pressure on the wood, so the heels sink into the wood.

Why are skis so long?

The large surface area of the skis reduces the pressure on the snow, so the skier does not sink.

8E3

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Got to here

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Thursday 27^th June

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Why do camels have such large feet?

They spread their weight over a larger area

They help them grip the sand

They make them quicker

Click again for answer

Y

M

C

A

B

C

They help them attract mates

D

Why does Mr Claxton not let you wear football boots in the sports hall

They are too dirty

The studs increase the pressure and would make holes in the floor

They don’t match the decor

Click again for answer

Y

M

C

A

B

C

They make too much noise

D

3 quick questions and key ideas

What do you think?

Pressure in Fluids

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In physics, a fluid is a substance that continually deforms (changes shape / flows) under an external force. Fluids are a state of matter and include liquids, gases and plasmas.

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Bumping particles

The particles in a gas move quickly in all directions, but they don't get far before they bump into each other or the walls of their container.

When gas particles hit the walls of their container they exert a force called gas pressure. The more particles that collide with (hit) the walls, the higher the pressure.

This is why the pressure in a tyre or balloon goes up when more air is pumped in.

Pressure in a fluid

A fluid can be used to transmit pressure from one place to another.

Hydraulics demo

• Pressure is the amount of force acting on a certain area.

pressure = force ÷ area

• Pressure in a fluid is caused by the force of particles hitting a surface

8P1.3 Pressure in Fluids

Magic glass

Coke can demo

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

5 quick questions

https://www.youtube.com/watch?v=IhLewdpF2fI

8P1.4 Pressure and depth

What is the ‘deepest’ layer of the atmosphere.

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What is the total depth of the atmosphere?

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How much deeper is the troposphere than the mesosphere?

8P1.4 Pressure and depth

Troposphere

400km

8P1.4 Pressure and depth

Atmospheric pressure changes with altitude. The higher you go:

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• the lower the weight of the air above you
• the lower the atmospheric pressure

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For example, atmospheric pressure at sea level

is about 100,000 Pa, but it is only about

21,000 Pa at the cruising height of an airliner.

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Why is this?

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The higher you go above the Earth, there is less

atmospheric gas above you applying pressure

on you.

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21,000 Pa

100,000 Pa

Answer the questions on page 117

Pressure in a liquid

Pressure in a liquid:

• acts in all directions;
• increases with depth.

A liquid can be used to transmit pressure from one place to another.

Pressure in a liquid

high pressure

low pressure

The relationship between pressure and depth is shown by a water bottle with holes along its length.

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Just like the atmosphere, liquids exert pressure on objects. The pressure in liquids changes with depth. The deeper you go:

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• the greater the weight of liquid above
• the greater the liquid pressure

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Remember, the pressure is acting in all directions.

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Pressure in a liquid

Application

9. These three diving pools each have the same depth of water.  At the bottom of 

which pool is pressure the greatest?

Answer the questions on page 118

Task:

Task:

Graphs: SPLAT

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Answer the questions on page 118

Let’s do this together and then have a go at question 13 on your own.

Multiple Choice

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Objects A, B & C have just been put into water. �Name the two forces acting on the objects. �What is going to happen to objects A, B & C?

A

WEIGHT

UPTHRUST

Draw a free body diagram showing the resultant force on each of these objects in air and describe what is happening to each.

A

50 N

20 N

20 N

20 N

20 N

50 N

A

30 N UP

30 N DOWN

0 N

FLOATING

GOING UP

SINKING

Liquid pressure is exerted on the surface of an object in a liquid.

This pressure causes upthrust.

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An object placed in a liquid will begin to sink.

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As it sinks, the liquid pressure on it increases

and so the upthrust increases.

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Will the object float or sink?

• If the weight is greater than the upthrust?

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• If the upthrust is greater than the weight?

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Floating and Sinking

It will sink.

It will float.

For a floating object, the upthrust is equal (or greater) and opposite to the object’s weight.

An object will continue to sink if its weight is greater than the maximum upthrust.

Object can float in fluids. This includes both liquids and gases

Objects sink if the force pushing down is greater than the forces pushing up

Another way of saying this is that the resultant force acts downwards

Objects float if there is no resultant force.

resultant, up, down, downwards, liquids, fluids, gases

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Icebergs

Why do some objects float and some sink?�

• For a floating object, the upthrust is equal and opposite to the object’s weight.
• An object will continue to sink if its weight is greater than the maximum upthrust

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Complete the questions on page xx

Density

Block float

All of these blocks have the same mass.

They all float in water.

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Block float

All the blocks are floating in water.

What do you think about these statements?

Water has a density of 1g/cm³.

Objects with a density ______________ than 1g/cm³ sink.

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Objects with a density ________________ than 1g/cm³ float.

Dancing raisins

Have you ever seen dancing raisins? ?

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No, more like this:

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So, can you explain how it works?

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10. What happened when the raisins were dropped into the fizzy drink?

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11. After a while, what became attached to the raisins?

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12. What is the reason why the raisins rose to the top of the container?

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13. What happened when the raisins got to the top?

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14. What is the name of the gas that was created in this experiment?

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15. Would the same thing happen if we put the raisins in water? Why?

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Y7 Core Knowledge Questions

1. Name 8 forces

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• State the unit for force

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• What is the motion of a car if all the forces are balanced?

