Engineering

Question 1

What is inertia?

Answer 1

A measure of how much an object resists a change in velocity.

Question 2

What factors affect moment of inertia?

Answer 2

The total mass and how it is distributed about the axis of rotation.

Question 3

What is the general term for moment of intertia of an object?

Answer 3

I = Σmr²

Question 4

What is the expression for the moment of inertia of:

• a point mass?
• a solid sphere?
• a hollow sphere?
• a solid wheel?
• a circular hoop?

Answer 4

• mr²
• (2/5)mr²
• (2/3)mr²
• (1/2)mr²
• mr²

Question 5

What is a flywheel?

Answer 5

• A heavy wheel with a high moment of intertia (resists changes to rotational motion, as it has a high angular momentum).
• Converts inputted torque into rotational kinetic energy.
• The minimum power needed to overcome frictional torque is inputted to keep flywheel fully ‘charged’. When extra energy is needed, flywheel decelerates, transferring some of its kinetic energy to another part of the machine.

Question 6

What factors affect the energy storage capacity of a flywheel?

Answer 6

• Moment of inertia (therefore mass and shape: mass concentrated away from centre of rotation i.e. spoked or thinner in middle).
• Rotational velocity therefore composite materials used to reduce weight in spokes and provide greater tensile strength to withstand greater centripetal forces & allow higher rotational velocity).
• Torque due to resistance: lubricate bearings, levitate w/ superconducting magnets, spin inside a vacuum.

Question 7

How are flywheels useful in machines with varying loads (give examples of machines)?

Answer 7

They smooth torque and roational speed of components in a machine by decelerating and delivering stored energy to a system when the supplied force drops.

• Potter’s wheel controlled by foot
• Regenerative braking
• Power grids
• Wind trubines
• Riveting machines

Question 8

What are the advantages of using flywheels to store energy?

Answer 8

• V. efficient
• Long life
• Short recharge and discharge time
• Environmentally-friendly

Question 9

What are the disadvantages of using flywheels to store energy?

Answer 9

• They are much larger and heavier than batteries
• Safety risk: wheel could break at high speeds
• Energy lost through friction
• Can oppose changes in direction

Question 10

What is torque?

Answer 10

The turning effect of a force

Question 11

State the law of conservation of angular momentum.

Answer 11

I_initialω_initial = I_finalω_final

Question 12

What conservation law does the ideal gas equation yield for a closed system?

Answer 12

p₁V₁/T₁ = p₂V₂/T₂

Question 13

What quantity is constant in an adiabatic change?

Answer 13

pV^γ

Question 14

What quantity is constant in an isothermal change?

Answer 14

pV

Question 15

What quantity is constant in an isobaric change?

Answer 15

V/T

Question 16

How do the gradients of adiabats and isotherms compare?

Answer 16

The gradients of adiabats are steeper than for isotherms, so the work by a gas expanding adibatically is greater than if it expanded isothermally.