Engineering Physics
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- Created by: yasminw24
- Created on: 25-06-17 15:14
What is the formula for angular momentum?
Iw
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When is angular momentum conserved?
Always - provided there are no external torques acting on the system
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What are the units for angular momenutm?
Nms or kgm2/s
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How do you change from rads-1 to revolutons per second?
divide by 2 pi
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What is angular impulse?
It is the change in angular momentum
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What are the units of angular momentum?
Nms
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How does an ice skater spin faster?
They pull their arms in. Like this, she is decreasing her moment of inertia and so her angular velocity must increase in order to conserve angular momentum
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What is Inertia?
The measure of how much an object resists a change in velocity. The larger the inertia, the larger the applied force needed o change its velocity by a given amount
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What is moment of inertia?
The measure of how difficult it is to rotate an object, or to change its rotational speed. It depends on mass and its distance from the axis of rotation
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What are the units for moment of inertia?
kgm2
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How would you calculate the moment of inertia for an extended object?
By adding up the individual moments of inertia of each point mass that makes up the object
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What causes changes in the moment of inertia?
The mass and how it is distributed about the axis of rotation. Also where the object is rotated about
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How would you calculate the moment of Inertia of a bike wheel and a reflector added to the outer edge?
You can add together individual moments of inertia of different objects to find the moment of inertia of the whole system
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What are the units for rotational kinetic energy?
Joules
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What is Torque?
When the force that causes an object to turn, the turning effect is known as Torque
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What is a couple?
A pair of forces which cause no resultant linear motion but which cause an object to turn
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What are flywheels?
A heavy wheel with a high moment of inertia in order to resist changes to its rotational motion - once it is spinning it is hard to make it stop
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What happens when a flywheel spins?
Itis 'charged' as it spins, turning the inputted torque into rotational kinentic energy. Just enought power is continually input to overcoem frictional torque and keep the flywheel fully charged (full of stored energy)
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How does the flywheel transfer some of its kinetic energy?
The flywheel decelerated which transfers some of its kinetic energy to another part of the machine
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What factors affect the energy storage capacity of a flywheel?
Making it heavier, make it spin faster, have a spoked design
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What are flywheel batteries?
Can be used as batteries as they are designed to store as much energy as possible
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How does making a flywheel heavier increase its energy?
Increase moment of inertia which is directly proportional to kinetic energy. so the heavier the wheel the more energy
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How does spinning wheel faster increase its energy?
Energy increases with angular speed squared so increasing speed greatly increases energy
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How does a spoked design increase its energy?
Compared to a solid wheel, a spoked wheel of the same mass stores almost twice as much eneergy as more of its mass is directed towards the outer of the wheel so a larger r
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Why can't we just increase all these properties and create the best ever flywheel?
It begins to become impractical. A giant wheel would take up a lot of space in a machine. Also, increasing angular velocity means the centrifugal force can increase to a point where it starts to break the flywheel apart
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What do most modern flywheels look like?
They're made of carbon fibre to stop them breaking due to the centrifugal force, as although tlihter than steel, it is far stronger and so can be spun much faster
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How do flywheels loose energy due to friction?
From air resistance and the friction between the wheel and the bearing which it spins on
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How do you reduce the effect of friction on flywheels?
1. Lubrication 2. Levitation by superconducting magnets so no contact 3. operate in vacuums or inside sealed cylinders to reduce drag from air resistance
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What real-life examples are there of flywheels?
Potter's Wheel, regernative braking in electric vehciles, power grids, wind turbines, riveting machines: fixing two sheets of material together
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What are the advantages of a flywheel?
They are very effective, they last a long time without degrading, recharge time is short, can react and discharge quickly, environmentally friendly as no chemicals
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What are the disavantages of a flywheel?
Much larger adn heavier than other storage methods e.g. a cell, pose a safety risk if it breaks and protectgice casing needed is extra weight, energy can be lost through friction, if used in moving vehicles they can oppose change in direction
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Other cards in this set
Card 2
Front
When is angular momentum conserved?
Back
Always - provided there are no external torques acting on the system
Card 3
Front
What are the units for angular momenutm?
Back
Card 4
Front
How do you change from rads-1 to revolutons per second?
Back
Card 5
Front
What is angular impulse?
Back
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