Flywheels can receive power from more traditional sources, as well. For instance,
uninterruptible power sources (UPS) for computers use rechargeable batteries to keep
computers powered during short-term power outages. Flywheels are being considered
as an alternative to chemical batteries in these systems. Less traditional sources can
also supply energy to a flywheel: NASA uses solar power to energize flywheels in
space.
The equation for rotational KE is shown to the right. The moment of inertia and
maximum angular velocity determine how much energy a flywheel can store. The
moment of inertia, in turn, is a function of the mass and its distance (squared) from the
axis of rotation.
In Concept 1, you see a traditional flywheel. It is large, massive, and constructed with
most of its mass at the outer rim, giving it a large moment of inertia and allowing it to
store large amounts of rotational KE. In Concept 2, you see a modern flywheel, which
is much smaller and less massive, but capable of rotating with a far greater angular
velocity. Flywheels in these systems can rotate at 60,000 revolutions per minute
(6238 rad/s). Air drag and friction losses are greatly reduced by enclosing the flywheel
in a near vacuum and by employing magnetic bearings.
Flywheels
Spinning objects “store” rotational KE
Energy depends on
·angular velocity
·moment of inertia (mass, radius)Flywheels
Serve as mechanical batteries