Engineering (mechanics) Flashcards
-what is moment of inertia?
-what is the equation?
-a measure of an objects resistance to being rotationally accelerated about an axis
I=mr²
what does moment of inertia depend on?
- the objects’ total mass
- how it’s mass is distributed about the axis of rotation
what feature does a flywheel have that makes it useful for it’s purpose?
has a large moment of inertia, therefore when rotationally accelerated , it is difficult to stop, and the input torque that causes it to spin is converted into rotational kinetic energy
what are the factors which affect how much energy a flywheel can store?
- mass of flywheel
- angular speed of the flywheel
- friction
- spokes
what are the uses of flywheels?
- regenerative braking in vehicles
- wind turbines
- smoothing torque and angular velocity
what is torque?
equation?
the product of a force and its distance from the axis of rotation
T= Fr
what is angular momentum?
the product of the moment of inertia and angular velocity of an object
what is the law of angular momentum?
the angular momentum of a system remains constant unless acted upon by a external torque
what is angular impulse?
the product of torque and its duration
how can you calculate frictional torque on a wheel experimentally?
- apply an accelerating torque on a wheel to bring it up to a certain velocity
- remove the accelerating torque, and measure the time taken for the wheel to come to rest
- calculate the average deceleration using the equation
- calculate frictional torque using the equation T= Iα
explain why the compression stroke of a diesel engine is considered to be an adiabatic change?
- no heat transfer
- compression stroke is very fast
what is meant by a reversed heat engine?
A device in which an input causes heat transfer from a cold space to a hot space
explain why the coefficient of performance of a reversed heat engine when operating as a heat pump is always greater than the coefficient of performance of the same reversed heat engine when operating as a refrigerator?
Use equations!
COP ₕₚ x W = W + COPᵣₑf x W
COP ₕₚ = 1 + COPᵣₑf
therefore, COP ₕₚ > COPᵣₑf
