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- [Instructor] An object[br]is moving along a line.

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The following graph gives the[br]object's velocity over time.

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For each point on the graph,

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is the object moving forward,[br]backward, or neither?

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So pause this video and see[br]if you can figure that out.

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All right, now let's do this together.

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And so we can see these different points

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on this velocity-versus-time graph.

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And the important thing to realize is

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is if the velocity is[br]positive, we're moving forward.

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If the velocity is negative,[br]we're moving backward.

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And if the velocity is[br]zero, we're not moving

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either forward nor backwards,

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or neither forward nor backwards.

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So right over here we see

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that our velocity is positive.

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It's a positive two meters per second.

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So that means that we are moving forward.

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Now, over here our velocity[br]is zero meters per second.

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So this is neither.

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Now, over here our velocity

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is negative four meters per second.

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So one way to think about it

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is we're moving four[br]meters per second backward.

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So I'll write backward.

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Now, this is interesting, this last point.

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'Cause you might be tempted to say

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all right, I'm oscillating.

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I'm going up.

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Then I'm going down.

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Then I'm going back up.

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Maybe I'm moving forward here.

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But remember, what we're[br]thinking about here,

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this isn't position versus time.

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This is velocity versus time.

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So if our velocity is negative,[br]we're moving backwards.

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And here our velocity is still negative.

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It's becoming less negative,[br]but it's still negative.

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So we are still moving,

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we are still moving backward.

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If we were at this point right[br]over here or at this point,

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then we would be moving forward

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if our velocity were positive.