Year 8 Science Lessons PHYSICS LESSONS Lesson 1 ......Lesson 2: Levers in Action Lesson Purpose:...

Year 8 Science Lessons PHYSICS LESSONS

Lesson 1: Levers Lesson Purpose: Describe actions of levers What is a lever? (A)

Levers are devices that are used to apply

forces more conveniently, or to transfer a

small force into a bigger force. They are

usually long, thin and stiff. Levers have a

pivot, around which they rotate. The pivot

can also be referred to as a fulcrum. The load

is the object that is trying to be moved. The

force that is applied to a lever is known as an

effort.

Comprehension questions

1. State what a lever is used for (A) 2. Using the diagram, describe the load, effort and fulcrum of a lever (A) 3. Summarise the above text in no more than 10 words (A) 4. Challenge: Suggest examples of levers (A)

What are examples of levers? (B)

Levers can be placed into three separate classes (or groups). The class of a lever depends on the

position of its pivot, effort and load.

• A class 1 lever has the load and effort on opposite sides of the pivot. An example of this

would be a crowbar. A class 1 lever has a mechanical advantage (the effort is smaller

than the load)

• A class 2 lever has the load and effort on the same side of the pivot, with the load being

closer to the pivot. An example of a class 2 lever would be a wheelbarrow. A class 2 lever

has a mechanical advantage.

• Unlike class 1 and 2 levers, class 3 levers have no mechanical advantage. The effort and

load are both on the same side of the pivot, but the effort is closer to the pivot. An

example of a class 3 lever is a pair of tweezers. Class 3 levers are good for grabbing

small, fiddly or dirty objects.


1. State the three classes that levers can be categorised as (B) 2. Describe the three different classes of levers (B) 3. Compare and contrast class 2 and class 3 levers (B) 4. Challenge: For each of the following examples, suggest a class for them, using diagrams to

explain your choices. a. Pair of scissors b. Nut cracker c. See-saw d. Barbecue tongs e. Pair of pliers

Lesson 2: Levers in Action

Lesson Purpose: Describe the operations of levers

What do levers do? (A)

Levers are known as force multipliers. They can reduce the effort needed to move a load by

increasing the distance over which it is acting. This means that only a small amount of force is

needed to move a large object. The further away the effort is from the pivot, the more the force is

multiplied. An example of this would be using a spoon to open the lid on a syrup tin.

Levers can also act as distance multipliers. This means that a smaller distance applied to one side of

the lever could be increased on the other side of the lever.


1. Describe a force multiplier (A) 2. Describe a distance multiplier (A) 3. Use diagrams to represent a force multiplier and a distance multiplier (A) 4. Challenge: Suggest situations where a distance multiplier may need to be used.

What is work done? (B)

When a force is used to move an object over a distance work is done. Examples of work done can be

seen all the time, such as lifting a box, walking up stairs or moving a lever. Whenever work is done,

energy is transferred from one place to another. Both energy and work done is measured in Joules

(J).

Work done is calculated using the following equation:

Work done (J) = Force (N) x distance (m)

W = F x d

Example: A 10 N box is lifted 2 metres. Calculate the work done.

Work done = Force x distance

Work done = 10 N x 2 m

Work done = 20 J

You need to ensure that the units are correct for the equation. Be prepared to convert cm to m

(divide by 100), mm to m (divide by 1000) and kJ to J (multiply by 1000)


1. Describe work done (B) 2. State the equation used to calculate work done (B) 3. Rearrange the equation for: (B)

a. Force b. distance

4. Complete the below calculations (challenge yourself!)

Easy Medium Hard

Write the equation to

calculate work done.

What is the work done

if we apply a 1.2N force

and we move 4 m in the

direction of force?

Thinking about energy

transfers:

When you rub your

hands together what are

the energy transfers?

Rearrange this equation

for force applied.


if we apply a 7N force

and we move 8 m in the

direction of the force?

When you boil a kettle

what energy transfers

are happening?

Rearrange this equation

for distance moved in

the direction of force.

What distance is moved

if we have a 8N force

and the work done is 90

J?

Walking up a flight of

stairs, what are the

energy transfers?

What is the unit of

force?

What is the distance

moved if we have a 70N

force and work done is 8

J?

When you roll a ball

down a hill what are the

energy transfers?

What is the unit of work

done?

What force is required

to move 7 m if the work

done is 9 J?


when a force of 5 N is

applied to a ball and it

moves 80 m?

