# Explaining electricity kWh to a primary school

Since getting an electric car and not knowing much about kWh I feel totally noob in understanding kWh. My son is really interested in why some chargers charge slow and some really fast. Since I didn't have my father (he passed away when I was 8) to explain much things in life I want my son to have knowledge of things he ask me

How do make understand what is kWh to a 6-year-old with an example of non-electricity but still give the example?

• Not an answer but it is great that you're trying to find out how to answer your son's question! It is easy to say you don't know or to ask someone else so it's inspiring to see someone who'll learn themselves in order to teach their child. Commented Apr 9, 2022 at 12:40

First you need to make sure that your own understanding is reasonably correct. Otherwise you'll be doing more harm than good. You can start watching some introductionary videos like this one: https://www.youtube.com/watch?v=zKb3QRyIDnM. You can google this and see which videos you like. You may even be able to watch some with your son together.

The key points are

Energy is the ability to do work: Lifting something light is easy. Lifting something heavy is hard. You need energy to lift something, that's where the work comes from. If you lift something that weighs 2kg you need twice the energy as if you lift something that weighs 1kg. You can do a fun exercise with your son, lifting up a few objects and then throwing them on the scale to compare.

Energy also adds up. Lifting an object 10 times requires 10 times the energy as lifting it once. Again, that's something you do with your son together.

Energy can be measured. There are multiple units for energy: Joules, Calories, kWh etc. They are just different names for the same thing. Energy that you body uses comes from food. The more calories are in the food the more energy you get and the more you can lift. You can sit down with your son and look at some food labels.

An electric car needs energy to move. The longer it moves, the more energy it needs. This energy is measured in kWh.

Energy comes in all different types of form: food (chemical), electricity, heat, sound, motion, light, etc. It can be converted from one to the other but it's never created or destroyed. The term "energy generation" is actually a misnomer!!

Examples: Your body transforms food energy into motion energy. An electrical car transforms electrical energy into motion energy. A solar panel transforms light & heat energy from the sun (which you can feel on a sunny day) into electrical energy. A wind turbine transform motion energy of the wind into electrical energy etc.

You can play a game with your son where you look at pictures or anything at home or outdoors and search for examples where energy is converted from one way to another. If you see a car go by: fuel energy (chemical) is converted to motion energy (it moves) and sound energy (it's loud). A squirrel climbs up a tree: it converts food energy to motion energy, etc. Pretty much everything you see that changes in some way form or shape involves some energy conversion.

Explain it by analogy with a hose that fills an above ground pool. Big hose is similar to high power or high kW. Fill it up longer and you get more water pumped up into the pool, similar to higher energy or higher kWh.

Or get a hand crank flashlight and show how in the dark it glows brighter when you crank it faster. That is higher kW, or higher power. The total output over time is energy expended or kW.

I actually have a better idea. Ask your question on Reddit on ELI5. This is “explainlikeimfive” subreddit. The best answers there are quite a bit better than whatever I can come up here. You have to wait a few days for the answers to appear. Good luck!

For a 6 year old the best is to use an analogy with water. The battery in your car is like a bucket - it can be filled with energy just like a bucket can be filled with water. And then it can release the energy to the car motor when you drive.

A bucket has a capacity (its "size" or volume) measured in Litres or Gallons. Likewise the battery has a capacity ("size") measured in `kWh` - kilo watt hours.

Now why some chargers are faster then others - think of how you can fill the bucket. You can use a straw but it will take a long time. Or use a garden hose and it will fill faster. Or have firehose and it will fill almost in no time at all.

These hoses are like different chargers. There is only so much energy / water that you can push through a small charger / small hose, so it takes a long time. A specialised fast-charger or a fire-hose can deliver the same amount of energy / water in a much shorter time.

The analogy works even further - why not all chargers are the fast kind? Well because there is no power infrastructure to deliver the energy quick enough. Not everyone can have a fast charger at home just like not everyone has a firehose at home. That's why your home charger may be slower than a commercial one.

Now on the kilo watt hours: a 10 kWh battery can feed the car motor with 1 kW for 10 hours (easy cruising) or it can deliver 10 kW of power for 1 hour (e.g. when going uphill it needs more "juice"). That is 10 kW * 1h = 1 kW * 10h = 10 kW*h = 10 kWh. So the battery capacity shows how much power and for how long can the battery deliver to the motor.

Then of course there are other things to consider. For example that frequent fast-charging shortens the battery life and it's better to slow charge when you have the time. However why that happens is way above the 6 years old level.