course PHY 121
Video Version Experiment 153 Rubber bands:
Good work on most revisions. See my notes on how to get the F * `ds totals and resubmit in the usual manner.
I will of course also be glad to answer questions.
Pullback Prediction Slide Slide * rail N (0.294 N) F of Pullback (0.9 N per cm)
3 cm N/A 1.5 cm 0.444 N 0.9 N
4 cm 2 cm 2.5 cm 0.735 N 1.2 N
5 cm 3 cm 3.5 cm 1.029 N 1.5 N
6 cm 3 cm (1st prediction) 5.0 cm 1.470 N 1.8 N
7 cm 6 cm 6.0 cm 1.764 N 2.1 N
8 cm 7 cm 8.0 cm 2.352 N 2.4 N
9 cm 9 cm 10.0 cm 2.940 N 2.7 N
sliding distance is in cm so the product of sliding distance and frictional force is in cm * N, not in N.
Your rubber band forces now appear to be correct.
It is possible that you read the sliding distance in inches and neglected to convert the inches to cm. Double-check that.
Now to get the F `ds total for each trial answer the following:
How much force was exerted by the rubber bands at the 5 cm pullback position?
How much force was exerted by the rubber bands at the 6 cm pullback position?
What therefore is your best estimate of the average force exerted between these positions?
What is the displacement `ds between these positions?
What therefore is the F_ave * `ds product for the interval between the 5 cm and 6 cm position?
Answer the same for the interval from 0 - 3 cm, then from 3-4 cm, etc..
The total F * `ds for a given position is the sum of all the F_ave * `ds quantities for every interval from 0 cm to that position. For example the F * `ds total for the 5 cm position is the sum of the F_ave * `ds from the 0-3 cm interval, the 3-4 cm interval and the 4-5 cm interval.
4 Rubber bands:
Pullback Prediction Slide Slide * rail N (0.294 N) F of Pullback (0.9 N per cm)
3 cm N/A 2.25 cm 0.662 N 1.35 N
4 cm 4 cm 4.25 cm 1.250 N 1.80 N
5 cm 6 cm 7.00 cm 2.058 N 2.25 N
6 cm 6 cm (1st prediction) 9.00 cm 2.646 N 2.70 N
The forces you give here would be for a series combination of two rubber bands.
However you have a series combination of two parallel combinations, with 2 rubber bands in each.
So your forces will be double what you give here.
I do not understand this experiment. I tried it up to this step:
For each pullback distance determine the force * distance total for the rubber band and for the rail as it slides across the floor.
• For each pullback distance you have the distance the rail slides. Multiply this distance, in cm, by the number of Newtons of force exerted by the rail as it slides across the floor.
• For each cm of pullback, determine the maximum and minimum forces exerted by the rubber band. Average these forces and multiply the average (in Newtons) by the 1 cm distance through which this approximate average force is applied.
I tried to calculate these steps (the last two columns in each table), but do not know if these are right and do not know where to go from here.
Questions you asked me to answer and resubmit:
Are these rubber bands in parallel or in series?
The first rubber bands are in series.
How much is each rubber band stretched if 3 rubber bands in series are stretched a total of 9 cm?
3 cm per rubber band.
How does the tension at the ends of a series of rubber bands compare to the tension in the middle?
I think it would be the same.
How are these rubber bands configured?
The second rubber bands are parallel.
How long is each rubber band when the system is stretched 6 cm?
Each rubber band would be stretched 1.5 cm.
I modified my calculations in the table to correspond with my answers to these questions and my understanding now.
Second resend questions:
The tension in every rubber band would the tension corresponding to a 3 cm stretch, not a 9 cm stretch.
This will reduce all your tensions in the first part be a factor of 3.
I modified the 3 rubber bands table.
I believe the configuration has two rubber bands in parallel, in series with 2 more rubber bands in parallel.
How would this change your results?
The 4 rubber bands were 2 rubber bands in parallel, in series with 2 more rubber bands in parallel. The tension in each of series would be half the total stretch and I modified my 4 rubber band table.