How to Calculate Work

By C. Taylor
Applying horizonal force to move a car accomplishes work.
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In physics, "work" is a measurement which quantifies the amount of force used to move an object over a certain distance. For example, to slide a wood block across the garage floor requires some amount of force; the further you slide the block, the more work is involved. If the block never moves, however, no actual work is accomplished, even if you've exhausted yourself in the futile attempt to move it.

Step 1

Calculate the amount of force required to move an object. In the previous example, let's say the block of wood weighs 1,000 newtons (225 pounds). As an aside, a newton is a unit of force -- or in this case, weight -- obtained by multiplying kilograms of mass times meters per second per second of acceleration. The amount of force required to lift the block is simply its weight, but to calculate the horizontal force required to slide it, multiply this weight times the coefficient of friction. Wood on a concrete floor has a coefficient of approximately 0.62, so multiplying 1,000 newtons times 0.62 tells us that the required horizontal force is equal to 620 newtons (139 pounds).

Step 2

Measure the angle of the applied force relative to the horizontal axis. If you were pushing or pulling horizontally, this angle is zero, so the angle doesn't change the force required. If you were pulling up at an angle 30 degrees off the x-axis, however, some of the applied force is wasted, so you need to apply more force to meet the horizontal requirement.

Step 3

Take the cosine of that angle and divide the result into the required horizontal force to calculate the angular force needed. Continuing with the example, the cosine of 30 is 0.87; dividing 620 newtons by 0.87 calculates the amount of angular force required to be 713 newtons (160 pounds).

Step 4

Multiply the result times the distance moved to calculate work. In the example, if you moved the block 10 meters (33 feet), multiply 713 newtons times 10 to calculate the work of 7,130 joules (5,280 foot-pounds). "Joules" describes the amount of work or energy used to apply newtons of force over a distance measured in meters. Similarly, "foot-pounds" describes applying pounds of force over a distance measured in feet.