Physics Lab Experiment
Unit 1: Measurement and the Scientific Process
Lab 1: Measuring Speed
Learning goals: Learn how to perform accurate direct and indirect measurements.
Make measurements with stopwatch and meterstick.
Perform basic unit conversions.
Purpose: To observe and measure the speed of an object using different techniques.
Pre-lab Activity:
1. Read the complete procedure. Highlight or underline any section where a measurement must be made. Make note of any section that is confusing and write your questions below.
2. Use the following equation to complete the following problems about speed
a. What is the speed in meters per second of a runner who completes the 100m dash in 10.3s?
b. What is the speed in meters per second of a marathon runner who completes the race in 5 hours and 15 minutes?
c. How far in meters will a car travelling at 65 miles per hour travel as the driver looks away for 1.5 seconds to read a text?
d. How long in hours will it take for a supersonic aircraft (speed = 380m/s) to travel across the Atlantic Ocean (roughly 5600km)?
3. You are given two successive images of a pool table, one taken at exactly 1:55 and 35.3s and the second taken at 1:55 and 35.7s apart. In the first image ball is observed to be 1.03m away from the end of the table and in the second, the ball is observed to be 1.55m away from the end of the table. What is the ball’s average speed between the two images? Show all calculations.
Object 1; The HoverPuck.
This procedure highlights an indirect measurement of speed. The distance travelled and the time elapsed are directly measured and the speed is then calculated from these measurements.
1. In the hallway outside the classroom there are four distances marked by post it notes where you will glide your hoverpuck. Measure the distance between the starting and ending point for each path and record the value.
2. Starting well before the starting point, one member of the group practices pushing the puck at the same initial speed along the marked path. After you are confident with the reproducibility, move on to the next step.
3. Record the time it takes the puck to travel from the starting point to the ending point of each path.
4. Calculate the speed for each path.
Distance traveled (m) / Time Elapsed (s) / Speed (m/s)Object 2; The Closest Indy Car Finish
This procedure highlights an indirect measurement of speed.
5. Open a browser to http://www.youtube.com/watch?v=21dwzbyv19g. Watch the video till the 4:15 mark. You will want to make your measurements near the photofinish part of the video at 3:45. Note: if you have no sound, you will not hear the announcer say that the cars crossed the finish line one thousandth of a second apart.
6. What information do you have to help you determine the speed of these cars at the finish line? Can you determine the speed of the indy car from the video? Why or why not?
7. Indy cars must have a wheelbase of 3.05m. Making whatever measurements are necessary (you will need to put a ruler up to the monitor), determine the speed of the indy car.
8. Make additional measurements to approximate how much time separates each frame of the photo finish images.
Object 3; Pendulum Bob
This procedure highlights both a direct and indirect measurement of speed.
9. Set the pendulum moving. Observe where you expect the fastest motion to occur.
10. A photogate that registers two states: open and blocked. Set the photogate so that the pendulum bob swings through the center of the photogate. Check to make sure that the photogate is blocked when the pendulum hangs straight down.
11. Start the pendulum swinging by pulling it back to an angle of exactly 10 degrees (use a protractor to determine the angle).
12. Push the “Collect” button in LoggerPro to record data. You can stop the data recording after you have several swings recorded.
13. Zoom in on the graph to determine how long the photogate was in its blocked state. Calculate an average blocked time for at least 5 swings.
Trial 1 (s) / Trial 2 (s) / Trial 3 (s) / Trial 4 (s) / Trial 5 (s) / Average14. Measure the width of the pendulum bob. Use this as the distance travelled to calculate the speed of the pendulum bob at the bottom of its motion.
15. The BeeSpi is a modified photogate device that directly measures the speed of an object passing through it. See if you can determine how the BeeSpi works by comparing it to the photogate.
16. Prime the BeeSpi by pushing the button.
17. Release the pendulum from an angle of exactly 10 degrees.
18. Gradually raise the BeeSpi underneath the bottom of the pendulum till the pendulum bob passes through the center of the BeeSpi. A speed measurement in km/hr will appear if done correctly.
19. Average the value of three measurements.
Trial 1 (km/h) / Trial 2 (km/h) / Trial 3 (km/h) / Average (km/h)20. Convert this average value to meters/second and compare it (percent difference) to the value you calculated using an indirect method.
Object 4; Cart on the Track
This procedure highlights an indirect measurement of speed.
21. The sonic ranger is a device that measures the distance between an object and the ranger by sending a pulse and measuring the time till the echo returns (like echolocation of bats or dolphins). Set the ultrasonic ranger at one end of the track and “collect” data with LoggerPro several times to make sure the sensor is aligned properly with the cart.
22. Place the two carts side by side so that the plunger cart can launch the other cart toward the sensor.
23. Press the “Collect” button to log data and, after about 1s of ticking from the ranger, fire the plunger and launch the other cart toward the motion sensor.
24. Examine the data. Choose two points on the graph and collect enough data to calculate the velocity of the car. Hint: the distance travelled must be over the same interval as the time elapsed.
25. Repeat for each of the three plunger settings.
Trial / Initial Time (s) / Initial Position (m) / End Time (s) / End Position (m) / Time Elapsed (s) / Distance Travelled (m) / Speed (m/s)Plunger minimum
Plunger medium
Plunger maximum
26. Make a note of how the graphs recorded in LoggerPro differ from one another.
Lab Questions:
1. With the HoverPuck, how reproducible were your speeds? Calculate the average speed for all four paths. Then calculate the largest percent difference between any single trial and the average speed.
2. Suppose that instead of measuring the separation of the two Indy cars on your computer screen, you’d measured the separation on the screen at the front of the room. The distance you’d measured would be much larger and so would the speed you calculated. What is wrong with this technique and how could you correct it?
3. Why do we average the blocked state time for several different swings for Object 3 (the pendulum) instead of just measuring one?
4. Give two reasons why the two techniques used for Object 3 (the pendulum) might have given different values for the speed of the pendulum. How could each one be “corrected” in a future version of the experiment?
5. Below, sketch the graph recorded by the sonic ranger of the cart launched toward the sensor when the plunger was set to its maximum. Using a dotted line, predict how the graph might change if there was a fourth, even higher setting.