What is the unit of

distance?


to move 19 m if the

work done is 9 J?


to a car if a force of 9

N is applied and it moves

7 km?

What work is done when

we apply a force of 5N

and move in the

direction of the force 2

m?


to move 7 m if the work

done is 21 J?


to a person if a force of

1.3N is applied and the

person moves 6m?

Lesson 3: Turning Effect Lesson Purpose: To calculate the turning effect of a lever

What is a ‘moment’? (A)

Levers are used to make work easier, they rely on the physics principle of ‘moments’ to make this

work. In science (physics) ‘a moment’ is the turning effect of a force – a turning motion caused by a

force being applied to an object (Think of your hand applying a force on a door handle and it

turning). Moments are measured in the units Newton metres,

which is written as Nm. They are calculated by multiplying the

force in Newtons (N) applied to a lever by the distance in metres

(m) from the force to the pivot (the point about which the lever

is turning).

Depending on the direction of the force, a moment can turn

either clockwise or anticlockwise.


1. Why are levers used? (A) 2. State what a moment is (A) 3. What unit are moments measured in? (A) 4. Write the equation for calculating a moment. (A) 5. Convert 10 metres into km, cm, mm and um.

Calculating moments (B)

Moments are calculated to work out how much force will be needed to lift a given load. If a load is

particularly heavy, engineers can adjust the length of the lever to make the moment greater, making

the load easier to lift.

The formula triangle to the left can be used to calculate the

moment of the lever below:

6 Newtons x 2 metres = 12 Nm

Comprehension Questions

1. Calculate the moment of this force. Moment =

2.Calculate the moment of this force. Moment =

pivot 3 Newtons

1.5 metres

3. Calculate the length of this lever if the moment is 8 Nm

Length =

pivot 2 Newtons

?? metres



6. Calculate the moment of this force

Using the principle of moments, calculate whether the seesaws below are balanced or unbalanced. Show your working out.

6.

7.

8.

Balanced or unbalanced? Balanced or unbalanced? Balanced or unbalanced?

All of the seesaws below are balanced. Fill in the missing number using the principle of moments. Show your working out.

pivot 3 Newtons

12 metres

10kg 5kg

1m 2m

4.10kg 15kg

12m 8m

5.20kg 15kg

8m 11m

6.

pivot 6 Newtons

2 metres

7kg ??kg

10m 5m

9.??kg 15kg

15m 3m

10.

28kg12kg

??m140m

11.

Challenge: Calculate the weight (in N) of child W if the seesaw is balanced. Ext – Convert the weight in Kg

Lesson 3: Machines

Lesson Purpose: To apply the principle of moments to machines

What is a machine? (A)

The scientific definition of a machine is an object that is used to make work easier to do. Remember, in science ‘work’ is described as transferring energy to an object when a force is applied to it over a distance. Therefore a machine is simply an object that makes it easier to do something involving forces. Levers are one of the simplest machines used by humans. Simple machines may have very few or no moving parts and lead to a change in the magnitude (size) of a force, such as a lever (we call these force multipliers) or may change the direction of a force, such as a pulley. Other simple machines include a wheel and axle, a wedge, a pulley, a screw and an inclined plane (ramp). Comprehension questions

1. Define the term ‘machine’ (A) 2. Describe two ways a machine may affect a force? (A) 3. The image below shows the six different types of simple machine, use the information in

paragraph A to label each one. (A)

Challenge - Explain how a lever affects the forces applied to it Manipulating forces (B)

As mentioned previously, machines may manipulate the magnitude (size) of a force or the direction of a force.

• Manipulating direction: A screw is a simple machine as it manipulates the direction of the force applied to it. When using a screwdriver you rotate your wrist, the screw turns, but the overall motion of the screw is to move down into the object it is pressing against. A pulley is

a small metal wheel with a cord or rope threaded over it, it too can manipulate the direction a force is travelling in. When a rope attached to a pulley is pulled downwards a load attached to the other end is lifted upwards. Many modern day lifts and elevators work using this simple principle.

• Manipulating magnitude: The front two wheels on a car are attached together by a metal bar called an axle. The cars engine turns the axle, which is turn causes the cars wheel to rotate. This is an example of a force multiplier. The car engine turns the axle in a small circle, this causes the wheels to turn in a large circular motion. This is an efficient way of using a small amount of energy to apply a large force to an object.

