How can I explain the purpose of flywheel in car Engine to a 10 year old child?
Daniel Becker, Patent Attorney and Early-stage Engineering (2013-present)
There are two functions of a flywheel:
- to maintain engine momentum, for smoothness
- to minimize the amount of energy lost with each firing, particularly at constant speed, for efficiency, and power. In other words, avoid the load recurringly being SO high that the engine can barely keep running.
Take a child to a park with a hand-pushed carousel. Like this:
File:Manually powered carousel on a playground in Saint-Petersburg.JPG
I am presuming that a child understands that a car engine uses pistons which push on a crank, or at least uses chambers that contain explosions, and each explosion is used to push the car… and that ~somehow~ the output of the engine is a spinning shaft.
for smoothness:
get the child onto the carousel, and push… maybe only occasionally. And relatively gently. Not every handle. See if you can do it so that one push just barely gets the carousel all the way around. Have the child count how long it takes to go around once. Then, have the child count how long it takes to go only HALFWAY around, the first half. Then, have the child count how long it takes to go the second half. The second half should be longer.
[optional]: have the child push on the ground, when the carousel is halfway around.
Then, join the child on the carousel. Then try to manage a push that just barely gets you around, pushing on the ground. do the same count, and try to get it down to about the same amount of time to do a revolution as before. Then, when that is about the same, you count the first half, and the child counts the second half. The difference between the two should be smaller than before.
[optional]: [actually,.. this may be better]:
HAVE THE CHILD push on the ground again, when the carousel is halfway around.
THEN… ask the child whether it was easier to push the carousel when they were by themselves, or when you were both on it.
[ if you want to go further, to demonstrate how a bigger/ heavier flywheel increases the effect]:
YOU get on the carousel, and have the child push the carousel, while you are near the outermost part of the carousel. THEN, have the child do it again, while you sit as close to the middle as possible.
Ask the child which was easier to keep the carousel at the same amount of time for each lap. NOT whether it was easier to make you go faster, but… controlling for how long it takes to go around, whether it was harder with you at the center or near the outside.
FOR stalling/ overcoming ongoing burdens that slow an engine:
Get onto the carousel. and have the child try to push you. Rather than standing still, have the child push by running a quarter of the way around the carousel as they push.
Then, instead of just stopping moving at the end of the quarter-lap push of the carousel, have the child push for the same quarter of a lap, and at the end of the push, JUMP ON.
Then, after several laps, ask the child whether it was easier to keep the carousel moving, or even make it move more quickly and steadily, when adding their mass to the carousel each time.
How about that?
(I’m quite proud of that idea. I’ll try to show that to my daughter sometime. She’s 8).
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Daniel Becker, Patent Attorney and Intellectual Property Attorney 
