TFT

Energy Calculator

Calculate kinetic energy (KE = ½mv²) and gravitational potential energy (PE = mgh).

How to Calculate Energy

Step 1: Choose kinetic energy for moving objects or potential energy for raised objects.

Step 2: Enter mass and either velocity (for kinetic) or height (for potential).

Step 3: Click Calculate to see energy in joules plus conversions to kJ, calories, and watt-hours.

Understanding Kinetic and Potential Energy

What Is Energy

Energy is the ability to do work. It comes in many forms - motion, height, heat, electricity - but they all measure in joules. Kinetic energy is what moving objects have. Potential energy is stored energy from position. A roller coaster at the top of a hill has potential energy. As it drops, that becomes kinetic energy.

Kinetic Energy Explained

Kinetic energy depends on two things:

Mass

Double the mass, double the energy. A 2,000 kg car at 60 mph has twice the kinetic energy of a 1,000 kg car at the same speed.

Velocity (squared)

Double the speed, quadruple the energy. That's why high-speed crashes are so much worse. A car at 60 mph has 4x the energy of the same car at 30 mph.

Potential Energy Explained

Gravitational potential energy is simple: lift something up, it gains energy. The formula PE = mgh means mass times gravity times height. On Earth, gravity is 9.81 m/s². On the Moon it's 1.62 m/s² - you'd need to lift something 6 times higher to store the same energy.

Energy Unit Conversions Reference
UnitEquals 1 JouleCommon Use
Joule (J)1 JPhysics, engineering
Kilojoule (kJ)0.001 kJFood energy (outside US)
Calorie (cal)0.239 calChemistry, heat
Kilocalorie (kcal)0.000239 kcalFood energy (Calories)
Watt-hour (Wh)0.000278 WhElectricity, batteries
Kilowatt-hour (kWh)2.78e-7 kWhElectric bills

1 food Calorie (capital C) = 1 kilocalorie = 1,000 calories = 4,184 joules.

Real-World Energy Examples

Kinetic Energy Examples

  • Baseball pitch (100 mph): ~130 J - about the energy in a small bite of food
  • Car at 60 mph (1,500 kg): ~340,000 J - enough to power a 100W bulb for 56 minutes
  • Bullet (9mm, 350 m/s): ~500 J - concentrated in a tiny area, which is why it's destructive
  • Person running (70 kg, 5 m/s): ~875 J - what your body burns in about 10 seconds of sprinting

Potential Energy Examples

  • Phone dropped from 1m: ~1.5 J - not much, but enough to crack a screen
  • Elevator (1,000 kg) at 10 floors: ~300,000 J - regenerated by modern elevators going down
  • Water behind 100m dam (1 kg): ~981 J - hydroelectric plants convert this to electricity
  • Book on 2m shelf (1 kg): ~20 J - harmless until it falls on your foot

Frequently Asked Questions

What is the formula for kinetic energy?
KE = ½mv². Mass in kg, velocity in m/s, result in joules. The velocity is squared, so speed matters more than mass. A small object moving fast can have more energy than a large object moving slow.
How do I calculate potential energy?
PE = mgh. Mass in kg, gravity is 9.81 m/s² on Earth, height in meters. A 1 kg object lifted 1 meter gains about 9.8 joules of potential energy.
What's the difference between joules and calories?
Both measure energy. 1 calorie = 4.184 joules. Food "Calories" (capital C) are actually kilocalories - 1 Calorie = 1,000 calories = 4,184 joules. A 200 Calorie snack bar has 836,800 joules of chemical energy.
Can energy be negative?
Kinetic energy is always positive - you can't have negative motion. Potential energy can be negative depending on your reference point. If ground level is zero, a basement has negative potential energy.
Why does velocity get squared in kinetic energy?
It comes from the work-energy theorem. To accelerate something, you apply force over distance. The faster it's already going, the more distance it covers while you're accelerating it, so more work gets done. The math works out to v².

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