Menu
energy &
simple machines
Work & Machines
The scientific definition of WORK is different from how we use the word every day: in science, work is when an applied force makes an objet move in the same direction as the applied force. So towing a car is work because the applied force and resulting motion are both in the same direction. Lifting a book off the ground is also work: you apply a force upward and the book moves upward. The amount of work depends on both the amount of force aplied and the distance across which the force is applied:
Work is measured in joules (J), force is measured in newtons (N), and distance is measured in meters (m).
To calculate work, we can only input force that is in the same direction of motion, meaning, if you are holding a basket of laundry, you won't be doing work as you walk down the hall, but as soon as you walk up the stairs you are doing work. Why? The force applied to the laundry basket to overcome gravity and pick it up is vertical; when you walk down the hall, the motion of the basket is horizontal (not vertical), so you cannot include the hortizontal distance in your calculation of work. When you walk up the stairs, the force is vertical (because you have to overcome gravity) and the motion is also vertical, so you are doing "work"! |
Sometimes the force is only partially in the direction of motion. For example, if you can't fully carry the trash, you lift up a little as you drag the bag (to ovecome sliding friction), so you apply force in two directions: vertical and horizontal However, because the bag is only moving across the floor, only the amount of force that is applied in the horizontal direction is considered "work."