Work done by a force

Introduction to Work

In our daily lives, we say we are 'working' when we study for JAMB or carry a heavy bucket of water. But in Physics, if you carry a heavy bag of garri and stand in one spot without moving, you have done zero work. Physics only recognizes work when a force moves something over a distance.

What is Work Done

To do work, you must apply a force, and that force must cause the object to move in the same direction as the force. If you push a broken-down 'danfo' bus and it moves, you have done work. If the bus does not move at all, your work done is zero.

Simply put, work is what happens when you use force to shift an object from one point to another.

The Formula for Work

The mathematical formula for work done is: Work = Force x Distance. We write it as W = F x d. The SI unit for work is the Joule (J). One Joule is the work done when a force of 1 Newton moves an object through a distance of 1 metre.

Work Done at an Angle

Sometimes, you might pull a toy car with a string at an angle. In this case, not all your force is moving the car forward. We use trigonometry to find the part of the force doing the work.

This means if you pull a load at an angle, you multiply the force, the distance, and the cosine of that angle to get the work.

Conditions for Zero Work

There are three times when work done is zero in Physics:

1. When the force is zero (no one is pushing).

2. When the distance is zero (you are pushing a wall that won't move).

3. When the force and the movement are at 90 degrees to each other (like carrying a bucket on your head while walking horizontally).

Worked Example

A student pushes a desk with a force of 50 N through a distance of 4 metres across the classroom floor. Calculate the work done.

1. Write down what you know: Force (F) = 50 N, Distance (d) = 4 m.

2. Write the formula: Work (W) = F x d.

3. Substitute the values: W = 50 x 4.

4. Final Answer: W = 200 Joules (J).