We want our force of air resistance in pounds of force, so we have to divide by 32.1, numerically equal to the acceleration of Earth's gravity in , to get pounds of force. You just have to know these things. This was a lot of work, but it's over now. Let's calculate a few numbers. We can now show where horsepower comes in.
Horsepower is a measure of power , which is a technical term in physics.
It measures the amount of work that a force does as it acts over time. Work is another technical term in physics. It measures the actual effect of a force in moving an object over a distance. If we move an object one foot by applying a force of one pound, we are said to be doing one foot-pound of work. If it takes us one second to move the object, we have exerted one foot-pound per second of power.