How do you explain to a five year-old what energy is?
The other day I told my son to not waste hot water, as it is a waste of energy. He then asked what that is. I want to explain it well, also from a physical point of view, since I find it important. What shall I tell him?
Update:
Thank you all very much. Energy appears to be too abstract to explain to a 5 year old in terms of physics. It is definitely not done in one day. I showed him the meters for gas, electricity and water today and explained that we have to pay what we consume, and we can not spend that money elsewhere. That would be the value of resources, which really matters.
On explaining energy, I think the best answer was to make him rub his hands, converting mechanical into thermal energy. And on that basis one can start to explain conservation of energy and it's different forms. Much later, one can try to explain that some forms of energy are more versatile than others, and, if one has an understanding, why that is.
Again, thanks a lot, I will check the answer that suggested to show the meters, but most others were also good.
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Well energy is basically movement. What helped understand was seeing things under a microscope. I found it very interesting and entertaining.
When he wakes up in the morning, he has a LOT OF ENERGY!
He wants to run around and play! He can do this all day!
But slowly, he gets tired the more he runs.
At the end of the day, he'll notice he wants to sleep. He has used up most of his energy!
Some people work very hard to make energy for heating up the water, so don't waste it?
Find a game that uses some kind of energy, whether it's magic points or player energy or run speed or something like that.
Kids latch on to games and they will quickly realize they don't have enough energy for every single thing they want to do. Once they have a good understanding of this concept, you can start to apply it to all kinds of resources that are limited. We don't want to waste food because the family has limited money. We don't want to waste gas because the world has limited hydrocarbons (or as you tell him, raw oil to make gas from). We don't want to leave the TV on or hot water because there's a limited amount of energy no matter where it comes from.
You can explain to him what energy is easy enough, but he needs to understand resource management before he can understand what wasting really is. Like many difficult concepts, games naturally convey these lessons in modes he can understand.
If you have a wind-up flashlight (a flashlight with a hand generator), you can make this very simple. Have the child turn the crank to give the battery a charge. Then ask them how they would feel if they had turned the crank for an hour, then they saw someone turn on the flashlight, leave it on, and walk away.
Both the physics and the English of this answer are sound. Energy was used to turn the crank. Letting the flashlight run without using it is clearly a waste of that energy. Additionally, the child should be able to understand what is wrong with it more easily when it was his energy that got wasted.
Energy is potential. It gives us the ability to do something useful.
So there's energy coming into the house, and it has the potential to provide light, heat, and motion, but until we connect it it's only potential.
Once we turn on a switch, or plug in the fan, the energy is converted into light or motion until we turn the switch or fan off.
You have energy - your body converts food into energy, and stores it as sugars and fats. Then, when you want to move your arm or legs, your body uses those sugars and fats to make the muscles work.
The house doesn't use food - there are companies that provide energy to use in wires and pipes, giving us gas and electricity. The water also comes through a pipe, and we use some electricity or gas to heat it up.
The more hot water you use, the more energy the house uses to keep it hot for you, and the more we have to pay these companies who feed the house its energy.
Late to the game, but I'll add my 2 cents. Maybe a long 2 cents.
I would say that energy is what does work. In terms he can understand for the hot water, have him rub his hands together (palm to palm) until they warm up. (You can explain friction in simple terms, or hold off.) When he rubs his hands together, friction causes his hands to warm up. The energy he uses to do the work of rubbing his hands is converted to heat. Limp hands/arms use no energy and do no work. Moving hands/arms use energy and do work.
He can probably understand intuitively the transfer of heat. Ask him to imagine that he had to heat water by rubbing his hands until they got hot, then held his hands to a vessel of water, over and over until the water warmed up enough to bathe in. That represents a lot of work to heat up water. It shouldn't be wasted.
I found that clear chandelier bulbs on a dimmer switch were ideal to take the concept of work/friction = heat/ light.
At a minimum setting, one is forcing electricity (no need to explain everything all at once) through a tiny metal wire, and that, like rubbing your hands, causes the wire to heat up (friction). He can actually see the heat as the wire glows a dull, dark orange, and he can feel the heat by feeling the bulb. As you turn the switch up, you force more electricity through the wire, heating it even more, till it glows white-hot, and is too hot to touch. Energy was turned into heat and light.
