Navigation
An introduction to the simple math used to measure work.
Imagine pushing against a brick wall until you are sweating and exhausted. Did you actually do any 'work' in the eyes of a scientist? The answer is no—and the reason why is the secret to understanding physics!
Let's say you lift your backpack off the floor. 1. You apply a force of . 2. You lift it a distance of . 3. Use the formula: . 4. The result is Joules.
Quick Check
If you push a heavy car with of force, but the car does not move at all, how much work have you done?
Answer
Zero Joules. Since the distance () is 0, the total work () must also be 0.
When we multiply Newtons by meters, we get a unit called the Joule (). This unit is named after James Prescott Joule, a famous scientist who studied energy. One Joule is equal to the work done when a force of moves an object . To give you an idea of how much that is, lifting a small apple () about one meter into the air is roughly 1 Joule of work. Most everyday tasks, like walking up stairs or pushing a grocery cart, involve hundreds or thousands of Joules!
A dog pulls a sled across the snow. 1. The dog exerts a constant force of . 2. The sled moves a distance of . 3. Calculate the work: . 4. The total work done is .
Quick Check
What is the standard unit used to measure work in physics?
Answer
The Joule ().
For work to be calculated using our formula, the force must be in the same direction as the object's motion. If you are pushing a box forward, only the force moving it forward counts as work. If you carry a heavy box while walking at a constant speed, you are technically not doing work on the box in the direction you are walking, because your upward lift is perpendicular to your forward movement. Physics is picky about direction!
A worker pushes a crate with of force for . Then, they realize it's in the wrong spot and push it back with the same force. 1. First movement: . 2. Second movement: . 3. Total work done: .
Which of the following is the correct formula for work?
How much work is done if you use of force to move a chair ?
If you hold a heavy box perfectly still in your arms, you are doing work on the box according to physics.
Review Tomorrow
Tomorrow morning, try to remember the three letters in the work formula and what units we use for each.
Practice Activity
Find a heavy object at home. Estimate how many Newtons it takes to lift it, measure the height of a table in meters, and calculate the Joules required to lift it onto the table!