Free Fall

Mechanics Kinematics Gravity Middle School High School
VELOCITY — TIME time (s) v (m/s) v = g·t DISPLACEMENT — TIME time (s) x (m) x = ½·g·t² SELECT GRAVITY Moon g = 1.6 m/s² Mars g = 3.7 m/s² Earth g = 9.8 m/s² Jupiter g = 24.8 m/s² ground

About

Drop a ball from any height on four different worlds — the Moon, Mars, Earth, or Jupiter — and watch it fall under that body's gravity. As the ball descends, stroboscopic dots mark its position at equal time intervals, making the increasing gaps between dots a visible, intuitive demonstration that the ball is speeding up. Below the canvas, a velocity-vs-time graph and a displacement-vs-time graph update in real time, turning an abstract equation into something you can see building frame by frame.

The stroboscopic trail is the heart of the simulation. Because each dot is separated by the same slice of time, closer dots mean slower motion and wider gaps mean faster motion — no numbers required to read acceleration off the screen. Switching planets instantly changes the gravitational acceleration, so students can directly compare how quickly velocity builds on the Moon (where g is about one-sixth of Earth's) versus on Jupiter (where it is two and a half times stronger).

Learning Goals

  • Describe how velocity changes during free fall and explain why the stroboscopic dot spacing grows over time.
  • Distinguish between the linear velocity-time graph (v = g·t) and the parabolic displacement-time graph (x = ½·g·t²) and explain what the shape of each reveals.
  • Compare gravitational acceleration on the Moon, Mars, Earth, and Jupiter using the graphs and dot patterns as evidence.
  • Predict qualitatively how changing the drop height affects the time of flight and the shape of the graphs without changing their fundamental character.
  • Read specific values from a velocity-time or displacement-time graph to answer quantitative questions about the motion.

How to Use

  • Select a planet from the gravity dropdown to set the gravitational acceleration. Notice the g value updating beside the selector.
  • Drag the Initial Height slider to choose how far the ball will fall (5 m to 130 m). The ball repositions instantly on the canvas.
  • Press Drop! to release the ball. Watch the stroboscopic dots appear — note how the spacing between them grows as the ball accelerates.
  • Observe the two graphs updating in real time: the velocity-time line rises steadily (constant acceleration) while the displacement-time curve bends upward (increasing rate of change).
  • Press Reset, switch to a different planet, and drop again to compare how the ball falls at a different g. Try the Moon and Jupiter back to back for the most dramatic contrast.