Lesson Overview

Learners can:

• define work, and calculate it using the formula W = F x D

• explain how power is related to work

• distinguish between positive work, negative work, and zero work in real-world examples
  
  

Vocabulary

• joule - the unit used to measure energy

• power - the measure of the amount of work that can be done in a given amount of time

• watt - the unit of power

• work - energy transferred to or from an object
  
  

Which of the above tasks seems like more work? Playing basketball, or doing your schoolwork?

You might find schoolwork difficult and playing sports fun, but in science, work is related to force and motion!

​Work

Work is energy transferred to or from an object.

You might think that work is done any time force or energy is used however, scientifically, work only involves using force to move an object.

Additionally, not all work is the same...

​Positive work occurs when the applied force and the object's motion are in the same direction, like lifting a box.

​​Positive Work

​Negative work occurs when the applied force and the object's motion are in opposite directions. Catching or stopping an object involves negative work.

Negative Work

​Carrying an object that has already been lifted is an example of zero work, because the applied force (lifting,) and the direction of movement (walking) are different.

​​Zero Work

​Calculating Work

Work is the product of the force applied and the distance traveled.

Because we are multiplying force and distance, in increase in either factor will increase the amount of work being done.

​Force is measured in Newtons, Distance is measured in meters, and work is measured in a unit called a joule.

Power

The relationship between work being done and the time to complete that work is called power.

Power is calculated by dividing work (in joules) by time (in seconds) and is expressed in a unit called watts.

A watt is a unit of power equivalent to 1 joule of work per second.