Rotational engineering

Question 1

inertia

Answer 1

a measure of how an object resist a change in velocity
larger the inertia, the larger the force applied is needed to be able to change its velocity

Question 2

moment of inertia

Answer 2

measure of how difficult it is to rotate an object or to change its rotational speed
measures resistance to rotation and depends on mass and distance from axis of rotation

Question 3

equation for moments of inertia

Answer 3

I =mr^2

Question 4

moments of inertia
distribution of mass

Answer 4

a hollow object will have a larger moment of inertia to a solid one
e.g. a flywheel has a larger moment of inertia to a wheelbarrow of a similar mass and its more distributed

Question 5

rotational kinetic energy

Answer 5

depends on moment of inertia
Ek = 0.5 I w^2

Question 6

moment of inertia for a solid object

Answer 6

0.5mr^2

Question 7

angular displacement

Answer 7

the angle trough which a point has been rotated

Question 8

angular velocity

Answer 8

a vector quantity
describes the angle a point rotates through per second
w = △θ / △t

Question 9

angular speed

Answer 9

scalar
magnitude of angular velocity

Question 9

angular acceleration

Answer 9

the rate of change of angular velocity
α =△w / △t

Question 10

torque

Answer 10

when a force or couple causes an object to turn
the turning effect is known as torque

Question 10

couple

Answer 10

a pair of forces which cause no resultant linear motion

Question 10

equationS for torque

Answer 10

T = Fr

T = Iα

Question 11

work done and toque

Answer 11

when you rotate an object work is done to make it move
W = Tθ

Question 12

power and torque

Answer 12

power is work done in a given time
P = Tw
w = angular velocity

Question 13

frictional torque

Answer 13

machines with rotating parts will experience an oppsing frictional torque
some of the power of the machine is used to overcome this torque

Question 14

net torque

Answer 14

Tnet = T applied - T frictional

Question 15

flywheel

Answer 15

a heavy wheel with a high moment of inertia in order to resist a changes to its rotational motion`

Question 16

how a flywheels works

Answer 16

flywheels are ‘charged’ when spun turning input torque into rotational kinetic energy
as long as flywheels keeps spinning at this rate it stores energy for later use

Question 17

flywheels and frictional torque

Answer 17

just enough power is continuously put in to overcome frictional torque, keeping flywheels fully charged
when extra energy is needed in other parts of the machine, the flywheel decelerates transferring some of its Ke to other parts of the machine

Question 18

flywheel batteries

Answer 18

flywheels designed to store as much energy as possible

Question 19

factors which effect energy stored

Answer 19

• increase in mass (moment of inertia) hence Ke ∝ m
  -increase in angular speed - energy stored increases with angular speed squared
  -wheel with spokes - mass more concentrated further away from axis of rotation (I)

Question 20

limits on energy capacity

Answer 20

• a gaint heavy wheel, taking too much space is impractical
  -too much angular speed can break the flywheel apart due to centrifugal force

Question 21

what are modern flywheel made of

Answer 21

carbon fibre to allow higher speeds without disintegrating although it is lighter than steel

Question 22

how does flywheels lose some of its energy

Answer 22

flywheels still loses some energy to air resistance and friction between wheel and bearings on which it spinsh

Question 23

how to combat energy loss in flywheel

Answer 23

-lubricate it to reduce friction -leviated with superconducting magnets so there is no contact between bearings and wheel -operate in vacuums or sealed cylindersto reduce drag from air resiatnce

Question 24

load torque

Answer 24

torque due to resistive forcesthat a machine must oppose to be useful

Question 25

uses of flywheels

Answer 25

used in machines to balance or smooth the engine torque and the load torque

Question 26

use of flywheels in systems with a power source that varies

Answer 26

if an engine kicks in intermittently, a flywheel can be used to keep the the angular velocity of any rotating component constant the flywheels uses each spurt of power to charge up it then delivers energy it stored smoothly to rest of the system, instead of bursts

Question 27

if engine torque is higher than load torque

Answer 27

the flywheel will charge up by accelerating so the spare energy is stored until its needed

Question 28

flywheel applications

Answer 28

-vehucles -machines in production process -potter wheel -regenerative braking -power grids -wind turbines

Question 29

regenerative braking

Answer 29

in some electric cars when the brakes are applied the flywheel is engaged the flywheel then charges up with energy that would otherwise be lost when when the vehicle is ready to accelerate, the flywheel uses its energy turn the vehicles wheel faster before being disengaged until needed again

Question 30

potters wheel

Answer 30

powered by a foot pedal, meaning its hard to apply a constant force flywheel used to keep the speed of the wheel constant

Question 31

power grid

Answer 31

when lots of electricity is used in an area, the grid sometimes cannot meet that demand flywheels can be used to store surplus power in times of low demand adn provide extra power when backup power stations are started up in times of high demand

Question 32

wind turbines

Answer 32

flywheels are used to store excess power on windy days or during off-peak times to provide power n days with no wind

Question 33

advantages of flywheels

Answer 33

-very efficient -lasts a long time without disintegrating -recharge time is short -they can react and discharge very quickly -environmentally friendly (dont rely on chemicals)

Question 34

disadvantages of flywheels

Answer 34

-much larger and heavier than other storage methods (batteries) -safety risks, can beeak apart at high speeds. protective casing to protect against this can make it heavier -energy can be lost through friction -if used in moving objects, they can oppsoe changes in direction, which can cause problems for vehicles

Question 35

angular momentum

Answer 35

I w

Question 36

conserbation of angular momentum

Answer 36

always conserved, when no external forces are applied angular momentum is constant I initial x w initial = I final x w final

Question 37

angular momentum ice skater spinning example

Answer 37

at the start of the spin her arms are away from the body when arms are pulled closer, she begins to spin faster due to conservation of angular momentum as she pulls in her arms she decreases her moment of inertia so her angular velocity muct incrase in order to conserve momentum

Question 38

angular impulse

Answer 38

change in angular momentum angular impulse = △(lw)

Question 39

equation f0r angular impulse IF torque on the system remains cosntant

Answer 39

△(Iα) = T△t

Question 43

How to calculate Ep lost

Answer 43

Ek of pulley + Ek mass