Force Calculator
Calculate force using Newton's Second Law: F = ma. Enter mass and acceleration to find force in newtons (N), pounds-force (lbf), and kilonewtons (kN).
FORCE
98.1 N
IN lbf
22.0538 lbf
IN kN
0.0981 kN
FORMULA
F = m × a
Force — Reference Table (at g = 9.81 m/s²)
| Mass | Weight (N) | Weight (lbf) |
|---|---|---|
| 0.1 kg | 0.981 N | 0.2205 lbf |
| 1 kg | 9.81 N | 2.2054 lbf |
| 5 kg | 49.05 N | 11.0269 lbf |
| 10 kg | 98.1 N | 22.0538 lbf |
| 50 kg | 490.5 N | 110.2688 lbf |
| 100 kg | 981 N | 220.5376 lbf |
| 500 kg | 4,905 N | 1,102.6881 lbf |
| 1000 kg | 9,810 N | 2,205.3763 lbf |
💡 How to Calculate Force (Newton's Second Law)
What Is Force?
In physics, force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity, meaning it can cause the object to accelerate.
Force can be described as a push or pull upon an object resulting from its interaction with another object, as is the case with gravitational forces. The standard unit of force in the International System of Units (SI) is the Newton (N). One Newton is defined as the force required to accelerate one kilogram of mass at the rate of one meter per second squared.
How to Calculate Force
To calculate force, you need to use Newton's second law of motion. It provides the formula for finding force when the mass and acceleration are known.
Force Formula
Newton's second law states that the force acting on an object is equal to the mass of that object multiplied by its acceleration. This can be expressed mathematically as:
Where:
- F = force (N)
- m = mass of the object (kg)
- a = the object's acceleration (m/s²)
For example, imagine a car with a mass of 1,500 kg accelerating at a rate of 2 meters per second squared. To find the force exerted on the car, plug the values into the formula:
F = 1,500 kg × 2 m/s²
F = 3,000 N
After 5 seconds at this acceleration, the car reaches a velocity of v = 0 + 2 × 5 = 10 m/s (22 mph).
Weight vs. Force
Weight is the gravitational force acting on an object: W = mg. A 70 kg person weighs 70 × 9.81 = 686.7 N (154.3 lbf) on Earth, but only 70 × 1.62 = 113.4 N on the Moon. Mass stays the same; weight changes with the local gravitational acceleration.
Newton's Laws of Motion
Newton's first law, often called the law of inertia, states that an object at rest stays at rest, and an object in motion continues in motion at the same speed and direction unless acted upon by an unbalanced force. Centripetal force is an example of this — it continuously changes the direction of a moving object.
Newton's second law, discussed above, provides the formula F = ma.
Newton's third law states that for every action, there is an equal and opposite reaction. This concept is crucial for finding the normal force exerted on an object by a surface.
Individual Forces vs. Net Force
When multiple forces act on an object, you must find the net force — the vector sum of all individual forces — to determine the object's acceleration. If the net force is zero, the object is in equilibrium. You might also be interested in calculating friction force or spring force.