Energy and Momentum
Learn about the different forms of energy and how they transform
Energy is what makes things happen — it makes things move, glow, get warm, or make sound. It can’t be made or destroyed, only changed from one kind into another.
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Energy is the ability to do work or cause change. It exists in many forms, including kinetic, potential, thermal, chemical, and electromagnetic.
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The law of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another.
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Momentum is the product of an object's mass and velocity. Like energy, momentum is conserved in closed systems.
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When objects collide, both energy and momentum are conserved, though energy may change forms (e.g., from kinetic to thermal).
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Power is the rate at which energy is transferred or work is done, measured in watts (joules per second).
The Conservation Principles
The concepts of energy and momentum conservation have deep historical roots. In the 17th century, Gottfried Leibniz introduced the concept of 'vis viva' (living force), an early version of kinetic energy. Later, scientists like James Joule demonstrated that different forms of energy (mechanical, electrical, thermal) could be converted into one another. By the 19th century, the law of conservation of energy was firmly established as one of physics' most fundamental principles, later expanded by Einstein's famous equation E=mc², which showed that even mass is a form of energy.
Key figures
Experimentally demonstrated the mechanical equivalent of heat in the 1840s, showing that mechanical energy could be converted to thermal energy.
Proved in 1915 that conservation laws (including energy and momentum) are connected to symmetries in the laws of physics.
Established the equivalence of mass and energy with his famous equation E=mc² in 1905.
Part of the Physics Playground
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