Machines and Power Transmissions

Question 1

What is a simple machine?

Answer 1

A mechanical device that changes the direction and magnitude of a force.

Question 2

What is a compound machine?

Answer 2

An assemblage of parts that is designed to transmit and transform forces, motion and energy.

Question 3

What is the purpose of a power transmission system?

Answer 3

To move energy from its place of generation to a location where it is applied to perform useful work.
Can be:
Mechanical Power
Electrical Power
Chemical Power.

Question 4

Common Power Transmission Components?

Answer 4

Internal Combustion Engine
Gas Turbine
Steam Engine
Electric Motor

Question 5

Common Transmission Elements?

Answer 5

Gear Sets
Gearboxes and gear trains
Belt drives
Chain Drives

Question 6

Ideal Power Calculations Equations?

Answer 6

In an ideal system, energy is conserved so there is no loss between the input and the output.
Psource = Poutput
P = T x w

Question 7

Non Ideal or realistic Power Equations?

Answer 7

All real systems will dissipate energy.
The Power of the source will always be greater than the power at the output.
Psource > Pout
Pout = Ntrans x Psource
where N is the transmission efficiency which is given by Poutput / Psource
Toutput = Ntrans x T(input) x (wsource / woutput)

Question 8

How do we work out the total Ntrans of a transmission system?

Answer 8

Must take into account all the different efficiencys of all the different components, so things like the gear box and then the chain belt and the bevel gear.

Question 9

How do we work out the speed ratio of a gearbox?

Answer 9

Woutput / Wsource.

Question 10

What is the formula for static friction and when does it occur?

Answer 10

f = Us x N where Us is the static coefficient and N is the normal force. It occurs linearly when there is not enough force to cause motion and rotationally when a wheel roles without slipping.

Question 11

What is the formula for Kinetic Friction and when does it occur?

Answer 11

f = Uk x N, where Uk is the kinetic friction coefficient and N is the normal force. It occurs when there is enough force to make the object move linearly or when a wheel slips.

Question 12

Is Friction a bad thing?

Answer 12

Not always because even though it will take energy away from a system it will often help to provide traction for something like a car.