1C30.10 • Measuring g: Freefall Timer (new)

Location: Cabinet 6

Photo shows the demonstration used at the University of Texas at Austin

Concepts Conveyed:

Measuring g.
Investigation of the concept of gravity. Using equations of motion, we can calculate the acceleration due to gravity.
Using the distance between the launch and landing of the marble (y) and the measured time it took to fall (t), we can calculate the acceleration (g) using y = 1⁄2 gt^2

Instructions / Notes:

Ensure the photogate is just below the marble release mechanism and unobstructed. To do this, check that the green light is lit when the photogate system is plugged in.

Note: The calculations for this demo are impacted HEAVILY by even a degree of tilt or a cm or two of distance. To ensure the results are as accurate as possible, load the marble into the release mechanism, then tilt the Gate A sensor until it is red. When the light is red, the sensor’s beam is obstructed. Now, tilt Gate A ever so slightly until the light turns green. This means nothing is obstructing the path of the sensor, but it is now set up so that the time measurements will be as precise as possible; the sensor should now track the motion of the marble as soon as it is released.

The second photogate should be just above the catch basket (the marble’s landing point).
Set the photogate timer to [Interval] mode by pressing the [Mode] button once. NOTE: if your hand passes the Gate A sensor, press [Reset], otherwise the timer will record the passing of your hand as the initial time of the marble.
Squeeze the release mechanism to drop the marble.

NOTE: If the screen shows mangled code, there was an issue with the sensor. Turn the photogate timer OFF, then ON again.

The screen should show a time value for “A-->B” If it only shows the time for A, Gate B’s sensor did not record the marble, and you must rerun the freefall.
The timer records the time it takes for the marble to fall from the release to the bottom photogate.
You may need to repeat the measurement a few times for accuracy. To reset, press the [Reset] button on the timer.
The distance between the start and end point is y = 0.8 m. The most accurate values calculated for g occur when the time measured by the photogate is around 0.403 s. Taking a few measurements and averaging the recorded time gives the best results.
For best results, conduct 5 test trials, then take the average of the results for the value of g.

Demo Staff:

Make sure the removal stick or magnet is included with the demo. The removal stick is used to push the marble up in the basket so it can be easily retrieved.
Ensure that photogate A and photogate B are plugged into port A and port B, respectively.

Last updated on February 18, 2025