Kinetic energy is the energy of an object with mass, due to its motion.
Newton’s law of motion is often used to relate kinetic energy to the product of linear velocity and weight.
A common formula for kinetic energy is E=1/2mv^2 where m is the mass and v is the velocity. Energy can be transferred from one body to another by either applying a force causing a change in speed or by causing an object with static friction to move relative to another static object, transferring kinetic energy in return for potential or internally stored energies that are less than or equal to that particular interaction’s system’s total effective potential energies.
Kinetic energy is also the energy of unbalanced forces exerted on a body in motion. Unlike potential energy, which has many forms and can be stored in many ways, kinetic energy is only present in the form of something moving. Potential and kinetic energy are not interchangeable. The force that causes an object to accelerate is described by Newton’s second law: F=ma, where m is the mass and a is acceleration. The force must be equal to the mass of the object multiplied by its acceleration.
Newton’s second law can be used to measure the energy an object possesses, and the force exerted on an object if it is known. Since kinetic energy is equal to one-half times mass times velocity squared (E=1/2mv^2), and since mass and weight are interchangeable (both are measures of inertia or resistance to change in motion), it is possible to use Newton’s second law to calculate kinetic energy from weight alone. This ability can be useful because weight scales more conveniently than does velocity (v) squared, especially when using large masses and large velocities.
Most common sources of kinetic energy are collisions between two objects, the internal energy of an object due to thermal motions, nuclear reactions occurring inside an atom, and conversions of matter into other forms, such as chemical reactions. The kinetic energy involved in a mass-to-light conversion is derived from the conversion itself.
Kinetic energy is also the energy that would be required to impart an increase in velocity to an object moving at constant speed. For example, suppose a cannon ball is shot straight up in the air with enough force so that it travels upward at 90 m/s. Then suppose that someone holds onto this ball so that it does not fall back down to earth again. If the total force applied to this ball is equal to the weight of the cannon ball (F=mgh), then the kinetic energy of this ball is where “m” is mass, “g” is acceleration due to gravity, and “h” is height. The kinetic energy of an object only depends on the objects speed and not on its mass so once an object reaches a specific constant velocity it will stay there unless acted upon by additional forces.
Practical examples of kinetic energy occur in relation to everyday objects – for example, dropping a stone or hammer or even a pencil. A stone dropped from a building will have its velocity changed by the impact with air resistance followed by gravity.