Rotational Dynamics Flashcards
What is the law of conservation of angular momentum?
The total angular momentum in a system remains constant provided that no external TORQUE acts on it
Define Moment of Inertia
It is the measure of the way in which the mass of a body is distributed about its axis of rotation
Define Torque and state it’s unit
It is the turning effect of a force. It’s units are Nm
What is the linear velocity of a rotating object?
Zero
What is a flywheel and how does it work?
It is a heavy wheel with a high moment of inertia. It is ‘charged’ when spun, turning torque into rotational kinetic energy
List some advantages of flywheels
- High efficiency
- Last a long time
- Recharge takes a short time
- They can react and discharge quickly
- They are environmentally friendly
List some disadvantages of flywheels
- They are larger and heavier than other energy sources
- Safety risk as they could break apart at high speeds
- If used in a moving object it can oppose changes in direction
List some uses for flywheels
- Regenerative braking in cars
- Pottery wheels, it helps to supply a constant rotational force from a foot pedal
Torque (net) =
Torque (applied) - Torque (frictional)
How can you reduce friction in a flywheel?
- Lubricate between the bearings and wheel
- Levitate by superconducting magnets so there is no contact between bearings and wheel
- Operate in sealed cylinder to reduce drag from air resistance
What is load torque?
The torque due to resistance forces that a machine must oppose to be useful
What is engine torque?
The torque exerted by the engine
What are the purposes of flywheels?
- They can smooth a system where power is only given intermittently
- They can use spurts of power to charge up, then deliver the energy smoothly to the system.
Energy is always conserved, so the energy lost by masses (mgh) is equal to..
Ek of masses + Rot Ek + T@
Ie - the loss in potential energy of the masses is equal to the kinetic energy of the masses and the wheel, plus the work done to overcome the frictional torque
To keep something turning at a constant velocity, the work done is
T@, or Twt,
Where T is the frictional torque
