Lesson video

Hello, everyone.

How are you today?

I hope you're feeling really good.

My name is Ms. Afzal, and I'll be your teacher for this lesson, which I'm feeling very pleased about because today we've got quite an interesting topic ahead.

We're gonna be looking at energy.

In particular, we're looking at "Transferring energy.

" That's the title of our lesson.

It comes from the unit of work "Forces.

" I hope this all sounds of interest to you.

So if you are ready with some energy, focus, and enthusiasm, we'll begin our lesson now.

The outcome for today's lesson is I can identify when stores of energy change and describe causes of energy transfer between stores.

I hope that sounds of interest to you.

We have some keywords in our lesson.

Let's go through them one at a time, saying them out loud.

Store of energy.

Surroundings.

Energy transfer.

Great to hear those keywords.

And now pause here and share with someone, do you know what any of these keywords mean?

Thanks for sharing.

Let's find out the definitions.

A store of energy describes the different ways in which energy can be stored.

An object's surroundings include everything that is around it.

An energy transfer takes place when the amount of energy in some stores decreases and increases in others.

So these are our keywords: store of energy, surroundings, and energy transfer.

Let's look out and listen out for them.

They'll be coming up in our lesson today.

Today's lesson is called "Transferring energy," and it has two learning cycles: changes in energy stores and causes of energy transfer.

Let's begin by exploring changes in energy stores.

There are several different stores of energy, including gravitational, thermal, elastic, chemical, and kinetic.

When a ball falls, its height decreases and its speed increases.

So here's before, the ball is high up and stationary.

And then after, the ball is lower and moving.

Between the two snapshots, the ball's gravitational store of energy decreased and the ball's kinetic store of energy increased.

Let's have a check for understanding.

Put each statement into the correct box in the table.

So we have the stores of energy which are gravitational and kinetic, and you need to say when they are increased and when they're decreased, either by an object being raised higher, an object slows down, an object speeds up, or an object is lowered.

Pause here while you put each statement into the correct box in the table.

I wonder if you put the statements into these boxes.

The gravitational store of energy increases when an object is raised higher and decreases when an object is lowered.

Kinetic store of energy increases when an object speeds up and decreases when an object slows down.

Well done if you put the statements into these boxes.

A person's body has to work to stretch a stationary spring.

So before, the string is unstretched, and after, the string is stretched.

And in between these two snapshots, the person's chemical store of energy decreased and the spring's elastic store of energy increased.

All of these involve a chemical store of energy changing: burning fuels, taking in food, a plant growing, a human body moving or moving an object, some life processes, e.

g.

pumping blood, and recharging or using a battery.

They all involve a chemical store of energy changing.

Let's have a check for understanding.

Does each of these cause the chemical store of energy of the object to increase or decrease?

So we have a candle burning, grass growing taller, a person doing a pushup, a person eating, a torch left on all night, a person walking upstairs, a person standing still in a lift, a mobile phone charging.

Decide whether the chemical store of energy of the object increases or decreases.

Perhaps you came up with these answers.

For a candle burning, the chemical store of energy decreases.

For grass growing taller, it increases.

A person doing a pushup, decreases.

A person eating, increases.

A torch left on all night, decreases.

A person walking on stairs, decreases.

A person standing still in a lift, decreases.

And a mobile phone charging, increases.

Let's have another check for understanding.

Describe how the stores of energy of the person and the toy changed when the toy was lifted onto a shelf.

So before, we have the toy stationary and lower, and then afterwards, the toy is stationary and higher.

And what happens between the two snapshots?

The person's store of energy decreased and the toy's store of energy increased.

Pause here while you fill in the gaps in these sentences.

Perhaps you completed the sentences in these ways.

The person's chemical store of energy decreased and the toy's gravitational store of energy increased.

When a cup of tea cools down, it transfers some energy to the surroundings, the air in the room and the tabletop.

So here we have a before and an after-10-minutes image.

Between the two snapshots, the cup of tea's thermal store of energy decreased and the surroundings' thermal store of energy increased.

Let's have a check for understanding.

Describe how stores of energy of the candle and the surroundings changed between the two snapshots.

So before and then after, 30 minutes later.

Complete these sentences.

The candle's store of energy decreased and the surroundings' store of energy increased.

Pause here while you complete these sentences.

Perhaps you completed them in these ways.

