course phy 231 yմآW٤~Ւassignment #002
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19:12:24 How is acceleration an example of a rate of change?
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RESPONSE --> acceleration is the rate of change between 2 measurements. in this case,velocity. confidence assessment: 3
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19:13:15 ** Velocity is the rate of change of position. Acceleration is rate of change of velocity--change in velocity divided by the time period. To find the acceleration from a v vs. t graph you take the rise, which represents the change in the average velocity, and divide by the run, which represents the change in time. The average rate of change of velocity with respect to clock time is the same as the acceleration **
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RESPONSE --> failed to realize time in the average rate of change self critique assessment: 2
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19:14:34 If you know average acceleration and time interval what can you find?
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RESPONSE --> the average velocity would be found confidence assessment: 2
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19:16:57 Can you find velocity from average acceleration and time interval?
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RESPONSE --> no. velocity is found through displacement of an object divided by time confidence assessment: 3
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19:19:27 Can you find change in velocity from average acceleration and time interval?
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RESPONSE --> no. velocity can be found from distance over time confidence assessment: 2
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19:20:52 **Good student response: Yes, the answer that I provided previously is wrong, I didn't consider the 'change in velocity' I only considered the velocity as being the same as the change in velocity and that was not correct. Change in velocity is average accel * `dt. CALCULUS-RELATED ANSWER WITH INSTRUCTOR NOTE(relevant mostly to University Physics students) Yes, you take the integral with respect to time INSTRUCTOR NOTE: That's essentially what you're doing if you multiply average acceleration by time interval. In calculus terms the reason you can't get actual velocity from acceleration information alone is that when you integrate acceleration you get an arbitrary integration constant. You don't have any information in those questions to evaluate c. **
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RESPONSE --> again i forgot about multiplying. notjust dividing. i need to be able to distinguish more between time, distance,velocity, acceleration self critique assessment: 2
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19:21:29 Can you find average velocity from average acceleration and time interval?
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RESPONSE --> yes confidence assessment: 2
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19:22:41 You can find only change in velocity from average acceleration and time interval. To find actual velocity you have to know at what velocity you started. Why can't you find average velocity from acceleration and time interval?
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RESPONSE --> you would more than likely need to know the average acceleration of an object. confidence assessment: 2
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19:24:32 Query Add comments on any surprises or insights you experienced as a result of this assignment.
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RESPONSE --> learned the difference in finding velocity, average velocity, acceleration, time, etc confidence assessment: 3
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You then start the process over with the next question, clicking on the Next Question/Solution button at top left, etc. &#
I just 'clicked through' several questions on the Query and obtained the following SEND file. If you run the program correctly your SEND file will include all this information, plus your answers and self-critiques. ďlɽ٦OH_竫ª}K assignment #002 002. `Query 2 Physics I 01-31-2008 ܺєԧwbzҩ assignment #002 002. `Query 2 Physics I 01-31-2008......!!!!!!!!...................................
00:18:47 NOTE PRELIMINARY TO QUERY:
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RESPONSE -->
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00:18:49 ** Questions about velocity, average velocity, acceleration, etc. are very confusing because so many of the concepts have similar definitions. People have trouble distinguishing things like average velocity, which for uniform acceleration can be obtained in a process that adds two velocities, from average acceleration, which involves subtracting two velocities; one of these processes involves dividing by 2 and the other dividing by the time interval `dt.
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RESPONSE -->
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00:18:52 It is essential to keep the definitions and the meanings of the terms very clear and to work everything from definitions. It is equally important to have a good common-sense understanding of every definition so you can develop the intuition to make sense of everything you do.
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00:18:55 That inevitably takes people a little time. But in the process you develop the habits you will need to succeed in the course. **
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00:18:58 How is acceleration an example of a rate of change?
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RESPONSE --> confidence assessment:
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00:19:02 ** Velocity is the rate of change of position. Acceleration is rate of change of velocity--change in velocity divided by the time period. To find the acceleration from a v vs. t graph you take the rise, which represents the change in the average velocity, and divide by the run, which represents the change in time. The average rate of change of velocity with respect to clock time is the same as the acceleration **
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RESPONSE --> self critique assessment:
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00:19:06 If you know average acceleration and time interval what can you find?
