Force, mass and acceleration in one law.
Newton's second law says F = m times a. Enter any two of force, mass and acceleration and this solves the third, converts it into every common unit, and shows how the force grows as acceleration climbs.
The numbers
Enter mass and acceleration; force is calculated for you.
What the result means
Force grows straight-line with acceleration
Force vs acceleration at your mass
Force scorecard
Force at several accelerations
The same mass pushed at different rates. Force scales in direct proportion to acceleration.
| Acceleration | In g-force | Force (N) | Force (lbf) | Force (kgf) |
|---|
Newton's second law, explained
Understanding Newton's Second Law
Newton's second law states that force equals mass times acceleration (F = ma). A force of one Newton accelerates a one-kilogram mass at one meter per second squared. This law is fundamental to classical mechanics and applies to everything from falling objects to rocket propulsion.
Force Units and Conversions
The SI unit of force is the Newton (N). Other common units include pound-force (lbf, used in the US), dynes (CGS system), and kilonewtons (kN, used in engineering). One Newton equals 0.2248 lbf, 100,000 dynes, or 0.001 kN. Weight is the force of gravity on an object: W = mg.
Common questions
What is a Newton?
A Newton (N) is the SI unit of force. It is the force required to accelerate a 1 kg mass at 1 m/s². An apple weighs roughly 1 Newton. Your body weight in Newtons is your mass in kg multiplied by 9.81.
What is the difference between mass and weight?
Mass is the amount of matter in an object (measured in kg) and does not change with location. Weight is the gravitational force on an object (measured in N) and varies with gravity. On the Moon, you weigh 1/6 as much but your mass stays the same.
Why is 9.81 the default acceleration?
9.81 m/s² is the standard acceleration due to gravity at Earth's surface. It is used to calculate the weight (gravitational force) of objects. The value varies slightly by location (9.78 at the equator to 9.83 at the poles).
Results use classical mechanics at everyday speeds and treat mass as constant. Standard gravity is taken as 9.80665 m/s2. For relativistic speeds, variable mass, or precise engineering work, verify against your own reference values.