q_avideo1-3_060122

Good job.

Let me know if there's anything you need me to explain further.

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01:31:41 Physics video clip 01: A ball rolls down a straight inclined ramp. It is the velocity the ball constant? Is the velocity increasing? Is the velocity decreasing?

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RESPONSE --> The ball has an increasing velocity. No the velocity is not contant. It increases in velocity as it moves farther along the ramp.

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01:32:01 If the ball had a speedometer we could tell. What could we measure to determine whether the velocity of the ball is increase or decreasing?

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RESPONSE --> right

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01:34:17 ** STUDENT RESPONSE: By measuring distance and time we could calculate velocity. INSTRUCTOR COMMENTS: The ball could be speeding up or slowing down--all you could get from the calculation you suggest is the average velocity. You could measure the time to travel the first half and the time to travel the second half of the ramp; if the latter is less then we would tend to confirm increasing velocity (though those are still average velocities and we wouldn't get certain proof that the velocity was always increasing). You would need at least two velocities to tell whether velocity is increasing or decreasing. So you would need two sets of distance and time measurements. **

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RESPONSE --> You could actually calcualte the velocity to see if the velocity was increasing or decreasing

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01:34:48 What is the shape of the velocity vs. clock time graph for the motion of the ball?

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RESPONSE --> It is a curves line that is increasing

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01:36:03 ** If the ramp has an increasing slope, the velocity would increase at an increasing rate and the graph would curve upward, increasing at an increasing rate. If the ramp has a decreasing slope, like a hill that gradually levels off, the graph would be increasing but at a decreasing rate. On a straight incline it turns out that the graph would be linear, increasing at a constant rate, though you aren't expected to know this at this point. All of these answers assume an absence of significant frictional forces such as air resistance. **

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RESPONSE --> right. the slope of the line would be increasing because the velocity of the ball is increasing over time.

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01:38:27 A ball rolls down ramp which curves upward at the starting end and otherwise rests on a level table. What is the shape of the velocity vs. clock time graph for the motion of the ball?

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RESPONSE --> The graph would still be increasing over the time interval but the velocity would not be as much.

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01:39:49 ** While on the curved end the ball will be speeding up, and the graph will therefore rise. By the time the ball gets to the level part the velocity will no longer be increasing and the graph will level off; because of friction the graph will actually decrease a bit, along a straight line. As long as the ball is on the ramp the graph will continue on this line until it reaches zero, indicating that the ball eventually stops. In the ideal frictionless situation on an infinite ramp the line just remains level forever. **

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RESPONSE --> so the line would increase while it was on the ramp and then once the ramp stopped and it was level with the table the velocity would not increase anymore and then line on the graph would level off because it would have a constant velocity.

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01:42:05 For the ball on the straight incline, we would certainly agree that the ball's velocity is increasing. Is the velocity increasing at a constant, an increasing, or a decreasing rate? What does the graph of velocity vs. clock time look like?

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RESPONSE --> The velocity is increasing at an increasing rate. the line would be curved upward. AT the begining the line would have a smaller slope but as second went by the slope would increasing which mean the velocity is increasing.

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01:44:09 ** It turns out that on a straight incline the velocity increases at a constant rate, so the graph is a straight line which increases from left to right. Note for future reference that a ball on a constant incline will tend to have a straight-line v vs. t graph; if the ball was on a curved ramp its velocity vs. clock time graph would not be straight, but would deviate from straightness depending on the nature of the curvature (e.g., slope decreasing at increasing rate implies v vs. t graph increasing at increasing rate).**

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RESPONSE --> I don't think that i understand what you mean by straight incline... I thought that like in the experiment that we just did the velocity was increasing at an increasing rate and the incline was straight... I think that I am lost.

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On a straight incline, the velocity is increasing as the ball rolls down it. However as it turns out the increase over, say, every .1 second time interval is the same (or very nearly the same) as the increase over any other .1 second time interval.

Over equal time intervals, the change in velocity is always the same, so we say that velocity increases at a constant rate.

We haven't established that experimentally, we haven't explained it, we haven't proven it, so there is no reason you would be expected to know this right now (though having been told that it's so, you can now regard it as a working assumption). But we will later see why it must be so.