berkeley review physics p50; air resistance and standard deviation(help me ;-;)

[tigiyam]

Hi, I am really confused about tbr physics question(part 1) on p50..


(passge is about free falling)
25.
not correcting for wind resistance when evaluating the results of the experiment would lead to a value for gravitational force constant that is too:
A. large. the STD deviation in the raw data would be affected by the presence of wind resistance
B. large. STD deviation in the raw data would not be affected by the presence of wind resistance
C. small. the STD deviation in the raw data would be affected by the presence of wind resistance
D. small.STD deviation in the raw data would not be affected by the presence of wind resistance

answer is D.

I know that it is small, but I can not understand why STD is not affected.
What solution in the back explains is..
"the effect of wind resistance would be uniform across data, because it increases as velocity increases. this means no variation in the standard deviation should be observed beyond that of human error, so rule out choice C in favor of choice D."

I am totally confused here... doesn't the effect of wind resistance increase rather than uniform as the velocity increases??
then.. I think STD also should be changed..

Can someone help me..? ;-;

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[PingPongPro]

I think its because the amount of deviation would be the same in each measurement.

So if the measurement was like 3,4,5,6,7 in actual ideal conditions, but the wind increased it to 5,6,7,8,9 the measurement would change a little, but the deviation is the same. The difference is applied uniformly, if that makes any sense, so the measurements wont deviate any more or less.

It is similar to taking a bunch of measurements with a thermometer that is not calibrated. The values you would measure with such a thermometer would deviate from the actual value if you had used a working thermometer, but standard deviation doesn't change. This is why using a calibrated thermometer isn't that important when you are measuring change in temperatures since you would expect the same amount of error in both measurements.

 

[minombre]

Standard deviation measures the average value of a collection of data's distance from the mean. So if all of the data points changed by the same amount, then the mean would also change by that amount so the average distance from the mean (st dev) would remain unchanged.

Think of a bell shaped curve. The standard deviation basically measures the width of the curve. If you moved the whole thing either to the right or the left (i.e. change all the data points equally), then the width would remain unchanged.

 

[Morsetlis]

Hi, I am really confused about tbr physics question(part 1) on p50..


(passge is about free falling)
25.
not correcting for wind resistance when evaluating the results of the experiment would lead to a value for gravitational force constant that is too:
A. large. the STD deviation in the raw data would be affected by the presence of wind resistance
B. large. STD deviation in the raw data would not be affected by the presence of wind resistance
C. small. the STD deviation in the raw data would be affected by the presence of wind resistance
D. small.STD deviation in the raw data would not be affected by the presence of wind resistance

answer is D.

I know that it is small, but I can not understand why STD is not affected.
What solution in the back explains is..
"the effect of wind resistance would be uniform across data, because it increases as velocity increases. this means no variation in the standard deviation should be observed beyond that of human error, so rule out choice C in favor of choice D."

I am totally confused here... doesn't the effect of wind resistance increase rather than uniform as the velocity increases??
then.. I think STD also should be changed..

Can someone help me..? ;-;

If the wind is resisting the falling of the tree, it falls in slow motion, i.e. the moon, i.e. low gravitational constant. Think of a falling straw versus strip of paper.

Standard deviation measures the normal deviation of a point of data from the mean of data, either in a sample or in the entire population. STD is affected by variation amongst the data, but NOT within the data set. If it were a CHANGING wind, then it would affect the variation within the data sets.