3) Flywheels

Question 1

Explain the basic features of wheel design which would lead to a low moment of inertia about the axis of rotation.

Answer 1

-For a low I, low density materials are needed of high strength e.g. carbon fibre.
-For low I, small radius helps, but limited by design
needs.
-So low I if most of the mass is near axle, and little mass far from the axle.
-Hence use narrow tyres, low mass rims and tyres, spoke
tensioners at the hub.

Question 2

What 2 things is Ek proportional to?

Answer 2

ω^2 and I.

Question 3

Describe how a flywheels shape can be modified to

store more energy.

Answer 3

• I depends on the mass and distribution of mass around axis.
• I = Σmr^2 so arrange more mass at the outer edge of the flywheel by using heavy rim and spokes.
• Increase thickness to increase m/I.

Question 4

How can the material from which a flywheel is made be modified to store more energy?

Answer 4

• Use a higher density material.

- Gives greater mass for a given size.

Question 5

How can the mechanism of a flywheel be modified to store more energy?

Answer 5

Use lubrication or roller bearings to reduce friction at bearings.

Question 6

State one function of a flywheel.

Answer 6

to store rotational kinetic energy.

Question 7

Describe and explain some of the design features of a flywheel in order for it to store maximum energy.

Answer 7

-Energy stored depends on the moment of inertia and ω^2.
-Importance of shape; put more m at greater r, use thin axle.
-Friction reduced by low-friction bearings and smooth
outer surface.
-Rotational speed limited by tensile strength of material.
-Frictional torque increases with rotational speed.