When you apply a force to an object that's free to move, it begins to accelerate, and the amount of acceleration depends in part on the size of the force, measured in newtons. The other relevant factor is the body's mass, which is a measure of its resistance to force. The acceleration determines the object's final speed in meters per second. The longer the body accelerates, the greater its final velocity measured in meters per second.

Divide the force, in newtons, by the object's mass, in kilograms, to find its acceleration. If a force of 1,000 newtons, for instance, moves a mass of 100 kilograms, then its acceleration is 1,000 / 100 = 10 meters per second squared.

Multiply the acceleration by the time the body spends accelerating. If it accelerates, for instance, for 5 seconds, then 10 x 5 = 50 meters per second.

Add the increase in velocity to the the object's initial speed. If it starts, for instance, at 30 meters per second, then 30 + 50 = 80 meters per second. This is the body's final speed.

#### Tip

The force of friction usually opposes the force causing the motion, and the force of gravity may act in opposition or in addition to the force causing the motion. In real systems, you need to take both friction and gravity into account. Acceleration due to gravity on Earth is a constant 9.8 meters per second squared.