## Physics 107 - Comparing and Predicting |

**Comparing and Predicting**

The experiments so far have regularly asked you to make comparisons, and now we are going to take a closer look at how to do this. This experiment starts with two short exercises intended to perfect your skill at comparing measurements with one another. You will begin with the on-paper exercise ‘Bill and Ted’s Excellent Measurement’, followed up by a revisit of the pendulum. The rest of the lab involves collecting some light intensity data and checking a prediction.

**Bill and Ted's Excellent Measurement**

Some students are given a cube marked '52g' and an analog scale, and are asked to determine the mass of the cube.

1. Bill performs five successive measurements of the mass of
the cube and gets the following data: 52.10g, 51.99g, 52.23g,
52.04g, 52.14g. What should Bill write as the mass of the cube?

2. Ted also performs five successive measurements of the mass
the cube and gets the following data: 51.71g, 52.09g, 51.90g,
52.31g, 52.49g. What should Ted write as the mass of the cube?

3. Rufus then also performs five successive measurements of the
mass of the cube and gets the following data: 51.82g, 51.91g,
52.18g, 52.01g, 52.08g. What should Rufus write as the mass of
the cube?

4. Based on your answer, does Bill's answer agree with Ted's?
Why or why not?

5. Based on your answer, does Ted's answer agree with Rufus'?
Why or why not?

6. Based on your answer, does Rufus' answer agree with Bill's?
Why or why not?

7. Whose data is most reliable? Why?

8. Whose data is least reliable? Why?

9. Napoleon then also performs five successive measurements of
the mass of the cube and gets the following data: 51.84g, 52.03g,
51.81g, 52.11g, 51.82g. What should Napoleon write as the mass
of the cube?

10. Based on what you've determined above, comment on Napoleon's
answer.

**Another look at the pendulum period**

You can get greater precision in measuring the pendulum period by
measuring the time for 10 swings and then dividing by 10. That way, the
timing uncertainty, which you know from week 1, gets divided by 10 as
well. Use this improced precsion to measure the pendulum period at 3
different amplitudes (started at 20, 40, and 100cm out from rest). Do
the different amplitudes agree with one another?

**Bright Lights**

1. Take a light meter reading at a distance of 20 cm and then also one at 40 cm to see what factor the reading falls by. Be sure to re-zero the metre between measurments, since the background ligh tvaries a bit with position.

2. Based on these two measurements, make a prediction for the light intensity at 80 cm, and explain how you tried to estimate this.

3. Measure the light intensity at 80 cm and compare to your prediction. Does it agree?

4. For the remainder of the lab, collect a detailed set of measurments of intensity versus distance and plot them.

**Marking Scheme
Bill and Ted's Excellent Measurement
**

1 mark for comparison

4 marks for plotted data set