Finally, explain that there are coils in a water heater, and the same principle applies: energy driven through the coils causes heat, which warms the water.
Work is good and important, but wasted work doesn't help anyone.
Mostly, this works (no pun intended) if it is worked into everyday conversation. If you have an electric range, show him how the coils heat up and why (same as the metal filament in a light bulb.) If he feels the sum warm his face, he's feeling the sun's energy as heat. The sun gives off light, just as the wire filament does. As long as he's interested, there are examples everywhere of energy, work, heat, light, movement (cars, trains), and construction (bulldozers, carpenters, cranes, etc. When he gets older, your explanations can become more sophisticated (plants do work - construction - to grow and make food. The energy to do the work comes from the sun.) Electrons move through things and heat them and cause light and do work. We call that energy "electricity" after the electron's work. If the electron doesn't move, like his limp arms, it does no work.
The story of electrons is fun, too. Science is ripe for study all around us.
Of the existing answers I think A E's is excellent, I will just add that you might also want to explain/emphasis that energy is not just something that exists that can be consumed for various purposes and then is disappearing afterwords (e.g. the first law of thermodynamics).
Fuel in a car is stored energy that transfers into motion, heat and sound.
Wood that is burned transfers into heat and light, sometimes sound as well. A ball pushed of the edge of the table transform into motion and sound.
The energy of the electricity coming into the house will always transfer into something else. Help him come up with examples of this on his own, for instance
TV - Light, sound, heat
Washing machine - Motion
Water heater - Heat.
Here's one explanation aimed at primary-age children which is probably basic enough, although of course it's focussed on what energy does and what we use it for, rather than what energy is. But that's probably the best you'll get them to understand at this age.
Energy Makes Change
Energy makes change—it produces a change of some kind; it does things for us. We use energy to move cars
along the road and boats over the water. Energy is used to bake a cake in the oven, and to keep ice frozen in
the freezer. It provides power so we can listen to our favorite songs on the radio, and light our homes. Energy
makes our bodies grow and allows our minds to think. Scientists define energy as the ability to do work.
Energy is found in many different forms such as light, heat, motion, sound, and growth.
"What Is Energy?", Primary Energy Infobook (p.7), National Energy Education Development (NEED) Project
I teach Electrical engineering and physics to 5-7 year olds. I just replace the word electron with magic, and energy with "the force". later, when they want to argue with me, we can discuss it further. I try to not let language be the barrier that stops kids from learning, and being observant.
I try to teach an applied and observed perspective of science, which works out to making fun stuff to play with, if you are a kid. Let them observe, and make mistakes/ find ways to challenge them into changing their mind.
"There is no such thing as magic"
coming form the same person who still believes in the Easter bunny, switch witch, tooth fairy, Santa, and monsters under the bed.
flip a light switch, and say ok, what made that light come on if not magic?
Richard Feynman tells this story in "Surely You're Joking, Mr. Feynman":
It was the kind of thing my father would have talked about: "What makes it go? Everything goes because the sun is shining." And then we would have fun discussing it:
"No, the toy goes because the spring is wound up," I would say.
"How did the spring get wound up?" he would ask.
"I wound it up."
"And how did you get moving?"
"From eating."
"And food grows only because the sun is shining. So it's because the sun is shining that all these things are moving." That would get the concept across that motion is simply the transformation of the sun's power.
Note carefully that Feynman's father didn't say the word "energy." Judging by the first chapter of the same book, that was probably on purpose.
Energy is not a tangible thing, it isn't something you can touch, see, hear, taste or feel, energy is a concept, just like a number is a concept, just like speed is a concept. It's not a real thing like a tree, a bacteria, water, or the Sun.
And because energy is a concept, it is misleading and a source of confusion to use language such as "waste energy", or to say that some object "has energy", because how can you waste something that is not real, and how can an object possess something that isn't real?
So don't tell your son that wasting hot water is a waste of energy. Teach him instead what it takes for him to be able to have hot water for his shower. You may have to do some reading up on your part, but then you will both learn something!