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• If force A is 10N and force C is 10N, what is the resultant force on this object?

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• What two things do the arrows on a force diagram demonstrate?

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• If D is thrust, describe the motion of the object.

Thrust, air resistance, friction, weight, reaction, upthrust, lift, magnetism

Newton, N

Stationary or constant speed

0 N

Size of force & Direction of force

It is travelling at a constant speed in a straight line

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Balanced or unbalanced?

A B

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C

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D E

Calculating resultant force

Which has the biggest resultant force?

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How would you explain your answer?

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Tug of war B

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There is the biggest difference between the two forces between Carl and David .

Balanced or unbalanced?

Describe the motion of the object:

• is it stationary, accelerating, decelerating or moving at a constant speed?
• is it moving up, down, left, right?

Accelerating down

Balanced or unbalanced?

Describe the motion of the object

Decelerating but still moving to the left

Balanced or unbalanced?

Describe the motion of the object

stationary

Balanced or unbalanced?

Describe the motion of the object

Accelerating to the right at a constant altitude.

Apples and balloons

• Hold a mass in your hand – this is a Newton (its about the same weight as an apple)
• Look at the apple in the tree (a clamp stand).
• If there is a downwards force on the apple, why isn’t it falling?
• What happens to the forces as the apple starts to fall from the tree?
• Look at the apple on the desk
• If there is a downwards force, why isn’t it falling through the table?
• Squeeze a balloon (check for latex allergies) but keep it still
• Make the same shape against the desk.

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Balanced and unbalanced forces – summary

• and the object is stationary, it will remain stationary

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• and the object is moving, it will continue to move at the same speed and in a straight line.

If the forces are unbalanced, two things can happen:

If the forces on an object are balanced:

In other words, the object will continue to do what it is already doing without any change.

• The speed can change. This is called acceleration.

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• The direction of motion can change.

Answer question 1 on page 129 – the question describes the staring position and then something changes. Describe what happens after the change.

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Then answer questions 2 - 6 on pages 130 – 131.

Apples and balloons

• Hold a mass in your hand – this is a Newton (its about the same weight as an apple)
• Look at the apple in the tree (a clamp stand).
• If there is a downwards force on the apple, why isn’t it falling?
• What happens to the forces as the apple starts to fall from the tree?
• Look at the apple on the desk
• If there is a downwards force, why isn’t it falling through the table?
• Squeeze a balloon (check for latex allergies) but keep it still
• Make the same shape against the desk.

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Newton’s first law of motion

If the forces acting on an object are balanced, it will stay stationary.

Or if its already moving, it will keep moving at the same speed in the same direction.

Complete the gap fills on 131, then answer the questions on 132

there

direction

force

stay at rest speed continue to move

• Who is moving the fastest?
• Who is not moving at all?
• Bev will continue to move at 7 m/s. How can you tell this from the drawing?
• What will happen to Al’s speed? Explain your answer.
• What will happen to Charlie’s speed? Explain your answer.
• What will happen to Dinesh’s speed? Explain your answer.
• What will happen to Ellie’s speed? Explain your answer.
• What is causing the forces in the drawing that are slowing the cyclists down?

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Answer the questions on page 133 - 1345

8P1

Forces and motion

Equations, units and key words

Concept 0 Year 7 Review

Concept 1 Resultant force

Concept 2 Friction

Concept 3 Pressure between solid surfaces

Concept 4 Pressure in fluids

Concept 5 Pressure changes with height and depth

Concept 6 Floating and sinking

Concept 7 Newton’s First law of motion

Concept 8 Relative motion

Practical order

Box of toy cars

Relative motion

Playtime

• Draw a stick man onto a whiteboard.
• “Drive” one of your cars past the man. Think about how the car’s motion appears to the man.
• “Drive” your cars alongside each other. Imagine you were in one of the cars. How fast are you moving compared to the man and the other car?
• “Drive” your cars alongside each other, but with one faster than the other. Imagine you were in the slower car. How fast are you moving compared to the man and the other car?
• “Drive” your cars towards each other. Imagine you were in one of the cars. How fast are you moving compared to the other car?

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• Relative motion is the speed of something compared to the observer.
• If you are in a car and go past people at a bus stop, you may not see them very well because you are moving and they are still.
• If you overtake a motorbike in your car, and look at the rider, it may seem you spend longer going past them than the people at the bus stop.
• If you have travelled in a car on the motorway, you may have noticed that other cars passing by appear to move slowly past you, even though you know the actual speeds of the two cars are very high. This is because of their relative motion to each other.

Key idea

difference

motion

speed

greater

lower

direction

Work in pairs to answer the questions on pages 135 - 137

If the runner stopped what would the relative speed of the car be compared to the runner?       ��

If the car started reversing at 10 m/s what would the relative speed be between it and the runner?

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If a bike overtook the car and runner at 40 m/s what would its relative speed be to the runner? And to the car?

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25 + / - 0 = 25 m/s

10 + 3 = 13 m/s

40 – 3 = 37 m/s

40 - 25 = 15 m/s

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50 + 30 = 80 mph

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20 – 11 = 9 m/s

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100 - 70 = 30 mph

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7 – 2 = 5 m/s

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Observer B will think the runner is moving faster.

Now, have a go at the exam questions on pages138 - 141