First law of thermodynamics facts for kids
The first law of thermodynamics is a very important rule in physics. It says that energy can never be created or destroyed; it can only change from one form to another. This idea is also known as the conservation of energy.
Think of it like this: when you exercise, the energy from the food you ate changes into the energy of movement (called kinetic energy). Or, in the Sun, tiny particles combine (this is called nuclear fusion). This changes a small amount of mass into heat and light. This light travels to Earth and helps plants make food through photosynthesis. When animals eat the plants, that chemical energy helps them move. Energy just keeps changing forms; it never disappears or appears out of nowhere. This is why Perpetual motion machines, which would run forever without any new energy, can't exist. They would break this basic law of physics!
People use these energy changes to do useful things. For example, a car engine changes the chemical energy in fuel into kinetic energy to make the car move. Some common forms of energy you might know are heat, light, kinetic (movement) energy, and potential energy (stored energy).
This law means that the total amount of energy in the whole universe (or in any closed system, which is like a sealed box where nothing can get in or out) always stays the same. Energy can move from one place to another, but the total amount never changes.
Contents
How We Discovered This Law
Early Experiments with Heat and Work
A scientist named James Prescott Joule was one of the first people to show through experiments that heat and work can be changed into each other. He did many tests to prove this.
Clausius's Important Statement
The first clear statement of the first law of thermodynamics was made by Rudolf Clausius in 1850. He said that there's a special property called 'energy'. When a system changes without heat being added or taken away (this is called an adiabatic process), the change in this 'energy' is equal to the work exchanged with its surroundings.
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