Tell him that water is transported to your home through underground pipes, and when it reaches home and your son turns the hot water knob, this water gets heated, usually with gas or with electricity. (If he is interested this could be a good opportunity to explain to him how gas and electricity can heat water: gas is ignited and burns; electricity is a bunch of tiny particles moving inside a material which make the material get hot, and when this material is near water it heats the water).
If your water heater runs on natural gas, tell him that gas is extracted from deep beneath the ground, which takes a lot of effort, and that there is not an unlimited supply of gas below the ground: the gas that is burnt cannot be used again.
If your water heater runs on electricity, tell him that in order to generate electricity (i.e. to get the bunch of tiny particles moving) people usually burn coal or burn gas. Just like gas, coal comes in limited supply (and burning coal isn't nice for the environment: en.wikipedia.org/wiki/Coal#Environmental_effects). There are also the radioactive nuclear fuels which come in limited supply as well, but it would be difficult to explain to a 5 yo how those are used.
Bottom line is it takes a lot of effort from many people to gather natural resources which in the end allow your son to have hot water, these resources are in limited supply, and the more he wastes hot water the more he uses up these limited resources. So by not wasting hot water he thinks about others and not just about himself.
Now if you want to explain to your son the physical concept of energy this isn't straightforward. How would you explain it to a 30 yo?
Personally I think we would be better off without the concept of energy at all. The concept doesn't explain anything, worse than that it hides real explanations and gives people the illusion they understood something while in fact they haven't understood anything at all.
To give an example, often people say that a ball thrown upwards decelerates on the way up 'because' its kinetic energy is converted into potential energy, and then accelerates on the way down 'because' its potential energy is converted into kinetic energy. But an abstract concept cannot be the cause of anything! This is called the fallacy of reification, the logical fallacy of treating a concept as a real thing, as a cause.
There is no real thing inside the ball called kinetic energy that gets converted into another thing called potential energy. The ball decelerates on the way up because it accelerates towards the Earth, and it accelerates on the way down because it keeps accelerating towards the Earth. Then we can wonder why the ball accelerates towards the Earth, but the concept of energy will never answer "why" to anything, it can only serve to describe "how". Kinetic and potential energies are just numbers that we can use as intermediaries in calculations. In fact we could reformulate the whole of science without the concept of energy and still describe the universe as accurately.
To give another example (that the concept of energy is a source of confusion and doesn't explain anything), you didn't know how to explain to your son what the concept of energy is, your son didn't understand what you wanted to tell him, and the concept prevented you from realizing that all you had to tell him is that the Earth has limited resources and wasting hot water is wasting these resources.
So if I had to explain what energy is, I would say that it is a dispensable mathematical tool widely used in science and which is a source of much confusion.
My six and eight year olds know energy as "the ability to do work" or, as AE mentioned, the ability to change something.
Make the water hotter? That is change and requires energy.
Bounce more photons off the walls so that our eyes can collect enough photons to see? Those photons move very fast so it takes a lot of work (energy) to move them.
Note that I gave two definitions. I try to do this with most principals (scientific and moral) and then I show them how both definitions are equivalent. This makes it easier to explain things from multiple angles. It also gives them more tools to explore the world around them and come to their own conclusions. Then when your child asks where does the energy come from to push the water out of the tap so fast, you'll be able to ask them how they realised that it requires energy and you'll both be proud!
Energy is the power to do things. I'm sure your 5 yo is full of it. When he is full of energy he can run and play for hours on end and have a good time. When he runs out, he can't do that any more and needs to sleep and eat to build up more so he can play again.
There are many kinds of energy, like electrical and heat. Electrical energy lets the lightbulbs shine and lets the TV run. Heat makes the water (or the house in the winter) nice and warm. Chemical energy (like what we "store" (ie. potential energy) in gasoline) lets us move cars so we can go places faster, like the park or grandma's house. There are plenty of other kinds and examples of energy and how we use it.
Once he knows that energy lets us do all these awesome things and that getting back energy is hard (ie. if you want energy to play you have to eat and spend all that time sleeping, or you have to spend money to buy electricity / gasoline, etc) it should be pretty easy to explain why we don't want to waste the energy we put so much effort into getting.
