In-class exercises:

Exercise 1:  Acceleration of Gravity by Synchronized Pendulum

Work in groups of 4 or 5:

Using one observer to adjust and control the length of the quarter-cycle washer pendulum, another to control the height of the drop and to release the pendulum and the dropped object simultaneously, and two or three other observers to vote on ‘together’ or ‘not together’, take the data necessary to determine the acceleration of gravity.  The second observer  (who releases the two objects) will record the trial number, the pendulum length, the height of the drop, and the ‘yes’ or ‘no’ votes.  This observer will alternate between a number of sheets of paper which is equal to the number of participants in the group, and will distribute these sheets among members of the group.  Each member is then responsible for submitting the information on his or her sheet using the form at http://www.vhcc.edu/dsmith/forms/inclass_experiments_to_be_reported.htm (Physics assts page > bottom, click on link to ‘In-class Experiments to be Reported by Form’ > Data Report for Acceleration of Gravity Experiment 1 .  Be sure to follow instructions accurately.

For homework:

·         Using the information on your sheet and assuming that acceleration of gravity is constant for the object you dropped, make your best estimate of the acceleration of gravity.  Be prepared to report on both your results and on the things you considered in making your estimate.

Exercise 2:  Energy and the rubber band chain.

Read the thermometers at the front of the room to determine the temperature.  Read each thermometer independently and don’t let the reading on one thermometer influence your reading of another.  This means that you need to read the alcohol thermometer in Celsius, the round dial thermometer in Fahrenheit and read the digital temperatures last.

Measure your rubber bands again.  Be very accurate.

Assuming that each domino has a weight of .18 Newton, determine the force exerted by the rubber chain at each measured length.

Between the length measured for 1 domino and the length measured for 3 dominoes:

·         What is the maximum and the minimum force exerted? 

·         Assuming that the force changes linearly with length, what therefore is the average force exerted between these two lengths?

·         What is the change in the length of the rubber band? 

·         How much work is therefore done on the chain as it is stretched from the first length to the second?

·         Your two observations give you two points on a graph of force vs. length.  If you graph these two points, and then (assuming that force is linearly dependent on length) graph a straight line segment between these two points, what is the area beneath this segment, and what is the meaning of this area?

·         What is the slope of this segment, and what is the meaning of this slope?

·         Break the graph into three equal length intervals, and find the area corresponding to each.  What do your results tell you?

For homework:

·         Repeat the above analysis for the interval between 3 and 5 dominoes, again for the interval between 5 and 7 dominoes, and once more for the interval between 7 and 9 dominoes.  However you don’t need to follow the last instruction—i.e., you don’t need to break each interval into 3 sub-intervals. 

·         Use a spreadsheet to verify your results, putting the .18 Newton information into its own cell and using $$ cell reference any time you use the weight of a domino.  This approximate weight might later be modified, and you don’t want to have to change all your calculations.

·         To what degree does your overall graph differ from linear?  How much error do you think might have arisen in your results because of the assumption of linearity?

·         Draw a reasonably accurate graph of force vs. length, confining the length displayed on your graph to the lengths actually observed, and comment on how this graph deviates from linearity.