Study Guides/Physics/Define 1 Joule of Work
Study Guide · Physics

How to Define 1 Joule (1 J) of Work

In Physics, 'Work' is not just studying or sitting at a desk. Work is strictly defined as an action that happens when a force causes an object to move. The standard SI unit for measuring Work (and Energy) is the Joule (J).

Question (Click to Flip)

If I push a heavy wall with 100 Newtons of force for an hour, but it doesn't move, how much work did I do?

Answer

In physics, you have done Zero Joules of work. Because the displacement (movement) is zero, $W = F \times 0 = 0$. You wasted energy, but no mechanical work was done.

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Key Facts

The Joule is named after the famous English physicist James Prescott Joule.

Because Work and Energy are interchangeable concepts in physics, 1 Joule of Work requires exactly 1 Joule of Energy to perform.

In the CGS system, the unit of work is the Erg. (1 Joule = $10^7$ ergs).

1. The Formula for Work

To define the unit, we must look at the mathematical formula for Work: Work Done (W) = Force (F) $\times$ Displacement (S)

2. Definition of 1 Joule

Using the formula above, if you apply a force of 1 Newton, and the object moves 1 meter, the work done is $1 \times 1 = 1$.

Definition: 1 Joule of work is said to be done when a force of exactly 1 Newton acting on a body moves it by a distance of exactly 1 meter in the direction of the applied force.

3. Example to Understand

Imagine an apple sitting on a table. The apple weighs approximately 100 grams (which means gravity pulls it down with about 1 Newton of force). If you lift that apple straight up exactly 1 meter into the air, you have done approximately 1 Joule of physical work.

Questions and Answers

If I push a heavy wall with 100 Newtons of force for an hour, but it doesn't move, how much work did I do?+

In physics, you have done Zero Joules of work. Because the displacement (movement) is zero, $W = F \times 0 = 0$. You wasted energy, but no mechanical work was done.

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