You’ve learned that motion is just a change in position and can be measured by dividing the distance traveled by the time it took to move, or the speed. But what causes motion? What starts you walking down the street or a ball rolling? And what changes motion? Why does a ball thrown up in the air slow down, stop and come back down again?
Watch this animation to find out what causes and changes motion. As you watch the segment, you might want to check the definitions of specific terms. In addition to the glossary words listed above, the term magnitude, and the concepts of unbalanced and balanced forces, will be described.
Stop the animation at any time, watch it again, or read the transcript.
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The earth revolves around the sun, a kicker makes the field goal, and a ball ricochets.
But what makes this change in motion?
Simplified down to its most basic definition: Forces.
A force is a push or a pull that has a magnitude and a direction.
Forces can start motion, when one is bigger than the other, or unbalanced. (kicking a ball)
And forces can also stop or change motion. (ball hitting a wall and bouncing off)
There are all kinds of different forces acting in different ways and directions all the time.
Friction, for instance, is a force between two surfaces that slows movement down.
Gravity is a force that can slow an object down or speed it up, depending on which direction the object is moving. And magnetic force can do the same thing.
Forces are also at play when something is not moving. A ball resting on a table for instance: Both the downward force of gravity, and the upward force of the table are equal. The forces acting upon it are balanced and the ball is not in motion.
And understanding these forces and how they affect the things around us comes in handy, whether you're a physicist, an athlete or an aspiring pool shark.
In the space below write a definition of force. List two things that forces can do. Then list two types of forces.