# Flywheels and Rotational Motion

One possibility for a low-pollution automobile is for it to use energy stored in a heavy rotating flywheel of mass 240 kg, and should be able to travel 300 km (300,000 m) without needing a flywheel "spinup."

Make reasonable assumptions (avg. frictional retarding force 500 N, 20 acceleration periods from rest to 90 km/h or 25 m/s, equal uphill and downhill --assuming during downhill, energy can be put back into the flywheel), and show that the total energy needed to be stored in fly wheel is about 1.6 x 10^8 J.

I need help to start this proof. Do you use K_i + U_i = K_f + U_f? What do I do from here?

Thanks for any pointers.

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try using K_rotatational also
k_rot = (1/2)IW^2 --> I is inertia, W is omega (angular speed)

Integral
Staff Emeritus
Gold Member
What happens to the energy stored in the flywheel if you should be come involved in an accident? I have visions of a massive flywheel with a large rotational kinetic energy busting loose from its housing and ripping off down the road destroying car after car, each of which releases a flywheel! :surprised Talk about a chain reaction accident!

Yeah, I know that is a bit extreme, but containment is an issue.

Also spinups will be necessary. Suppose I drive from my home at 100m to spend a week in the mountains at 1000m? A spinup may well be necessary to meet my needs for a week. Now on the way home, I may find myself with more energy to store then the flywheel is designed for.

Just some thoughts, the fact is, for years I have speculated about using a flywheel for automotive energy storage.

Integral
Staff Emeritus