Kinetic energy

Moving things have energy.

This is energy of motion. It helps things move.

A fast car has more of it. A slow ball has less.

A woman named Émilie helped explain this.

Energy can change. A person eats food to get energy. Then they use that energy to ride a bike.

Energy can move to other things. A moving ball can hit another ball. The first ball slows down. The second ball starts to move.

Energy is always around us. It is in everything that moves.

Kinetic energy is the energy of motion. Any object that moves has it.

This energy depends on two things. It depends on mass, which is how much matter is in an object. It also depends on speed. If an object goes faster, it has much more kinetic energy. In fact, doubling the speed gives an object four times the energy.

Energy can change from one form to another. A cyclist eats food to get chemical energy. They use that to pedal and gain kinetic energy. If they ride up a hill, that motion turns into gravitational potential energy. This is energy stored by being high up.

Kinetic energy can also move between objects. Think about a game of billiards. When a moving ball hits a still ball, it passes its energy along. The first ball slows down. The second ball starts to move.

Scientists use the joule to measure this energy. Long ago, people called it "vis viva." This is a Latin term for living force. Émilie du Châtelet helped explain how this energy works.

Kinetic energy is the energy of motion. Any object that moves possesses this kind of energy. It is one of many forms of energy in our world. Other forms include chemical energy, thermal energy, and even light. Kinetic energy can be transferred between objects. It can also be transformed into other types of energy.

How does kinetic energy work? It depends on two main things: mass and speed. Mass is how much matter is in an object. Speed is how fast that object is moving. If you double the speed of an object, its kinetic energy actually becomes four times larger. This happens because the energy increases with the square of the speed. You can also see this when a moving ball hits something else. The ball uses its energy to push the other object.

People have studied this idea for a very long time. The word kinetic comes from a Greek word meaning "motion." Long ago, thinkers like Leibniz and Bernoulli called it "vis viva." This is a Latin term for "living force." In 1722, Willem 's Gravesande showed how it works with an experiment. He dropped weights into a block of clay. He found that how deep they went depended on their speed.

Many important people helped us understand these rules. Émilie du Châtelet recognized what Gravesande's experiment really meant. She published an explanation of these ideas. Later, Thomas Young used the word "energy" in a modern way in 1802. In 1829, Gaspard-Gustave Coriolis wrote about the math of kinetic energy. Finally, William Thomson coined the specific term "kinetic energy" around 1849.

We can see kinetic energy in many everyday places. A cyclist uses chemical energy from food to gain speed. This speed is kinetic energy. If the cyclist goes up a hill, that motion turns into gravitational potential energy. When they brake, the kinetic energy turns into heat through friction. Scientists use the joule to measure this energy. You can also find it in spinning objects like flywheels.

Kinetic energy is the form of energy an object possesses because of its motion. It is one of two main classes of energy, the other being potential energy. While energy can exist in many forms, such as chemical, thermal, or nuclear, kinetic energy specifically describes the energy of movement. This energy is not fixed; it can be transferred between objects or transformed into different types of energy.

In classical mechanics, the amount of kinetic energy depends on an object's mass and its speed. For a non-rotating object, the kinetic energy is equal to one-half the product of its mass and the square of its speed. This relationship is expressed by the formula E = 1/2mv². This means that if you double the speed of an object, its kinetic energy does not just double. Instead, it becomes four times larger because the energy increases with the square of the velocity. For example, a car traveling at twice the speed of another requires four times the distance to stop if the braking force remains constant.

Kinetic energy is also deeply connected to the concept of work. The kinetic energy of an object is equal to the work needed to accelerate it from a state of rest to its current speed. Work is defined as the force applied in the direction of motion multiplied by the object's displacement. The same amount of work is required to decelerate that object back to a state of rest. In the International System of Units, energy is measured in joules. In the English system, it is measured in foot-pounds.

We can observe kinetic energy transforming through various processes in daily life. Consider a cyclist who uses chemical energy from food to pedal a bicycle. As they increase their speed, that chemical energy is converted into kinetic energy. If the cyclist coasts up a hill, their kinetic energy is converted into gravitational potential energy. When they apply the brakes, the kinetic energy is dissipated through friction and turned into thermal energy, or heat.

Kinetic energy can also be passed from one object to another during a collision. In a game of billiards, a player uses a cue stick to give kinetic energy to a cue ball. When the cue ball hits another ball, it slows down as its kinetic energy is transferred to the second ball. If the collision is elastic, the kinetic energy is preserved. However, in an inelastic collision, some kinetic energy is lost to other forms, such as sound, heat, or the energy used to break structures.

Understanding kinetic energy has required centuries of scientific discovery. The term "kinetic" comes from the Greek word "kinesis," meaning motion. Early scientists like Gottfried Leibniz and Johann Bernoulli described this force as "vis viva," or living force. In 1722, Willem 's Gravesande provided experimental evidence by dropping weights into clay. He observed that the depth of the impact was proportional to the square of the impact speed.

Émilie du Châtelet was a vital figure in this history, as she recognized the implications of Gravesande's experiments and published an explanation. Later, in 1802, Thomas Young was the first to use the term "energy" in its modern sense. In 1829, Gaspard-Gustave Coriolis published the mathematics regarding the effect of machines. Finally, around 1849, William Thomson, later known as Lord Kelvin, is credited with coining the specific term "kinetic energy."

While classical formulas work for everyday speeds, different rules apply in extreme conditions. If an object moves at a speed comparable to the speed of light, relativistic mechanics must be used instead of classical formulas. Similarly, on an atomic or sub-atomic scale, scientists must use a quantum mechanical model. Kinetic energy also exists in rotating bodies, known as rotational kinetic energy. This is calculated based on the object's moment of inertia and its angular velocity.