Energy, Work, Power

​Mechanical System Efficiency

By Kristen Vezina

Energy cannot be created nor destroyed,
but it can be converted from one form to another.

• Engineers design energy conversion systems to change input energy into a different form of output energy.

• Example: A car engine converts chemical energy (fuel) into mechanical energy (motion).

• In every system, some energy changes into less useful forms because of:

  • Resistance – opposition to the flow of electricity in wires or circuits.

  • Friction – rubbing between surfaces that produces heat.

• These less useful forms of energy are sometimes called energy losses (for example, heat instead of motion).

• To reduce losses, engineers work to improve efficiency – getting the most useful output from the least amount of input.

Multiple Select

What are the two types of energy?

• Cold energy

• Potential energy

• Kinetic energy

• Fast energy

Examples of energy

• Motion

• Electrical

• Thermal

Kinetic

• Gravitational

• Elastic

• Chemical (electrons)

Potential

Efficiency

When energy is converted from one type to another, the goal is to maximize the efficiency of that process.
For example, most electric power plants have an efficiency of around 30%. The rest of the energy is often lost through the smokestack as thermal energy. However, some power plants follow a process called cogenerating(opens in a new tab), where the system captures this thermal energy and uses it to heat a building

Work

Work (symbol W) is the energy transferred when a force, F, is applied to an object moving through a distance, d.
Work is done only by the component of force parallel to the distance the object moves, F_II.

Math Response

A student lifts a 50 pound ball 4 feet. How many ft-lb of work did the student do?

Type answer here

Correct Answer: 200

Deg^°

Rad

Math Response

A student lifts a 50 pound ball 4 feet.

How many joules of work did the student do?

1 ft-lb = 1.35 joules

Type answer here

Correct Answer: 270

Deg^°

Rad

Power

Power (symbol P) is the rate at which work (W) is performed in a given time (t). 
Power is found in various forms: 

• Electrical power uses electrical energy to do work. 

• Mechanical power uses mechanical energy to do work. 

• Fluid power uses energy transferred by liquids (hydraulic) and gases (pneumatic) to do work.

Math Response

A student lifts a 50 pound ball 4 feet in 5 seconds. How much power was used to lift the ball?

Type answer here

Correct Answer: 54

Deg^°

Rad