The candle's chemical store of energy decreased, and the surroundings' thermal store of energy increased.

Objects often transfer energy to the surroundings' thermal store of energy in addition to their intended effect.

These transfers can be caused by friction between two surfaces, electrical devices warming up, hot parts of machines, the movement of living things, and objects emitting light or sound.

Let's have a check for understanding.

Describe how the stores of energy of the car and the surroundings changed between the two snapshots.

So here's the before image, the toy car moving, and after, the toy car has come to a stop.

And here are the sentences.

The car's store of energy decreased, and the surroundings' store of energy increased.

Pause here while you complete these sentences.

Perhaps you completed the sentences in these ways.

The car's kinetic store of energy decreased, and the surroundings' thermal store of energy increased.

Let's have another check for understanding.

This LED torch is accidentally left on for 24 hours.

The battery goes flat.

Describe how the stores of energy of the torch and surroundings changed between the two snapshots.

So we have a before image and then after 24 hours.

And here are our sentences.

The torch's store of energy decreased, and the surroundings' store of energy increased.

Pause here while you complete these sentences.

Perhaps you completed the sentences in these ways.

The torch's chemical store of energy decreased, and the surroundings' thermal store of energy increased.

And one more check for understanding.

Mr. Orange does 20 minutes of high-intensity exercise.

Sounds good.

Describe how the stores of energy of Mr. Orange and the surroundings changed from before the exercise to 10 minutes after.

So before, Mr. Orange is stationary, core body temperature of 37 degrees.

Afterwards, he's a bit puffed out and sweaty.

And then 10 minutes after that, he's stationary again with a core body temperature of 37 degrees.

So here are our sentences.

Mr. Orange's store of energy decreased, and the surroundings' store of energy increased.

Pause here while you complete these sentences.

Perhaps you completed the sentences like this.

Mr. Orange's chemical store of energy decreased, and the surroundings' thermal store of energy increased.

And now it's time for your first task.

I would like you to describe all the stores of energy that changed in each example.

So number one, a person spun a spinning toy.

Two, the spinning toy stopped.

Three, a stretched catapult is released.

Four, a toy car rolled down a slope.

Five, a petrol car gets faster.

And six, a Bunsen burner heated water from 0 to 80 degrees Celsius.

Pause here while you describe all of the stores of energy that changed in each example.

I'll see you when you're finished.

It's good to be back with you.

So how did you get on with that task, describing all the stores of energy that changed in each example?

In our first example, a person spun a spinning toy.

I do find those very pleasing to spin.

The person's chemical store of energy decreased, and the toy's kinetic store of energy increased.

The surroundings' thermal store of energy also increased.

Next example, the spinning toy stopped.

The toy's kinetic store of energy decreased, and the surroundings' thermal store of energy increased.

Next, a stretched catapult is released, and the catapult's elastic store of energy decreased, the ball's kinetic store of energy increased, and the surroundings' thermal store of energy increased slightly.

How about the toy car rolling down the slope?

The toy's gravitational store of energy decreased, the car's kinetic store of energy increased, and the surroundings' thermal store of energy increased.

And let's take a look at our last two examples.

A petrol car gets faster.

The car's chemical store of energy decreased, the car's kinetic store of energy increased, and the surroundings' thermal store of energy increased.

And how about the Bunsen burner heating water from 0 to 80 degrees?

The Bunsen's chemical store of energy decreased, the beaker and water's thermal stores of energy increased, and the surroundings' thermal store of energy increased.

Well done, everyone, for having a go at this task.

And now we're onto our next learning cycle, causes of energy transfer.

When a store of energy decreases, other stores of energy must increase by the same amount.

So here we can see the candle's chemical store and the surroundings' thermal store.

And here we can see the candle's chemical core has decreased and the surroundings' thermal store has increased by the same amount.

This is called an energy transfer because an amount of energy has moved out of one store and into another.

Energy cannot be created.

A store of energy can only increase if another store of energy decreases.

For a falling ball, ignoring air resistance, this is not possible.

So we've got the ball's gravitational store and the ball's kinetic store.

It's not possible for the ball's gravitational store to decrease by a certain amount but the ball's kinetic store to increase by a much larger amount.

The kinetic store of energy must increase by the same amount that the gravitational store of energy decreased.

Energy also cannot be destroyed or used up.

It can only be transferred to another store.

For a falling ball, ignoring air resistance, this is also not possible.

