Free Fall Calculator
Fall time, distance and impact speed for an object dropped from rest.
What is Free Fall?
Free fall is motion under gravity alone, starting from rest, with air resistance ignored. It is the simplest accelerated motion there is, and both of the textbook questions — how long a fall takes and how far something has fallen — reduce to the same pair of equations.
How it works
Two kinematics equations cover it: h = ½gt² relates distance and time, and v = gt gives the speed reached. Enter the height and the tool solves for the time by rearrangement (t = √(2h ÷ g)); enter the time and it computes the distance directly. Both equations are shown with your numbers substituted, and the impact speed is reported in m/s and km/h because km/h is what makes it feel real.
- Enter what you know. Every field recalculates as you type — there is no submit button. Leave the quantity you want blank and the page solves for it.
- Read the answer and the working. The result appears above the fold; underneath it is the formula with your numbers substituted, so the arithmetic can be checked rather than trusted.
- Check the units and the size. Units are shown on every value and selectable per field, so a result in kJ, kPa or km/h is converted rather than assumed. Sanity-check the magnitude against a known landmark such as 1 g/cm³ for water.
Examples
A textbook problem with a known answer
Every tool here is checked against standard example problems — the molar mass of C6H12O6 is 180.16 g/mol, and free fall from 20 m takes about 2.02 s at g = 9.8 m/s².
A result you want to reason backwards from
Leave the quantity you already know blank instead: given the final answer, most tools recover the starting value — the mass needed for a target concentration, or the height a fall must have had.
Common mistakes
Forgetting that a formula is only as good as its subscripts
H2O and H2O2 are different compounds. The formula field shows its parse — element by element — so a mis-typed subscript is visible before it reaches the arithmetic.
Mixing units in the middle of a calculation
The most common source of a wrong answer is a value in grams next to a formula expecting kilograms, or Celsius next to a gas constant expecting kelvin. This category converts on the way in and labels what it used.
Frequently asked questions
How long does it take to fall 20 m?
About 2.02 s at g = 9.8 m/s², hitting the ground at 19.8 m/s (71 km/h). Load the example to see t = √(2 × 20 ÷ 9.8).
Does the mass of the object matter?
No — not in the absence of air resistance, which is why a hammer and a feather land together on the Moon. On Earth, air resistance makes lighter objects fall more slowly, and this calculator ignores it.
Why is the impact speed so high?
Because speed grows linearly with time but distance grows with the square of time. Falling 20 m takes about two seconds and reaches roughly 20 m/s — around 72 km/h.