I would say "We get energy from eating food" and we need energy to ride bycicles or to run,etc. He might easily understand that he can only play if we has energy and he can get plenty of it by eating.
These other answers seem too abstract for a 5-year-old. I don't think he's ready for that yet. Stick to the visible and concrete. Take him outside and show him the power cables going to your house, that lead into your fusebox/meter.
Show him the meter moving. Explain to him that there's a company that makes electricity (not quite the right words scientifically, but let's keep it simple) and sends it to you over those wires. Those wires then go into the house, to the outlets where you plug things in.
Things like the blender; the computer, and bigger stuff like the oven and water heater. As you use electricity, the meter counts how much and then the company sends you a bill. Show him the bill.
If you want to get a bit more eco-friendly, mention to him that the company that makes the electricity does it by burning coal and we want to minimize that, too.
You can tell him that energy is like food (or better yet, sweets) and say him (if he understands the concept of money; which he will probably understand, because 5 years old children already are grown-up enough for it) that you can't buy too much food, because money may run out, and it's the same for energy.
So you can just tell him that water, especially hot, costs much money is wasted.
In the Oxford dictionary there are two relevant definitions: power derived from using physical or chemical resources; or a property of matter and radiation, manifested as a capacity to perform work.
The second (Physics) definition really (for any understanding) requires you to continue to explain how, for example (and amongst many other things), photons interact with electrons. You'd have to do more research yourself to understand all the known or theorized physical interactions.
The first definition is arguably less technical, and if you asked me what to tell a 5 year old, I'd start with this definition.
I'd explain (to start to provide information for your 'waste' discussion) that, to get these physical 'resources', great amounts of human work must be done. Gas, for example, must be found, captured, and delivered in a bottle to your house. Ask how hard they think that would be.
And in reality, providing gas -- or any useful 'energy resource' -- at the price we pay requires and required huge amounts of human effort.
Notice that there's plenty of energy that isn't useful to humans: the Sun releases great amounts of radiation with energy and most of it is not used by humans.
'Wasting' energy -- and what that might or might not really mean -- is a different topic that you didn't really ask about, so I won't discuss that here.
stored motion
when you bring a pencil up, and let it go, it starts moving
when a child eats a chocolate, it uses the chocolate to power its movements
when you connect a blender to a power outlet, it uses the energy in the wires (whatever that is =P) to move
when you put gas in car, it burns the gas and moves
when you burn something, it releases "energy", and things around it get hot (and heat is a kind of motion)
storing motion
when, lying down, a child throws a (small) ball up, they can see it go up, stop, and come back. It is storing motion into height, and then getting motion back from height (try it yourself with a small plastic ball. Lie down and throw it right up)
when you pull a slingshot, you are storing energy. When you release it, the rock gets in motion
when you compress a spring you are storing energy. Then you release it, and it moves (carefull with eyes =P)
sunlight heats things. so it has energy. plants use that energy to grow (https://www.youtube.com/watch?v=VZdi4fj-hWc) - and that is motion. But they keep some energy stored. Then a cow comes, eats the grass, and uses it to move around. Then we come and eat the cow... Or maybe the cow dies, and is buried, and turns into petroleum, and then we can use this "cow juice" to power up a car (that is, to make it move)
if you are feeling adventurous...
Energy cannot appear from nowhere
Funny enough, I just thought about the same question for myself two days ago. My abstract answer (I am a physicist) was - without consulting books: "energy is the property of a physical system required to invokes the change of state of a physical system. Energy can be tranferred from one physical system to another (invoking change of state) and can be stored for a while but never destroyed". Sure this would be far to abstract for a 5 year old.
For a five year old -like my daughter - I'd say:
Energy is something inside the things which causes change. And it takes different forms. Examples: if you run you change your location and you and your body. Then you have energy of movement (kinetic energy). Or it can heat things up like a pot of water heated on the stove.
It can be passed from one thing to another to make things move for instance: if you kick a ball, the energy of movement of your foot is passed from your foot to the ball. In the heating water example energy is transferred from the burning gas (chemical energy) to the pot to the water causing the water molecules - my daughter understands this already - to move quicker and quicker until they are that fast so they are ejected from the water as steam.
Interesting - if one starts to think about such thing one notices how difficult it is to explain....
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