Total energy is conserved because, in an isolated system, the total amount of energy remains constant over time; energy can transform from one form to another or be transferred between objects, but it cannot be created or destroyed.
Here's a breakdown:
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The Law of Conservation of Energy: This fundamental law of physics states that the total energy of an isolated system remains constant.
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Isolated System: An isolated system is one where no energy or matter can enter or leave. In reality, perfectly isolated systems are difficult to achieve, but many systems can be approximated as such for specific timeframes.
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Energy Transformation: Energy can change forms. For example:
- Potential Energy (energy due to position or condition) can be converted to Kinetic Energy (energy of motion) when a ball rolls down a hill.
- Chemical Energy (energy stored in chemical bonds) is converted to Thermal Energy (heat) and Light Energy during combustion (burning).
- Electrical Energy can be converted to Light Energy in a light bulb.
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Energy Transfer: Energy can also be transferred between objects or locations within a system. For example, heat transfer occurs between objects of different temperatures until they reach thermal equilibrium.
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Closed System: A closed system is similar to an isolated system but allows energy to be transferred in or out (but not matter). In a closed system, the total energy within the system changes only by the amount of energy added to or removed from the system.
Examples:
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A bouncing ball: Initially, the ball has potential energy at its highest point. As it falls, potential energy is converted to kinetic energy. When it hits the ground, some kinetic energy is converted into sound and heat, but most is converted back into potential energy, causing it to bounce back up (though not as high due to some energy loss). The total energy of the ball and its surrounding environment (air, ground) remains constant.
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A hydroelectric dam: The potential energy of water held behind the dam is converted to kinetic energy as it flows through turbines. The turbines then convert kinetic energy into electrical energy. Although energy changes form, no energy is created or destroyed.
Implications:
The conservation of energy is a cornerstone of physics with broad implications:
- It helps us understand and predict the behavior of physical systems.
- It is crucial for designing efficient machines and processes.
- It explains why perpetual motion machines (machines that run forever without an external energy source) are impossible.