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RESPONSE --> confidence assessment:
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00:19:09 ** Accel = change in vel / change in clock time, so if you know accel and time interval (i.e., change in clock time) you can find change in vel = accel * change in clock time. In this case you don't know anything about how fast the object is traveling. You can only find the change in its velocity. COMMON ERROR (and response): Average acceleration is the average velocity divided by the time (for the change in the average velocity)so you would be able to find the average velocity by multiplying the average acceleration by the change in time. INSTRUCTOR RESPONSE: Acceleration is rate of change of velocity--change in velocity divided by the change in clock time. It is not average velocity / change in clock time. COUNTEREXAMPLE TO COMMON ERROR: Moving at a constant 60 mph for 3 hours, there is no change in velocity so acceleration = rate of change of velocity is zero. However average velocity / change in clock time = 60 mph / (3 hr) = 20 mile / hr^2, which is not zero. This shows that acceleration is not ave vel / change in clock time. COMMON ERROR and response: You can find displacement INSTRUCTOR RESPONSE: From average velocity and time interval you can find displacement. However from average acceleration and time interval you can find only change in velocity. Acceleration is the rate at which velocity changes so average acceleration is change in velocity/change in clock time. From this it follows that change in velocity = acceleration*change in clock time. **
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RESPONSE --> self critique assessment:
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00:19:12 Can you find velocity from average acceleration and time interval?
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RESPONSE --> confidence assessment:
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00:19:16 ** Ave accel = change in vel / change in clock time. If acceleration is constant, then this relationship becomes acceleration = change in velocity/change in clock time. Change in clock time is the time interval, so if we know time interval and acceleration we can find change in velocity = acceleration * change in clock time = acceleration * change in clock time. We cannot find velocity, only change in velocity. We would need additional information (e.g., initial velocity, average velocity or final velocity) to find an actual velocity. For example if we know that the velocity of a car is changing at 2 (mi/hr) / sec then we know that in 5 seconds the speed will change by 2 (mi/hr)/s * 5 s = 10 mi/hr. But we don't know how fast the car is going in the first place, so we have no information about its actual velocity. If this car had originally been going 20 mi/hr, it would have ended up at 30 miles/hr. If it had originally been going 70 mi/hr, it would have ended up at 80 miles/hr. Similarly if an object is accelerating at 30 m/s^2 (i.e., 30 (m/s) / s) for eight seconds, its velocity will change by 30 meters/second^2 * 8 seconds = 240 m/s. Again we don't know what the actual velocity will be because we don't know what velocity the object was originally moving. ANOTHER SOLUTION: The answer is 'No'. You can divide `ds (change in position) by `dt (change in clock time) to get vAve = `ds / `dt. Or you can divide `dv (change in vel) by `dt to get aAve. So from aAve and `dt you can get `dv, the change in v. But you can't get v itself. EXAMPLE: You can find the change in a quantity from a rate and a time interval, but you can't find the actual value of the quantity. For example, accelerating for 2 sec at 3 mph / sec, your velocity changes by 6 mph, but that's all you know. You don't know how fast you were going in the first place. Could be from 5 mph to 12 mph, or 200 mph to 206 mph (hopefully not down the Interstate). COMMON ERROR: Yes. Final velocity is average velocity multiplied by 2. INSTRUCTOR RESPONSE: We aren't given ave velocity and time interval, we're give ave accel and time interval, so this answer is not valid. Note also that final velocity is average velocity multiplied by 2 ONLY when init vel is zero. Be sure you always state it this way. ANOTHER EXAMPLE: You can't find velocity from ave accel and time interval--you can only find change in velocity from this information. For example a velocity change of 10 mph would result from ave accel 2 m/s^2 for 2 seconds; this change could be between 10 and 20 mph or between 180 and 190 mph, and if all we know is ave accel and time interval we couldn't tell the difference. ONE MORE RESPONSE: You can find the change in velocity. The actual velocity cannot be found from ave accel and time interval. For example you would get the same result for acceleration if a car went from 10 mph to 20 mph in 5 sec as you would if it went from 200 mph to 220 mph in 10 sec. **
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RESPONSE --> self critique assessment:
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