What is Kinetic Energy?
Kinetic energy is the energy an object possesses due to its motion. In short, it is the energy of movement. Any object that has mass and is moving has kinetic energy. The amount of kinetic energy an object has depends on two factors: its mass and its speed (velocity).
The standard unit for energy is the Joule (J). A Joule is the same unit used to measure work, and this connection is fundamental to physics.
The Kinetic Energy Formula
The formula for calculating kinetic energy is:
- KE: Kinetic Energy, measured in Joules (J).
- m: Mass of the object, measured in kilograms (kg).
- v: Velocity (speed) of the object, measured in meters per second (m/s).
The Importance of Velocity Squared (v²)
The most critical part of the formula is that velocity is squared. This has significant real-world implications:
- Doubling Mass: If you double the mass of an object (e.g., a truck vs. a car at the same speed), you double its kinetic energy.
- Doubling Velocity: If you double the speed of an object (e.g., a car at 60 mph vs. 30 mph), you quadruple its kinetic energy (because $2^2 = 4$).
This squared relationship is why vehicle speed is the most important factor in car crashes. A crash at 60 mph is not twice as bad as one at 30 mph; it involves four times the energy, making it far more destructive.
The Work-Energy Theorem
The Work-Energy Theorem provides the direct link between Work and Kinetic Energy. It states that the net work done on an object is equal to the change in its kinetic energy.
This means if you apply a net force to an object, the work you do (Work = Force × Distance) is converted into kinetic energy, causing the object to speed up. To stop a moving object, you must do negative work on it (e.g., via friction or brakes), which removes its kinetic energy.
- Example: A 10 N force pushes a 2 kg block over 5 meters (assuming no friction). The work done is `W = 10 N × 5 m = 50 J`. This means the block's kinetic energy has increased by 50 J. We can find its final velocity: `50 J = 0.5 × 2 kg × v²`, which means `v² = 50` and `v ≈ 7.07 m/s`.
For a deeper dive, the Wikipedia article on Kinetic Energy is an excellent resource.