A-LEVEL PHYSICS: 11.1.10: Flywheels in Machines (SaveMyExams) Flashcards
flywheels are used in machines to…
act as an energy reservoir, by storing & supplying energy when required
flywheels consist of…
this means it has:
heavy metal disc/wheel that can rotate rapidly (large moment of Inertia I)
this means it has:
-high mass
-large radius
once flywheels start spinning, it is…
hard to make them stop
flywheels are primarily used in ___ in vehicles where they accumulate and ___ ___
engines, store energy
as a flywheel spins, its input torque is converted into ___ ___ ___, which is…
what is this a result of?
rotational kinetic energy, stored in the flywheel
this is a result of resisting the changes to rotation
the greater the moment of inertia of the flywheel, the greater the…
this means that a ___ shape is preferred over a ___ shape flywheel.
energy stored
wheel, disc
why is a spoked-wheel shape preferred over a disc-shaped flywheel?
greater moment of inertia (I), more energy stored for the same mass
disc: I = 1/2 mr^2
spoked wheel: I = mr^2
why does large rim fitted with spokes help with flywheels?
gives greater moment of inertia for same mass
a flywheel transfers just enough power to a wheel to overcome ___ ___ as it rotates
frictional torque
when more power is needed by the rest of the engine, the flywheel can…
reduce its speed, & transfer more power
flywheels are used to: (2)
-smooth out fluctuations in ω/τ/P
-store rotational kinetic energy
why do engines produce a torque that fluctuates?
power in an engine is not produced continuously, only in the ‘power strokes’ / ‘combustion’ part of an engine cycle
power in an engine is not produced continuously, only in the ‘power strokes’ / ‘combustion’ part of an engine cycle
what does this cause?
this causes an engine to produce a torque that fluctuates
___ makes a flywheel rotate, moving a vehicle forwards
torque
if the ___ on the flywheel is uneven, it will cause a jerky motion to occur in the vehicle. this is a waste of ___.
torque, energy
how do flywheels ‘smoothen’ the jerky motion caused by uneven torque?
they speed up / slow down over a period of time because of its inertia, & as a result, the sharp fluctuations in torque a ‘smoothened’
the greater the moment of inertia of the flywheel, the…
smaller the fluctuation in speed
in conventional braking (eg bikes), the Ek store of the vehicle is transferred as waster through to the ___ ___ ___.
thermal energy store
when regenerative brakes are applied, a ___ is engaged, & will ‘charge up’ by using the energy lost by breaking.
flywheel
when the vehicle needs to accelerate, the ___ stored by the ___ is used to do this
energy, flywheel
KERS:
kinetic energy recovery systems
an ___ ___ in industrial machines can be used along with a flywheel. what is it used for?
electric motor
used to charge up the flywheel, which can then transfer short bursts of energy
factors affecting the energy storage capacity of a flywheel: (4)
-mass
-angular velocity (ω)
-friction
-shape
explain how mass affects the energy storage capacity of a flywheel: (2)
-since I is directly proportional to m, as m increases, I also increases
-rotational kinetic energy is directly proportional to I, so also increases
explain how angular velocity (ω) affects the energy storage capacity of a flywheel: (2)
-rotation kinetic energy is proportional to ω^2
-if ω increases, rotational kinetic energy stored also increases
explain how friction affects the energy storage capacity of a flywheel: (1)
-friction causes energy loss
how can friction in a flywheel be reduced: (3)
-lubricating bearings
-using bearings made of superconductors, so the flywheel can levitate & have no contact
-vacuum to reduce air resistance
explain how the shape affects the energy storage capacity of a flywheel: (1)
-rotational kinetic energy stored depends on the moment of inertia, determined by the shape of the flywheel
