Open Query 1

course Phy 231

9/05/09xxxx

2 am" "ph1 query 1

*********************************************

Question: `qExplain in your own words how the standard deviation of a set of numbers is calculated.

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

You calculate the mean of the set of numbers, then you get the deviation for each of those numbers (the absolute value of the number minus the mean), then you square the deviations, then you get an average of the squared deviations (well, 'average' qualified by the fact that you divide by one number less than what you have), and then you take the square root of this 'average'.

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

*********************************************

Question: Explain in your own words the process of fitting a straight line to a graph of y vs. x data, and briefly discuss the nature of the uncertainties encountered in the process. For example, you might address the question of how two different people, given the same graph, might obtain different results for the slope and the vertical intercept.

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

You want to fit the data through the lines so that the total vertical distance from the points to the line is minimal. Some people probably estimate the line differently since people probably 'eyeball' the best-fit line differently. If the line is slightly different, the slope and the vertical intercept are also going to be different.

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

*********************************************

Question: Briefly state what you think velocity is and how you think it is an example of a rate.

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

Velocity is the change in distance/change in time, so it is a rate since a rate is defined as quantity A/quantity B (quantity A with respect to quantity B, as velocity is change in distance with respect to time).

Right idea, but to change your wording a bit:

Velocity is the change in position/change in time, so it is a rate since a rate is defined as change in quantity A/ change in quantity B (quantity A with respect to quantity B, as velocity is change in distance with respect to time).

position rather than distance because distance is a positive quantity, whereas position can be positive or negative

the adjective phrase 'change in' is essential to the definition.

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

A rate is a change in something divided by a change in something else.

This question concerns velocity, which is the rate of change of position: change in position divided by change in clock time. **

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

Self-critique (if necessary): OK

*********************************************

Question: Given average speed and time interval how do you find distance moved?

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

Since average speed is change in distance/change in time, you multiply the average speed by that time interval, and that should give you the distance moved.

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

** You multiply average speed * time interval to find distance moved.

For example, 50 miles / hour * 3 hours = 150 miles. **

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

Self-critique (if necessary): OK

*********************************************

Question: Given average speed and distance moved how do you find the corresponding time interval?

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

Since average speed is change in distance/change in time, you divide the distance by the average speed, and that should give you the time interval (since average speed = distance/time, then speed * time = distance, and distance/speed = time).

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

** time interval = distance / average speed. For example if we travel 100 miles at 50 mph it takes 2 hours--we divide the distance by the speed.

In symbols, if `ds = vAve * `dt then `dt = `ds/vAve.

Also note that (cm/s ) / s = cm/s^2, not sec, whereas cm / (cm/s) = cm * s / cm = s, as appropriate in a calculation of `dt. **

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

Self-critique (if necessary): OK

*********************************************

Question: Given time interval and distance moved how do you get average speed?

YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Your solution:

Since average speed is change in distance/change in time, you divide distance/time interval, and that should give you average velocity.

confidence rating: 3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

** Average speed = distance / change in clock time. This is the definition of average speed.

For example if we travel 300 miles in 5 hours we have been traveling at an average speed of 300 miles / 5 hours = 60 miles / hour. **

You have all the right ideas; be sure to see my notes on some of the details of the definition of velocity. You'll understand.