Kinetic Energy
Kinetic energy is the energy possessed by an object due to its state of motion. It depends on both the mass of the object and the square of its speed, meaning that doubling the speed quadruples the kinetic energy. Kinetic energy is transferred to objects through work and is a key quantity in collision analysis, transport safety, and the work-energy theorem.
Key Formula
KE = (1/2) × m × v²
LaTeX: KE = \frac{1}{2}mv^2
| Symbol | Meaning | Unit |
|---|---|---|
| KE | Kinetic energy | J (Joule) |
| m | Mass of the object | kg |
| v | Speed of the object | m/s |
Worked Example
Problem
A cricket ball of mass 0.16 kg is bowled at 40 m/s. Calculate its kinetic energy.
Solution
Step 1 — Identify values: m = 0.16 kg, v = 40 m/s. Step 2 — Apply the formula: KE = ½ × m × v² = 0.5 × 0.16 × (40)² = 0.5 × 0.16 × 1600 = 128 J.
Answer
The kinetic energy of the cricket ball is 128 J.
Kinetic energy of a 0.16 kg ball at different speeds
| Speed v (m/s) | Speed (km/h) | Kinetic Energy KE (J) | Relative to 10 m/s |
|---|---|---|---|
| 0 | 0 | 0.00 | 0× |
| 10 | 36 | 8.00 | 1× |
| 20 | 72 | 32.00 | 4× |
| 30 | 108 | 72.00 | 9× |
| 40 | 144 | 128.00 | 16× |
| 50 | 180 | 200.00 | 25× |
Interactive Tools
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Related Terms
Potential Energy
Potential energy is the stored energy possessed by an object due to its position, configuration, or state relative to a reference point or field. Unlike kinetic energy (energy of motion), potential energy is latent and can be converted into kinetic or other forms of energy when the object moves or changes state. The most common forms in classical mechanics are gravitational potential energy and elastic potential energy.
Work (Physics)
In physics, work is done on an object when a force causes a displacement of that object in the direction of the force. Work is a scalar quantity equal to the product of the force, the displacement, and the cosine of the angle between them. It represents the transfer of mechanical energy to or from an object and is measured in joules (J); no work is done if the force is perpendicular to the motion or if there is no displacement.
Conservation of Energy
The law of conservation of energy states that the total energy of an isolated system remains constant over time: energy can neither be created nor destroyed, only transformed from one form to another. In mechanical systems, this means the sum of kinetic energy and potential energy remains constant in the absence of non-conservative forces such as friction. This principle, one of the most fundamental in all of science, is derived mathematically from Noether's theorem as a consequence of the time-translation symmetry of physical laws.
From Greek "kinetikos" (of motion), from "kinein" (to move). The term "kinetic energy" was coined by Lord Kelvin (William Thomson) and Peter Guthrie Tait in their 1867 textbook "Treatise on Natural Philosophy", replacing Leibniz's earlier term "vis viva" (living force). "Energy" itself derives from Greek "energeia" (activity, operation).