Newton's second law calculator
Force from mass and acceleration, and weight on Earth.
Enter your values and press Calculate. Your inputs stay in the address, so you can switch language or share the link.
Formula
F = m × a W = m × g, g = 9.80665 m/s²
How it works
Newton's second law says the net force equals mass times acceleration. Weight is the force of gravity on a mass: W = m × g with standard gravity g = 9.80665 m/s².
Worked example
The same calculation with the default values:
- Mass 10 kg
- Acceleration 3 m/s²
- F = 10 × 3 = 30 N
- W = 10 × 9.80665 = 98.0665 N
Result: Net force: 30 N · Weight on Earth (standard gravity): 98.0665 N
Uses g = 9.80665 m/s² (standard Earth gravity) for the weight calculation - actual local gravity varies slightly by latitude and altitude, and is completely different on another planet or the Moon.
Common mistakes
- Confusing mass and weight - mass (kg) is constant everywhere, while weight (N) is the force of gravity on that mass and changes with the local gravitational field (e.g. on the Moon).
- Forgetting that F = m × a gives the net force - if multiple forces act on an object, this is their vector sum, not any single applied force.
- Mixing unit systems (e.g. mass in pounds with acceleration in m/s²) - consistent SI units (kg, m/s², N) are required for the result to be physically meaningful.
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