Here we have the gravitational store and the kinetic store.

The gravitational store is decreasing by a certain amount, and then the ball's kinetic store is increasing by a much smaller amount.

The increase of the kinetic store must be by the same amount as the decrease of the ball's gravitational store.

Let's have a check for understanding.

Which of these diagrams could show the changes in stores of energy for a falling ball?

Choose from A, B, or C.

Well done if you selected answer A.

Indeed, the kinetic store has increased by the same amount that the gravitational store has decreased.

The idea that energy cannot be created or destroyed, only transferred between stores, is called the law of conservation of energy.

The law of conservation of energy can tell us what is possible and what is impossible.

A ball released from here from rest will never be able to roll above the line.

Everything in the universe obeys this law.

A rolling football has a kinetic store of energy.

As the football rolls, it hits blades of grass, making them move.

Some of its energy is transferred to the grass.

The football also hits air particles as it rolls.

Some of its energy is transferred to the air.

As the ball slows down and stops, its energy is not used up or lost.

Its energy is transferred to the surroundings because of the forces of friction and air resistance.

Let's have a check for understanding.

Which is the best explanation of what happens to this car's energy?

So we have the toy car moving, and then the toy car has come to a stop.

Choose from these options.

A, the car's energy was used up keeping the car moving.

B, the car's energy disappears.

C, the car's energy disappears into the surroundings.

D, the car's energy is transferred to the surroundings.

Pause here while you decide.

What's the best explanation of what happens to this car's energy?

Well done if you selected answer D.

Indeed, the car's energy is transferred to the surroundings.

We've seen that energy transfers can be caused by forces: gravitational forces, friction and drag forces, pulling forces.

Energy transfers can also be caused by chemical reactions, including within your body, contact between objects at different temperatures, electricity, and absorbing or producing sound or light.

Let's have a check for understanding.

What causes energy to transfer from a chemical store to the thermal store of the surroundings in a firework?

Choose from the following.

A, electricity, B, a chemical reaction, C, a force.

Pause here while you decide.

Well done if you selected answer B.

Indeed, it's a chemical reaction.

Let's have another check for understanding.

What causes energy to transfer from the gravitational store to the kinetic store of the skydiver as they fall?

Choose from the following.

A, electricity, B, a chemical reaction, C, a force.

Pause here while you decide.

Well done if you selected answer C.

Indeed, it's a force.

And now it's time for your next task.

For each example, I would like you to describe: A, how the named stores of energy have changed, B, what caused the energy to be transferred.

So here are our examples.

Number one, chemical store of the candle and thermal store of the surroundings.

Two, gravitational store of the car and kinetic store of the car.

And three, chemical store of the person and gravitational store of the giraffe.

So pause here while you have a go at this task of describing how the named stores of energy have changed and what caused the energy to be transferred.

I'll see you when you finish your task.

It's great to be back with you.

How did you get on with that task of describing how the named stores of energy changed and what caused the energy to be transferred?

So for example 1, the amount of energy in the chemical store has decreased and the amount of energy in the thermal store of the surroundings has increased.

And B, this was caused by the burning of the wax, a chemical reaction.

Example 2, the amount of energy in the gravitational store has decreased, and the amount of energy in the kinetic store has increased.

This was caused by the gravitational force pulling the toy car.

And our final example.

The amount of energy in the chemical store of the person has decreased, and the amount of energy in the giraffe's gravitational store has increased.

This was caused by the person lifting the toy giraffe using their muscles.

Well done for having a go at this task, everyone.

In our lesson, "Transferring energy," we've covered the following.

Stores of energy can increase or decrease when there are changes in speed, height, temperature, length, and during chemical reactions.

When stores of energy decrease, other stores of energy have to increase by the same total amount.

Energy cannot be created or destroyed, only transferred.

Forces can cause energy to be transferred between stores of energy.

Energy can also be transferred when an electric current flows, when there is a difference in temperature between two objects, when there is a chemical reaction, and when light and sound waves interact with matter.

Well done, everyone, for joining in with this lesson.

It was great to explore this topic of transferring energy together with you.

Let's be on the lookout for energy transference as we go about our daily lives.

It is happening everywhere.

It is the law.

The law of conservation of energy is all around us.

I hope you enjoyed this lesson.

I really enjoyed teaching you, and I hope to see you at another lesson soon.

Until then, stay curious.