Energy is generally defined as a physical quantity that describes the capacity for doing physical work. Energy cannot be created or destroyed, but can be transferred from one type to another. Among the nine types of energy are potential energy, thermal energy and kinetic energy. Kinetic energy is associated with the movement of an object, and it has implications in our everyday lives.
Kinetic energy is the type of energy associated with the movement of an object. The amount of kinetic energy that a macroscopic, non-rotating body possesses can be quantified with the following equation:
kinetic energy = 0.5 x mass x (velocity)^2
In words, the kinetic energy is equal to half the mass multiplied by the velocity squared. For example, if a car traveling on the highway has a mass of 1,000 kg and speed 96 kilometers per hour (60 miles per hour), then its kinetic energy is equal to 354 kilo-Joules. This is just one hundred-billionth of the energy unleashed in a 1 megaton nuclear explosion.
Increasing the Mass of an Object
Increasing the mass of an object is one means to increase its kinetic energy. The equation for kinetic energy shows that increasing the mass of an object by 10 times increases the kinetic energy by a factor of 10. Following the example of the car on the road, if the car's mass is increased to 10,000 kg, then its kinetic energy is equal to 3,540 kilo-Joules. The kinetic energy dependence explains why objects of higher mass, such as trucks, produce more devastation in road traffic accidents.
Increasing the Velocity of an Object
Increasing the velocity of an object is the second means of increasing kinetic energy. The equation for kinetic energy shows that increasing the velocity by a factor of 2, increases the kinetic energy by a factor of 4. Since the velocity is squared, this term has more significance. Following the example of the car on the road with mass 1,000 kg, if the car's velocity increases by a factor of 2, then its kinetic energy is increased to 1,416 kilo-Joules. The dependence of the kinetic energy on velocity demonstrates why faster vehicles cause more damage in a road traffic accident.
Case Study: The Chelyabinsk Meteor
On the Feb. 15, 2013, the city of Chelyabinsk was home to a cosmic disaster. A meteor of mass 12,000 tons and velocity 19 kilometers per second exploded above the city at an altitude approximately 45 kilometers. The huge mass and velocity meant that the meteor had a massive kinetic energy, equivalent to 30 Hiroshima atomic bombs. Thankfully, the vast majority of the kinetic energy was absorbed by the atmosphere.
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