Collect your data
Have one partner stand next to the measuring tape. Turn on the flashlight and point it upwards. Make sure your flashlight is on a non-blinking setting. Place the light as close to the 0 cm mark as possible and against the measuring tape. If possible, use only one finger to hold the flashlight still until the time of release. Have someone else film the drop with a digital camera (in HD at standard 30 frames per second).
Check your video to make sure you got the shot. Digital video is easy to erase and reshoot. Redo it if you didn’t get a clear view of your flashlight’s light falling straight down. Transfer your video file to a computer.
Record your data
Make a table with two columns to record your data. Label the columns “Time in seconds” and “Distance in meters.” (See the sample table below.)
Time Data: Since your camera records 30 frames a second, each frame represents only 1/30 of a second, or about 0.033 seconds. That means each frame will add an additional 0.033 seconds.
Distance Data: In your video player, find the frame just before your flashlight drops. (Note that frame-by-frame players usually let you move forward or backward via arrow keys. The frame you’re now at is time 0s and distance 0m.)
Now, step by step, record the distance in meters dropped and the corresponding time of the flashlight’s fall. Watch the screen closely. Notice that, during the first few steps, the flashlight doesn’t fall very much.
If your flashlight leaves a streak of light, only record the location at the bottom of the streak (the streak is a 1/30th of a second record of the light's fall).
Calculate the acceleration due to gravity
Acceleration describes how fast the rate of something changes.
Acceleration = (Vfinal – Vinitial) / the time to make this change
Here’s an example using our data (see the table above):
Vinitial is the flashlight’s velocity just before it’s dropped, or 0 m/s; Vfinal is the velocity of the light at the end of the drop.
In our case, at time 0.297 to 0.33 s (time = 0.033 s), the distance traveled is from 0.4 m to 0.51 m (distance = 0.11 m).
V = distance / time
So, Vfinal = 0.11 m / 0.033 s = 3.33 m/s
The time it takes to make that change is 0.33 s
Acceleration = (3.33 m/s – 0 m/s) / 0.33 s = 10 m/s2
Use your own data to calculate the acceleration of the flashlight you drop.
In your own experiments, you can collect data from shorter or longer distances.