# Scientists Say: Momentum

## This word describes a moving object based on its mass, speed and direction

#### Momentum (noun, “moh-MEN-tum”)

This word describes a moving object based on its mass and velocity. An object’s velocity includes both its speed and the direction that it travels. A speeding racecar, a flying kite, a kid cruising along on rollerblades — they all have momentum.

Momentum equals an object’s mass times its velocity. Since velocity has a direction, momentum has a direction too. Imagine a soccer ball soaring down the field toward the goal. The ball’s path makes an arc. As the ball moves toward the goal, it goes up then comes back down. While in motion, friction with the air slows the ball’s speed. The ball’s momentum constantly changes because its speed and direction change. A collision can also change momentum. An athlete kicking that soccer ball transfers momentum from her foot to the ball.

Momentum relates to how difficult it is to stop a moving object. A more massive object has more momentum than a lighter object moving at the same speed. The same amount of force would take longer to stop a bowling ball than to halt the soccer ball. Likewise, faster moving objects also have more momentum. A soccer ball rolling slowly would be easier to stop than one that had just been kicked.

#### In a sentence

Things that rotate, such as hurricanes, have momentum too; it’s called angular momentum.