Physics Tools
What It Does
Works out how far something falls, how long it takes, and how fast it’s going when it lands — from any one of those three — under constant gravity. Pick a planet for its gravity. Everything runs in your browser.
How to Use It
- Enter exactly one of height, fall time, or impact speed.
- Optionally set an initial downward speed (default 0 — dropped from rest) and pick a planet.
- Read the two computed values and the equation for each.
- Click Copy on any computed value, or Copy all to grab every result at once.
About Free Fall
Free fall is motion under gravity alone. Near a planet’s surface the gravitational acceleration g is effectively constant, so a falling object speeds up by g every second. Starting from rest, after a time t it has fallen h = ½gt² and reached a speed v = gt, and these combine into v = √(2gh). A famous and counter-intuitive consequence is that mass doesn’t matter: because heavier objects need proportionally more force to accelerate, everything falls at the same rate in a vacuum — the hammer-and-feather demonstration performed on the Moon. On Earth, g ≈ 9.81 m/s²; on the Moon it’s about a sixth of that, which is why the same drop takes far longer and ends far slower there. This tool ignores air resistance, so it describes a vacuum (or a short, dense-object drop where drag is negligible); real skydivers reach a terminal velocity where drag balances gravity, which is beyond this model. Everything here is computed on your device.
Example
h = 45 m on Earth → t ≈ 3.03 s and v ≈ 29.7 m/s.
Frequently Asked Questions
Does a heavier object fall faster?
No — not in a vacuum. Gravity accelerates every object at the same rate regardless of mass, so a hammer and a feather dropped together land together. Only air resistance makes lighter or less dense objects fall more slowly in everyday life.
Why doesn’t this account for air resistance?
Air resistance depends on an object’s shape, size, and speed, so there is no single simple formula. This tool models ideal free fall in a vacuum, which is accurate for short drops of dense objects and is the standard textbook case.
How do I model a different planet?
Pick a planet from the gravity presets, or type a custom g. The Moon’s gravity is about 1.62 m/s², Mars’s about 3.71 m/s², versus Earth’s 9.81 m/s².
Can I give it an initial speed?
Yes. Leave the initial speed at 0 to drop from rest, or enter a downward speed (for example a ball thrown straight down). Upward throws, which rise and then fall, are better handled by the Projectile Motion or Kinematics (SUVAT) tools.
Is my data sent to a server?
No. Every calculation runs locally in your browser; nothing you enter is transmitted or stored.