• Simple machines can be used to decrease (as well as increase) the magnitude of forces. An inclined plane (also know as a ramp) can be used to slow down objects that are moving, therefore reducing the magnitude of the force they are moving with E.g. Speed bumps.


1. State two simple machines that affect the magnitude of a force.

2. State two simple machines that affect the direction of a force. 3. State the common name of an ‘inclined plane’. 4. Explain how a pulley affects a force 5. A decorator wishes to raise a bucket of paint closer to the

ceiling. Name the simple machine he has designed and explain how it manipulates either the magnitude or size of the force

applied to the cord. 6. Large, heavy trucks driving down steep hills often find it difficult to stop at the bottom of the hill if there is traffic. To avoid accidents, local councils in Australia have installed ‘Runaway Truck Ramps’. Describe what type of simple machine this is and explain how it will affect the forces acting on the trucks.

P2 Lesson 5: Pressure Lesson Purpose: Describe what pressure is, and explain how to increase or decrease it. What is pressure? (A)

If you tried to poke a hole in something- a balloon for example- with a blunt object such as your

finger, you would need to apply a certain amount of force. Compare this to a pointier object, such as

a needle: much less force would be needed to pop the balloon. This is the result of pressure- which

is closely related to “pushing” forces. In this case, pressure was varied by changing the shape of the

object applying force on the balloon. This idea can be applied to many objects and tools, such as

knives, pins, needles (which increase pressure), or skis, thimbles and even bullet proof vests (which

decrease pressure).

The tools that increase pressure all have something in common; they work best if they are pointy or

sharp. A blunt knife will not easily cut through something and you will have to push much harder on

a blunt pin to push it into a cork board. In other words, these objects work best if they have a small

surface area.

Conversely, a camel’s foot has a broad, flat base, which gives it a large surface area. This is to help

stop the heavy camel sinking into the sand as it walks. This is an example of decreasing pressure, as

the camel’s weight is spread out over a large surface area on the sand, reducing the pressure on the

sand per cm2.

We can define pressure as “force exerted over an area”. High pressure means the force on a certain

area is large, and low pressure means the force on an area is small.

Comprehension questions 1

1. What is pressure defined as? 2. What are the two factors which can affect pressure? 3. Describe what must be changed in order to cut through butter with a blunt knife,

compared to a sharp one. 4. Explain why a camel can walk much more easily in sand than a person in high heels. 5. Challenge: A person fishing has been stranded on a frozen lake. Suggest how they might

stop themselves from falling through the ice into the freezing water. Pressure, force, and area (B)

The relationship between pressure, force and area can be shown in the following equation:

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =𝐹𝑜𝑟𝑐𝑒

𝐴𝑟𝑒𝑎 or 𝑃 =

𝐹

𝐴

This equation shows us how pressure can be increased or decreased. If the force applied is

increased, the pressure will be increased. If the force applied is decreased, the pressure is

decreased. However, if the area is increased, pressure will decrease. If the area is decreased, the

pressure will increase.

The diagram illustrates this relationship. If the area is

increased, the force will be spread out over a larger

area, which decreases pressure (even though the

overall force is the same). On the other hand, making

the area smaller means that all that force is being

applied to a smaller area. This results in increased

pressure. This effect can be felt easily by pushing one

finger into the palm of your other hand (low area, high

pressure). Next, apply the same force, but with 2 or more fingers - this increases area, reducing

pressure.

Comprehension questions 2 1) Describe what happens to pressure when:

a) Force is changed b) Area is changed

2) In order to pin a poster on a corkboard, the amount of force being applied to a blunt drawing pin is doubled. What happens to the pressure of the pin on the board?

3) The pin is still too blunt to be useful. It is sharpened so that its surface area is halved. What happens to the pressure?

4) Challenge: Suggest why it is a bad idea to swing on your chair legs so that not all four legs are on the floor (aside from the risk of falling off the chair!). Use a diagram to illustrate your answer.

5) Challenge: Use a labelled diagram to illustrate how pressure, forces and surface area affect an everyday example.

Lesson 6: Calculating pressure

Lesson Purpose: To calculate the amount of pressure acting on a surface. What are the units involved in calculating pressure? (A)

Pressure is force exerted over an area. Force is measured in Newtons (N) and area (also called

surface area) is measured in metres squared (m2). The formula for calculating pressure gives us a

clue about the units for pressure:

𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =𝐹𝑜𝑟𝑐𝑒

𝐴𝑟𝑒𝑎

Force (N) is divided by area (m2), so pressure can be measured in N/m2 (Newtons per meter

squared). We can also use the unit Pascal (Pa), which is the equivalent to N/m2 (1 Pa = 1 N/m2).

