Work and Power

• Define work and power and explain the relationship between them.

• Calculate work and power using their respective formulas and standard units.

• Identify the conditions required for work to be done on an object.

• Describe the purpose of machines and differentiate between simple and compound machines.

• Explain the concepts of efficiency and mechanical advantage in the context of machines.

Key Vocabulary

Work

Work is done when a force causes an object to move over a distance in that force's direction.

Power

Power is the measure of how quickly work is done, or the amount of work per unit time.

Machine

A machine is any device that makes work easier by changing the size or direction of a force.

Mechanical Advantage

Mechanical advantage is how much a machine multiplies input force to produce a larger output force.

Efficiency

Efficiency measures the percentage of work input that a machine converts into useful work output.

What is Work in Physics?

When Work is Done

When There Is No Movement

• No work is done if the object does not move at all.

• This is true no matter how much force you might apply.

• For example, no work is done when pushing on a wall.

Force vs. Movement

• No work is done if force and movement are in different directions.

• For instance, carrying a bag while walking does not count as work.

• The force is up, but the movement is forward.

Calculating Work

What is Power?

What Are Machines?

• A machine makes work easier by changing a force's size or direction.

• Simple machines are basic devices that multiply force to make work easier.

• The six types are the lever, pulley, wheel and axle, wedge, and screw.

• A compound machine combines two or more simple machines to perform a task.

Machine Performance: Input, Output, and Efficiency

• Work input is the work done by the person using the machine.

• Work output is the work done by the machine on an object.

• Efficiency measures how well input work becomes output work, as a percentage.

• A machine's efficiency is always less than 100% due to energy lost from friction.

Actual Mechanical Advantage

Ideal Mechanical Advantage

• ​This is the theoretical mechanical advantage in a perfect system.

• ​​It assumes that there is no friction or any loss of energy.

• ​IMA represents the maximum possible advantage a machine can offer.