[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.94,0:00:03.94,Default,,0000,0000,0000,,- [Instructor] An object\Nis moving along a line.
Dialogue: 0,0:00:03.94,0:00:08.94,Default,,0000,0000,0000,,The following graph gives the\Nobject's velocity over time.
Dialogue: 0,0:00:09.04,0:00:11.32,Default,,0000,0000,0000,,For each point on the graph,
Dialogue: 0,0:00:11.32,0:00:15.15,Default,,0000,0000,0000,,is the object moving forward,\Nbackward, or neither?
Dialogue: 0,0:00:15.15,0:00:18.01,Default,,0000,0000,0000,,So pause this video and see\Nif you can figure that out.
Dialogue: 0,0:00:18.01,0:00:19.61,Default,,0000,0000,0000,,All right, now let's do this together.
Dialogue: 0,0:00:19.61,0:00:21.59,Default,,0000,0000,0000,,And so we can see these different points
Dialogue: 0,0:00:21.59,0:00:24.15,Default,,0000,0000,0000,,on this velocity-versus-time graph.
Dialogue: 0,0:00:24.15,0:00:26.80,Default,,0000,0000,0000,,And the important thing to realize is
Dialogue: 0,0:00:26.80,0:00:30.28,Default,,0000,0000,0000,,is if the velocity is\Npositive, we're moving forward.
Dialogue: 0,0:00:30.28,0:00:33.74,Default,,0000,0000,0000,,If the velocity is negative,\Nwe're moving backward.
Dialogue: 0,0:00:33.74,0:00:37.12,Default,,0000,0000,0000,,And if the velocity is\Nzero, we're not moving
Dialogue: 0,0:00:37.12,0:00:39.55,Default,,0000,0000,0000,,either forward nor backwards,
Dialogue: 0,0:00:39.55,0:00:41.75,Default,,0000,0000,0000,,or neither forward nor backwards.
Dialogue: 0,0:00:41.75,0:00:43.62,Default,,0000,0000,0000,,So right over here we see
Dialogue: 0,0:00:43.62,0:00:45.27,Default,,0000,0000,0000,,that our velocity is positive.
Dialogue: 0,0:00:45.27,0:00:47.40,Default,,0000,0000,0000,,It's a positive two meters per second.
Dialogue: 0,0:00:47.40,0:00:51.45,Default,,0000,0000,0000,,So that means that we are moving forward.
Dialogue: 0,0:00:51.45,0:00:54.22,Default,,0000,0000,0000,,Now, over here our velocity\Nis zero meters per second.
Dialogue: 0,0:00:54.22,0:00:56.12,Default,,0000,0000,0000,,So this is neither.
Dialogue: 0,0:00:57.30,0:00:58.83,Default,,0000,0000,0000,,Now, over here our velocity
Dialogue: 0,0:00:58.83,0:01:00.94,Default,,0000,0000,0000,,is negative four meters per second.
Dialogue: 0,0:01:00.94,0:01:01.86,Default,,0000,0000,0000,,So one way to think about it
Dialogue: 0,0:01:01.86,0:01:04.90,Default,,0000,0000,0000,,is we're moving four\Nmeters per second backward.
Dialogue: 0,0:01:04.90,0:01:06.56,Default,,0000,0000,0000,,So I'll write backward.
Dialogue: 0,0:01:07.85,0:01:10.20,Default,,0000,0000,0000,,Now, this is interesting, this last point.
Dialogue: 0,0:01:10.20,0:01:11.19,Default,,0000,0000,0000,,'Cause you might be tempted to say
Dialogue: 0,0:01:11.19,0:01:12.59,Default,,0000,0000,0000,,all right, I'm oscillating.
Dialogue: 0,0:01:12.59,0:01:13.64,Default,,0000,0000,0000,,I'm going up.
Dialogue: 0,0:01:13.64,0:01:15.08,Default,,0000,0000,0000,,Then I'm going down.
Dialogue: 0,0:01:15.08,0:01:16.33,Default,,0000,0000,0000,,Then I'm going back up.
Dialogue: 0,0:01:16.33,0:01:17.75,Default,,0000,0000,0000,,Maybe I'm moving forward here.
Dialogue: 0,0:01:17.75,0:01:20.17,Default,,0000,0000,0000,,But remember, what we're\Nthinking about here,
Dialogue: 0,0:01:20.17,0:01:21.68,Default,,0000,0000,0000,,this isn't position versus time.
Dialogue: 0,0:01:21.68,0:01:23.47,Default,,0000,0000,0000,,This is velocity versus time.
Dialogue: 0,0:01:23.47,0:01:26.35,Default,,0000,0000,0000,,So if our velocity is negative,\Nwe're moving backwards.
Dialogue: 0,0:01:26.35,0:01:30.76,Default,,0000,0000,0000,,And here our velocity is still negative.
Dialogue: 0,0:01:30.76,0:01:33.09,Default,,0000,0000,0000,,It's becoming less negative,\Nbut it's still negative.
Dialogue: 0,0:01:33.09,0:01:35.79,Default,,0000,0000,0000,,So we are still moving,
Dialogue: 0,0:01:35.79,0:01:37.98,Default,,0000,0000,0000,,we are still moving backward.
Dialogue: 0,0:01:37.98,0:01:41.79,Default,,0000,0000,0000,,If we were at this point right\Nover here or at this point,
Dialogue: 0,0:01:41.79,0:01:43.65,Default,,0000,0000,0000,,then we would be moving forward
Dialogue: 0,0:01:43.65,0:01:45.36,Default,,0000,0000,0000,,if our velocity were positive.