Calculating pressure simply involves dividing the force applied by the area to which it is being

applied. This can be visualised using a diagram:

If 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 =𝐹𝑜𝑟𝑐𝑒

𝐴𝑟𝑒𝑎

Then 𝑃 =10𝑁

5𝑚2

So 𝑃 = 2 𝑃𝑎.

In other words, the pressure on this surface is ‘2

Newtons per metre squared’. Remember, Pascals (Pa)

are the same as Newtons per meter squared, so it is

simpler to say the pressure on this surface is simply ‘2

Pascals’.

Comprehension questions A

1. State the units involved in calculating pressure. (A) 2. Describe what is meant by N/m2. (A) 3. What is the relationship between Pascals and Newtons per meter squared? (A) 4. Explain what happens to pressure as:

a. Force acting on a surface increases. (A) b. Force acting on a surface decreases. (A) c. The area acted upon by a force increases. (A) d. The area acted upon by a force decreases. (A)

5. Challenge: explain how the pressure exerted upon two surfaces can be the same without having the same force applied to them.

10N 5m2

How can force and area be calculated? (B)

If the pressure is known along with either force or area, the

missing information can be calculated by rearranging the

equation for pressure. To calculate force, multiply pressure

by area. To calculate area, divide force by pressure. This

relationship can be seen in a formula triangle where:

F = force

p = pressure

A = area.

Sometimes the area of a surface is not known, but the length and height are. Simply multiply the

height by the length of a surface to calculate the area of a rectangular face (or use πr2 for a circular

surface).

Remember that area is measured in m2. If the area is given in another unit, such as cm2, you may

have to convert this to m2. There are 100cm in 1m, but there are 10,000cm2 in 1m2!

Comprehension questions B

1. Write the equations to calculate pressure, force, and area, using the symbols above. (B) 2. Describe how to calculate pressure, force and area. 3. Calculate the area (in m2) of a surface with:

a. Height of 7m and length of 22m. b. Height of 10cm and length of 55cm.

4. A mechanical digger on a construction site has a weight of 46 000 N and its tracks have an area of 2.0 m2. What is the pressure of the digger acting on the ground?

5. A block of concrete has a mass of 10 000 N. The area of the block in contact with the floor is 0.8 m2. What is the pressure acting on the floor due to the block?

6. A student pushed on a door with a force of 40 N. The student estimates that the area of one side of their hand is 0.02 m2. What is the pressure acting on the door?

7. A student has a weight of 500 N and stands on the floor with a total area of contact of 500 cm2

a. What is the area in contact with the floor in square metres? b. What is the pressure acting on the floor? c. What is the pressure the floor exerts on the student?

8. This brick has a weight of 15 N.

Find the pressure it will cause on the table if:

a. The brick is resting on side A.

b. The brick is resting on side B.

c. The brick is resting on side C.

A B

C

10cm

Lesson 7: Atmospheric Pressure

Atmospheric Pressure (Pressure in gases) (A) Atmospheric pressure is the force of the weight of the atmosphere pushing down on every object on Earth. It is pressing down on your right now, but as you have felt it since birth you no longer notice it. We measure pressure using a unit called Pascals. The pressure of the atmosphere is approximately 100,000 Pascals (1 Pascal is equal to 1 N/m2). The atoms in gases are free to move and when they move around they bump into other materials like the walls in a room. The faster these gas particles are moving the more pressure they exert (as they are bumping into other materials more often). When temperature increases pressure increases and when temperature decreases, pressure decreases. When there are lots of particles in a particular volume, pressure is high however when there are a low number of atoms in a particular volume, pressure is low. Comprehension Questions (A)

1. What units are used to measure pressure? (A)

2. How would high and low temperature affect the pressure of gas? (A)

3. What is atmospheric pressure? (A)

4. How could you increase the pressure inside an air balloon? (A)

5. Challenge: Explain why the pressure in the cylinder labelled (b) is higher than the

pressure in the tube labelled (a).

