It used to be difficult to take videos, but pretty much everyone has a video camera on their cellphone. Furthermore, most cellphones are even capable of slow motion videos (as fast as 240 frames per second), which is far more technology than what was available just a decade ago. We are going to take advantage of this to use cellphones to record video in order to calculate speeds. We can also use the stopwatch feature to capture even more data.
Equipment List.
A cellphone capable of slow motion video
30 m (100 ft) tape measure
Cones or other markers that can be used to indicate the start and stop of a 25-meter track.
At least one of the following measuring boards:
4 ft x 8 ft plywood with stripes every 25 cm in the long direction (painted stripes, colored duct tape, etc.)
1" x 6" x 8 ft board with stripes every 25 cm (pained stripes, colored duct tape, etc.)
Tennis ball (or other ball that can be thrown safely)
Paper/pen/pencil to write down the times.
Procedure.
The general task is to determine the speed of various objects by either using slow motion video or a stopwatch. The different tasks will be grouped by how they will be measured.
Mark out a 25-meter straight-line course and time the following behaviors with a stopwatch. Each person in the lab group should participate (if possible), and each measurement should be taken three times.
The time it takes for a person to cover the distance while walking at a "normal" pace (whatever feels natural to them).
The time it takes for a person to cover the distance starting from standing still and running as fast as they are comfortable. (Please take care not to injure yourself!)
Set up the measuring board in a safe area. Use the slow-motion video option on the cellphone to capture the object in motion. Your field of view for the camera should around twice as wide as the board. If you are too close, there will be too much distortion of distances due to the gap between the object and the board. If you are too far, you won’t be able to see when the object clears the markings very well.
Throw a ball as fast as you can. It may take several attempts to capture usable footage. The ball should go past at about the same height as the measuring board. The goal is to get three successful attempts. (Try not to damage the phone or the person holding the phone!)
Run past the measuring board at your fastest comfortable speed. (In theory, this should be the same as the 25-meter run.) The measuring board should be about waist level, and you should try to focus on the same part of the body for each measurement.
Example3.5.1.1.Sample Charts.
Table3.5.1.2.25-Meter Walk (in Seconds)
Walk #1
Walk #2
Walk #3
Average Walk
Student A
Student B
Student C
Table3.5.1.3.25-Meter Run (in Seconds)
Run #1
Run #2
Run #3
Average Run
Student A
Student B
Student C
Table3.5.1.4.25-cm Throw (in Frames)
Throw #1
Throw #2
Throw #3
Average Throw
Student A
Student B
Student C
Table3.5.1.5.25-cm Run (in Frames)
Run #1
Run #2
Run #3
Average Run
Student A
Student B
Student C
Discussion.
Explain how you can convert the table of times for the 25-meter walk or run into speed in meters per second. Then convert the values to speed.
The average walking speed for an adult is typically between 1.2 and 1.4 m/s, but there are lots of variables that contribute to this, such as age, height, and individual characteristics. Did anyone in the group walk faster or slower than typical? Was that person aware of this before this lab?
Determine the framerate for the camera that was used for the slow motion footage. How much time does one frame represent?
Convert the average frame count for ball throw into seconds, and then convert those values to speed in meters per second. Organize these values into a table. Which student has the fastest and slowest average speeds? Is there any relevant information that might explain why these individuals’ are what they are?
Convert the average frame count for the run into seconds, and then convert those values to speed in meters per second. Organize these values into a table. Compare these results with the times attained from the 25-meter run. Explain why it should make sense that the 25-meter speed is slower than the 25-cm speed.
Conclusion.
We have explored two methods of measuring speed in this lab. Both methods come down to directly measuring the amount of time required for an object to travel a specific distance, which is the basic definition of the concept of speed. And while speeds were the ultimate result of our calculations, the activity of the lab was more about making measurements. We measured out markers to indicate distances and we used different both a stopwatch and digital video to measure time.
Lab Write-Up Guidance.
Use the following outline to help you write up your lab report completely and correctly.
Title and Header.
What is the title of the lab and who was in the lab group?
Introduction.
In your own words, what was the purpose of the lab activity? This should only take a few sentences for this lab.
Procedure.
This lab had you measuring the amount of time required for a few different types of behaviors. Describe the measurements you took.
Results and Data.
Present your measurements in an organized manner. You can use the sample charts as a guide.
Discussion.
Answer the discussion questions. Be sure that you state the original question and organize it in a way that is easy to follow.
Conclusion.
Write a couple paragraphs about the lab. Did you find anything interesting or surprising? Are there other things whose speeds you might want to measure with the skills you practiced in this lab?
