Force Calculator (F = ma)
Newton's second law solved for force, mass or acceleration.
What is Force?
Newton's second law says the net force on an object equals its mass times its acceleration. It is the bridge between motion and the forces causing it, and the reason one newton is defined as the force that accelerates one kilogram at one metre per second squared.
How it works
F = ma, rearranged for whichever field is blank. Masses in grams or pounds and accelerations in ft/s² or multiples of g are converted to the SI pair of kilograms and m/s² before the multiplication, and the force can be read back in newtons, kilonewtons or pounds-force — so a problem written in imperial units needs no conversion by hand.
- 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
What force accelerates a 10 kg mass at 2 m/s²?
20 N. F = ma = 10 × 2 — load the example and the multiplication appears in the working.
Is weight a force?
Yes. Weight is the gravitational force on a mass, W = mg. A 10 kg mass weighs about 98 N on Earth and about 16 N on the Moon, though its mass is 10 kg in both places.
What is the difference between mass and weight?
Mass is how much matter there is, measured in kilograms and unchanged by location. Weight is the force gravity exerts on that mass, measured in newtons and different on every planet.