Pressure and Altitude (B) The atmosphere is made up of all the gas that surrounds the Earth. Whilst we are on the ground all the air above us is pushing down on us. If there is lots of air above a person the pressure exerted on that person will be high. At higher altitudes, which means at greater distances off the ground, pressure decreases. This is because at high altitudes less air is above any given object therefore the pressure exerted by the air is less. The weight of air pushing down on a person, or any given object, decreases as altitude increases. We know that the atmospheric pressure at ground level is around 100,000 Pascals however at higher altitudes, such as the cruising level for an aeroplane, the pressure is 21,000 Pascals. Comprehension questions (B)

1. A student squashes a balloon. Describe and explain;

a) The change in the volume of the gas in the balloon. b) The change in the pressure of the balloon as the student squashes it.

2. A student collects some gas in a balloon. The student wants to increase the pressure

of the gas he has collected. Suggest 3 ways in which the student could increase gas

pressure.

3. A formula 1 car drives around a course. Whiles driving the wheels experience lots of

friction, and the temperature of the wheels increases. Explain the change in pressure

of the air in the wheels

4. Explain why a skydiver experiences less atmospheric pressure than someone at

ground level.

5. Calculate the difference in atmospheric pressure between Mount Everest and sea

level (See diagram below)

6. Challenge: Using what you know about the how atmospheric pressure changes with

altitude, suggest a reason for the difference in pressure between sea level (surface

of the sea) and the sea bed (the ground at the bottom of the sea).

Lesson 10: Pressure in Liquids Lesson Purpose: Describe pressure in liquids Pressure in Liquids (A) Liquids and gases are both called fluids because their particles can flow (move around). An object placed in a liquid experiences pressure from all areas in contact with the liquid. Upthrust is the force acting in the opposite direction to the weight of the object. This allows the object to float. However, if the weight of the object is greater than the force of the upthrust the object would eventually sink. For an object to float, the weight of

the object must balance at some point with the upthrust from the liquid. The pressure in liquids increases with depth; this means that the deeper an object is immersed (to dip) into a liquid, the greater the pressure exerted on it. Imagine a submarine surrounded by water, the pressure on the bottom of the submarine would be greater than the pressure on top. Another example is the force of water coming out from a bucket with small holes all over the sides. The holes nearer the bottom would come out with a greater force (jets) than those at the top because pressure increases with depth. Pressure in liquids is similar to how pressure is experienced in gases, as it increases with depth in liquid, but increase with height in air. Comprehension questions

1. Describe why liquids and gases are both called fluids 2. Describe the meaning of the term ‘upthrust’? 3. Explain, in terms of forces, how objects float 4. Describe how pressure on a submarine changes when under water 5. Describe the similarity between pressure in liquid and in gases Challenge: Suggest why deep sea divers need special suits and equipment to survive when they are deep beneath the sea.

Causes of pressure in liquids Pressure in liquids is caused by the particles of the liquid moving around and colliding with each other. This happens when the weight of an object is placed on (e.g. a boat), or a force is applied to the liquid (in a syringe). Another cause of pressure in liquids is gravity. The weight of an object is the pull of gravity on it. When an object is submerged in a liquid, the weight of the liquid above it becomes the pressure of the liquid on the object. Decompression sickness is when bubbles are formed in the blood of sea divers when exposed to great changes in pressure, commonly known as diver’s disease or ‘the bends’. If a diver goes deep underwater, their blood is exposed to high amounts of pressure, if they rise up in the water too quickly the pressure is relieved quickly and lots of gas bubbles escape from their blood (Think: What happens to the gas in a fizzy drink when you open the bottle and release the pressure very quickly? The pressure in the bottle is what keeps the gases in your drink) this can lead to severe problems in the body and even death. This is the reason why deep sea divers require special suits and equipment for diving. Comprehension questions

1. State two causes of pressure in liquids 2. Describe how gravity causes pressure in liquids. 3. Describe what causes decompression sickness 4. Explain what happens in the body tissues of a deep sea diver who does not use the

special suit and equipment for sea diving 5. What is another name for decompression sickness? Challenge: Jellyfish are living creatures that often live hundreds of metres below the surface of the ocean. Suggest how the body of a jellyfish is adapted to survive in areas of such high pressure.

Year 8 Science Lessons PHYSICS LESSONS Lesson 1 ......Lesson 2: Levers in Action Lesson Purpose:...

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Transcript of Year 8 Science Lessons PHYSICS LESSONS Lesson 1 ......Lesson 2: Levers in Action Lesson Purpose:...