What’s a *free fall*?


Free fall describes the acceleration of an object exclusively due to gravity. People who jump out of an airplane are slowed by aerodynamic resistance as they fall. A true free fall would only be possible in a vacuum in which no forces other than gravity are able to act.

Is it true that a hippopotamus falls at exactly the same rate as an earthworm in a vacuum?

Build this *Drop Tower*.


You’ll use it to experimentally determine the gravitational constant.

Do a test run.

EV3 Classroom-Programs 2-5-program en-us

Place the model on a solid and level surface. Run the program and wait until the Touch Sensor is shown on the Display. Place the ball in the ball arm and press the Touch Sensor on the back of the Drop Tower to start a drop experiment.

Does the ball land on the Touch Sensor on the bottom of the Drop Tower? Are a big smile and fall time displayed?

Record your results.


Record the experiment number and fall time in a testing table. Make sure to leave enough space for additional columns for further calculations.

Running the Experiment

Keep the following tips in mind as you run your experiment:

  • Ensure that the tower isn’t shaking when releasing the ball.
  • The Touch Sensor can also be held and used as a manual remote control if needed. This allows you to avoid shaking the tower, which might lead to failed experiments.
  • If the experiment was successful, the fall time will be shown on the Display.
  • Perform the experiment at least three times and use the average value to ensure the most reliable results.

Summarize your results.


Use the average measured fall time to calculate the average velocity of the falling ball as well as the acceleration of gravity. If you get stuck, check the “Hint” for the formulas.

What aspect of your ball’s motion changed and what stayed constant?

Velocity Formula

Use the formula below to calculate the average velocity. The displacement is the height of the Drop Tower, which is 50 cm.

v = d / t

v = velocity (m/s)
d = displacement (m)
t = time (s)

Law of Falling Bodies

Use the formula below to calculate the gravitational constant. The displacement is the height of the Drop Tower, which is 50 cm.

d = ½ × g × t²

d = displacement (m)
g = gravitational acceleration (m/s²)
t = time (s)

How did you do?


What did you do well? Is there anything you could’ve done better?

Nice! Now you know how objects accelerate in free fall. Let’s ramp up for the final lesson!