Kinetic Energy Calculator
Calculate kinetic energy, momentum, mass, or velocity for a moving object — and see why doubling speed quadruples the energy.
Cómo usar esta calculadora
- 1Choose whether to solve for energy, velocity, or mass.
- 2Enter the two known quantities in SI units — kilograms, metres per second, joules.
- 3Read the result, along with the object's momentum and its speed in km/h and mph.
Cómo funciona
Kinetic energy and momentum
E = ½ × m × v² v = √(2E ÷ m) m = 2E ÷ v² momentum p = m × v energy in joules, mass in kg, velocity in m/s
Kinetic energy is the energy an object carries because it is moving — the work needed to bring it to that speed from rest, or the work it can do in stopping. The velocity term is squared, which is the single most important fact about it: doubling the speed quadruples the energy. Momentum, by contrast, is just mass times velocity and grows linearly, which is why the two quantities behave so differently in collisions.
Ejemplo resuelto
A 1,500 kg car at 100 km/h (27.78 m/s) carries E = ½ × 1500 × 27.78² ≈ 578,875 joules, about 579 kJ. At 200 km/h the same car carries four times as much — over 2.3 million joules — because energy depends on the square of the speed.
Kinetic Energy Calculator: la guía completa
Why the velocity is squared
Kinetic energy is ½mv², and that squared velocity is what makes speed so consequential. Doubling an object's speed does not double its energy — it quadruples it. Tripling the speed multiplies the energy ninefold. This is not an abstract mathematical detail; it is the reason a modest increase in speed produces a dramatic increase in danger.
Braking distance is the clearest illustration. Stopping a vehicle means removing all its kinetic energy through the brakes, and since that energy grows with the square of speed, so does the distance needed to shed it. A car going twice as fast needs roughly four times the distance to stop — the physics of why speed limits matter so much.
Energy versus momentum
Kinetic energy and momentum are both measures of motion, but they behave differently and answer different questions. Momentum (mass times velocity) is conserved in every collision and determines how motion is shared between objects that hit each other. Kinetic energy determines how much damage is done, and in most collisions some of it is lost — converted to heat, sound, and deformation.
The squared-versus-linear distinction is what separates them. A heavy, slow truck and a light, fast bullet can carry the same momentum, but the bullet, with its far higher speed, carries vastly more kinetic energy. This is why momentum tells you which way the wreckage moves after a crash, while energy tells you how badly things are mangled.
Where the energy goes
Kinetic energy is never destroyed, only transformed. When a car brakes, its energy becomes heat in the brake discs. When a hammer strikes a nail, it becomes the work of driving the nail plus heat and sound. When a meteor hits the atmosphere, its enormous kinetic energy becomes the light and heat of a fireball. Tracking where the energy goes is the heart of understanding any mechanical process.
This conservation is also what makes the calculation so useful in reverse. Knowing the energy released in an impact, you can work back to the speed involved, which is how crash investigators reconstruct accidents and how physicists infer the velocity of particles from the energy they deposit in a detector.
Preguntas frecuentes
What is the kinetic energy formula?
E = ½ × m × v², where m is mass in kilograms and v is velocity in metres per second, giving energy in joules. The velocity is squared, so kinetic energy is far more sensitive to speed than to mass.
Why does doubling my speed quadruple my energy?
Because kinetic energy depends on velocity squared. Doubling v multiplies v² by four, so the energy quadruples even though the speed only doubled. This is why braking distance grows so steeply with speed and why high-speed collisions are disproportionately severe.
What is the difference between kinetic energy and momentum?
Momentum is mass × velocity and grows linearly with speed; kinetic energy is ½ × mass × velocity² and grows with the square of speed. Momentum is conserved in all collisions and sets how motion is shared; energy determines how much damage is done and is often partly lost to heat.
Can kinetic energy be negative?
No. Mass is always positive and velocity is squared, so kinetic energy is always zero or positive. An object at rest has zero kinetic energy; any motion gives it a positive value. Only potential energy can be negative, depending on the reference point chosen.