Cars have come a long way since the days when horses pulled us in buggies. First came cars that ran on gasoline, but those dirty the air. Now some people have electric cars, which run on a battery like your favorite toy or flashlight. But it’s a BIG battery that can drive the car for many miles. So Elsie H. asked us a great question: how much energy does an electric car need to drive 1 mile? Let’s look at a Nissan Leaf driving on flat ground. Just to compare, when you turn on a 40-watt light bulb in your house for 1 hour, it uses 40 watt-hours of electricity. The Leaf can drive 100 miles on 34,000 watt-hours (34 thousand), so it’s using only about 340 watt-hours per mile…the same as leaving that little light bulb on for a little more than 8 hours. Tesla’s cars use even less, about 250 watt-hours per mile. Imagine how fast one of those batteries could drive a toy car!
Wee ones: What shape are the wheels on a car (like in Elsie’s picture)?
Little kids: If a little AA battery can run your toy car for 5 hours, will that last from 2 in the afternoon until 6 at night? Bonus: For how many hours could 2 full AA batteries run the car?
Big kids: If you can drive 100 miles on the Leaf battery and you’ve driven 60 so far, how much farther can you drive? Bonus: If that same battery could run your toy car 100 times as far, how far could your toy car drive on a full battery?
The sky’s the limit: If a fully charged Leaf battery can light a bulb for 800 hours OR drive the car for 100 miles, how far can it drive the car if you first use it to light a bulb for 200 hours?
Wee ones: A circle (or when donut-shaped, a “torus”).
Little kids: Yes! because that’s only 4 hours. Bonus: 10 hours.
Big kids: 40 miles left. Bonus: 10,000 miles, or about halfway around Earth!
The sky’s the limit: 75 more miles. If it ran the bulb for 200 hours, that used 1/4 of its energy, so it can now drive only 3/4 of its usual 100 miles of distance.
And thank you Elsie for the awesome question and equally awesome drawing!
Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.