Physics
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Kinetic Energy Calculator.
Calculate classical kinetic energy and momentum from mass and speed.
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Results update as you type.
How to Use
Kinetic energy is KE = ½ × mass × speed². Enter kilograms and metres per second for joules.
This is the classical formula. At speeds close to the speed of light, relativistic mechanics is required.
FAQs
What is the kinetic energy formula?
Classical kinetic energy is KE = ½ × m × v², where m is mass in kilograms and v is speed in metres per second. The result is measured in joules.
What units does this calculator use?
Enter mass in kilograms and speed in metres per second. The calculator returns energy in joules and momentum in kilogram-metres per second.
Does this work at near-light speeds?
No. This tool uses the classical approximation. Relativistic kinetic energy is required when an object's speed is a meaningful fraction of the speed of light.
How to Use the Kinetic Energy Calculator
Enter an object's mass and speed to calculate its classical kinetic energy and momentum.
- Enter the mass in kilograms.
- Enter the speed in metres per second.
- Read the energy in joules and momentum in kilogram-metres per second.
Kinetic Energy Formula
Classical translational kinetic energy depends linearly on mass and quadratically on speed.
Kinetic energy
Multiply one half by mass in kilograms and speed in metres per second squared.
Example:
Input: Mass: 10 kg, speed: 3 m/s
Calculation: ½ × 10 × 3²
Result: 45 J
Momentum
Momentum is mass multiplied by velocity; this calculator uses the entered speed for its magnitude.
Example:
Input: Mass: 10 kg, speed: 3 m/s
Calculation: 10 × 3
Result: 30 kg·m/s
Common Use Cases
Use the result to check introductory mechanics, motion, and energy calculations.
Physics study
Verify a classical mechanics exercise while keeping the units explicit.
Motion comparisons
Compare how changing mass or speed changes an object's energy.
Assumptions and Limitations
Tips
- Use kilograms and metres per second for the displayed SI result.
- Doubling mass doubles kinetic energy; doubling speed multiplies it by four.
- The formula is classical and does not model relativistic speeds.
Common Mistakes to Avoid
- Using velocity squared without converting the speed to metres per second.
- Confusing kinetic energy in joules with momentum in kilogram-metres per second.
Related Resources
Related Calculators
Cite this calculator
Canonical URL: https://mathify.one/en/physics/kinetic-energy
Cite as: Mathify. (2026). Kinetic Energy Calculator. https://mathify.one/en/physics/kinetic-energy
Use Cases
Physics Homework and Exam Prep
Quickly verify your manual calculations for kinetic energy and momentum problems in classical mechanics.
Example: Check the KE of a 2 kg object moving at 3 m/s: KE = 0.5 × 2 × 9 = 9 J.
Engineering and Design Estimates
Estimate the kinetic energy of moving parts or vehicles to assess impact forces or energy requirements.
Example: Estimate the KE of a 1500 kg car at 20 m/s: KE = 0.5 × 1500 × 400 = 300,000 J.
Frequently Asked Questions
- How do I calculate kinetic energy with this calculator?
- Enter the mass in kilograms and the speed in metres per second. The calculator applies the formula KE = ½ × mass × speed² to give you the kinetic energy in joules. It also computes momentum as mass × speed.
- What units does the calculator use?
- Mass must be entered in kilograms (kg) and speed in metres per second (m/s). The kinetic energy result is given in joules (J), and momentum in kilogram metres per second (kg·m/s).
- Can I use this for relativistic speeds?
- No, this calculator uses the classical formula KE = ½mv², which is accurate for speeds much less than the speed of light. For relativistic speeds, a different formula is required.
Tips & Common Mistakes
Tips
- Ensure mass is in kilograms and speed in metres per second to get results in joules and kg·m/s.
- Remember that kinetic energy scales with the square of speed – doubling speed quadruples KE.
- Use the momentum result for collision problems; it's calculated as mass × speed.
- For rough estimates, you can round speed to the nearest whole number, but for precise work use exact values.
Common Mistakes to Avoid
- Entering mass in grams or speed in km/h without converting to kg and m/s – this gives incorrect results.
- Forgetting to square the speed in the KE formula – a common error that leads to half the correct value.
- Using the calculator for relativistic speeds where classical KE is not accurate.
Last updated: August 13, 2026