To calibrate and use a recording timer to measure short intervals of time.


How could you measure the time it takes for an object to fall from your lab table to the floor? How about the time it takes for the vibrating hammer of an electric bell to make one complete vibration? Such time events are too small to be measured with an ordinary stopwatch. In this experiment, you will measure the period (T) of a recording timer. After calibrating the timer, you will use it to measure the speed and acceleration of a falling body.


The recording timer is a device used for measuring small intervals of time. An electromagnet activates a hammer that vibrates over the same distance in equal periods of time. When a narrow strip of recording tape is passed between a rotating carbon paper disc and the timer, the hammer will make a mark corresponding to one period of vibration. When the tape is pulled through, the distance can be measured in meters from the first dot to the last dot. The distance between any two dots is the distance traveled by the tape during one complete vibration of the hammer. The time of the event can be measured by counting the number of dots and multiplying by the period of the timer. Thus, a distance-time record of the is made.


  1. Each person in your lab group must read every page in this online procedure. Along the way, there will be questions that you must answer.
  2. Designate one person in your group as the Data Recorder. This person should open the Google document Experiment 4 - Measurement of Time for the approved answer template.
  3. When this Google document opens, sign in to your Google account.
  4. From the FILE Menu, choose Make a copy...
  5. From the FILE Menu, choose Rename...and rename the document as follows: Exp 4 - Period (1, 3, 6, or 8) - Group #.
  6. Share this document with the members of your group and with Mr. Skubis at HSTScience@gmail.com.
  7. As a group, answer all questions. Remember to use complete sentences and be mindful of grammar, spelling, and punctuation.
  8. Finally, AS A GROUP write a CONCLUSION as described at the end of this lab. Submit the conclusion on the Google document for full credit.
  9. REMEMBER: **Plagiarism** is a form of **Academic Dishonesty** which carries harsh consequences. DO YOUR OWN WORK!


Part 1 – Calibrating the Timer

  1. Secure the timer to the lab table with a large C-clamp. Plug the timer in and make sure it is in good working condition.
  2. Obtain a fresh carbon paper disc and place it beneath the timer push pin. Place a piece of narrow white recording tape approximately 2 meters long in the timer beneath the carbon paper.
  3. labkin.jpg
  4. One student should hold the start of the tape at his or her side and prepare to walk at a normal steady pace when the timer is activated.
  5. Another student should turn on the timer and using a stopwatch, measure the time it takes for the tape to be pulled through the timer. Record that time.
  6. Count the number of dots starting with the second dot. Ignore any irregularities in the spaces between the dots. Each space represents equal intervals of time regardless of variations in the spaces.
  7. Divide the time by the number of dots to find the period of the timer. Repeat this several times until you have at least 3 trials that are in good agreement with each other.

Part 2 – Speed and Acceleration of a Falling Object

  1. Cut a piece of paper tape that is about 20 cm longer than the distance from the table top to the floor.
  2. To one end of the tape, securely attach a 200-gram mass. Pass the other end through the timer and hold the mass such that it will freely fall to the floor.
  3. Try to minimize the slack in the paper before you drop the mass.
  4. Start the timer and drop the mass to the floor. Stop the timer when the mass hits the floor.
  5. Repeat the procedure using 300-grams and then 400-grams.


  1. Find the period (T) for each trial in Part 1. Again, you should have at least 3 trials that are in good agreement with each other. Calculate the average period. (Show 3 sig figs.)
  2. Using the tape from the 200-gram mass, label the 2nd and 3rd dots A and B, respectively. Count four dots and label the 7th and 8th as C and D, respectively. Repeat this procedure for the remainder of the dots produced before the mass hit the ground.
  3. Measure the distance between A and B, between C and D, etc. Record this data in meters.
  4. Divide the distance A-B by the average period of the timer. Record this as VAB. Repeat this for the other distances.
  5. Now calculate the acceleration for each change in speed. Applying the equation, WordScreenSnapz006.jpg to this experiment, you will obtain
    WordScreenSnapz007.jpg and WordScreenSnapz008.jpg , etc.
  6. Determine the average acceleration, absolute error, and relative error.
  7. Repeat the calculations for the remaining tapes.