Relativistic Kinetic Energy Calculator

Created by Bogna Szyk
Last updated: Nov 24, 2021

If you're analyzing an object traveling at high speed, you will probably observe that the results provided by our regular kinetic energy calculator are not entirely accurate. In such a case, make sure to use this relativistic kinetic energy calculator that takes into consideration relativistic effects.

What is the kinetic energy?

Kinetic energy, by definition, is the energy resulting from the motion of an object. For example, a car traveling along a highway has certain energy - if it hits another vehicle, the outcome will be much more destructive than if it were moving at 5 mph.

For objects moving at low speeds, you can determine the kinetic energy using the following formula:

KE = 0.5 * m * v²

where:

  • KE is the kinetic energy expressed in Joules,
  • m is the mass ob the object, and
  • v is its speed.

Relativistic effects in measuring the kinetic energy

If the object moves at high velocity - at least 1% of the speed of light - relativistic effects begin to be noticeable. Due to that fact, you can no longer use the simplified formula mentioned in the previous section.

In such a case, you need to calculate the kinetic energy from the famous Einstein's E = mc² equation. This equation describes the total (i.e. both potential and kinetic) energy of the body. To obtain the relativistic kinetic energy, you need to subtract the potential energy (previously found with the potential energy formula) from the total energy:

KE = E - PE

The potential energy, in this case, is equal to the rest mass energy:

PE = m₀c²

KE = mc² - m₀c²

where

  • c stands for the speed of light - a constant equal to 299,792,458 m/s;
  • m₀ is the rest mass of the object.

Rest mass m₀ differs from the regular mass m. m₀ describes the mass of the object at rest - that is, if it's not moving. If the object moves, its true mass increases according to this formula:

m = m₀ / √(1 - v²/c²)

Combining all of these equations, you can derive the relativistic kinetic energy equation:

KE = m₀c² * [√(1 - v²/c²) -1]

Other relativity effects

If you're interested in relativity, check out the velocity addition calculator, too!

Bogna Szyk
Mass
lb
Velocity
mph
Kinetic energy
MJ
People also viewed…

Black Friday

How to get best deals on Black Friday? The struggle is real, let us help you with this Black Friday calculator!

Body fat

Use the body fat calculator to estimate what percentage of your body weight comprises of body fat.

De Broglie wavelength

De Broglie wavelength calculator finds the wavelength corresponding to a particle exhibiting wave-like behavior.
main background