Kinetic Energy Calculator

This kinetic energy calculator lets students, engineers, and enthusiasts compute kinetic energy (KE), mass, or velocity with instant, precise unit conversions. It eliminates guesswork and reduces errors in physics homework, engineering estimates, ballistics baselines, and lab prep.

Data Source and Methodology

Authoritative data source: OpenStax, University Physics Volume 1 — Chapter 7: Work and Kinetic Energy (2016; latest updates online). Direct link: https://openstax.org/details/books/university-physics-volume-1.

Unit definitions and exact conversion factors follow the SI Brochure and NIST references, including: NIST Special Publication 811 and CODATA constants (e.g., 1 lb = 0.45359237 kg; 1 ft = 0.3048 m; 1 eV = 1.602176634×10⁻¹⁹ J; 1 kcal = 4184 J).

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

KE = \frac{1}{2} m v^2
\text{Solving for mass:}\quad m = \frac{2\,KE}{v^2}
\text{Solving for velocity:}\quad v = \sqrt{\frac{2\,KE}{m}}
\text{Momentum:}\quad p = m\,v

These equations assume classical (non‑relativistic) speeds. At relativistic speeds, use KE = (\gamma - 1)mc^2 with \gamma = 1/\sqrt{1 - v^2/c^2}.

Glossary of Variables

  • KE (Kinetic Energy): Energy due to motion. SI unit: joule (J).
  • m (Mass): Amount of matter. SI unit: kilogram (kg). Supported: kg, g, lb, slug.
  • v (Velocity): Speed magnitude. SI unit: meter per second (m/s). Supported: m/s, km/h, mph, ft/s.
  • p (Momentum): Linear momentum, p = m v, SI unit: kg·m/s (equivalent to N·s).
  • Units for energy: J, kJ, MJ, ft·lbf, kcal, eV (conversions shown automatically).
  • Decimal places: Controls rounding of displayed results; internal math uses double precision.

How It Works: A Step‑by‑Step Example

Goal: Compute KE for a 2.5 kg object moving at 12 m/s.

  1. Set “Solve for” to Kinetic Energy (KE).
  2. Enter mass m = 2.5 (unit: kg).
  3. Enter velocity v = 12 (unit: m/s).
  4. Apply the formula: KE = \frac{1}{2} m v^2 = \frac{1}{2} \times 2.5 \times 12^2 = 180\ \text{J}.
  5. Read the conversions: 0.18 kJ, 132.77 ft·lbf, 0.043 kcal.

Frequently Asked Questions (FAQ)

Does the calculator handle different unit systems?

Yes. Enter values in your preferred units. The tool converts to SI internally and then reports results and conversions back to familiar units.

What accuracy should I expect?

All conversions use exact or standards-based factors (e.g., inch and foot are exact in SI). Display rounding is controlled by the Decimal places setting.

Why might my manual result differ slightly?

Differences typically come from rounding at intermediate steps. This tool computes in double precision and rounds only at display time.

What happens if I enter zero or negative values?

Negative mass or energy is invalid and flagged. Zero velocity yields zero KE. For “solve for mass” or “solve for velocity,” velocity must be positive and energy non‑negative.

Is air resistance or gravity considered?

No. The formula calculates pure kinetic energy from mass and speed. It does not include potential energy or dissipative effects.

When should I use relativistic KE?

When speeds approach a significant fraction of the speed of light (say, above 10% of c). This calculator focuses on classical mechanics.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Team.
Last reviewed for accuracy on: .