Internal energy physics OCR Unit 4 - thermal physics

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brainmatter
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in terms of the physics of internal energy, why is it that ice is less dense than water? and how do internal energy and density relate?
also why does the speed of the whole body have no contribution to the internal energy?
surely if the body is moving faster then a rise in temperature has occurred and therefore there is a gain in internal energy?
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Actaeon
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With regard to the second half, temperature is really a measure of internal energy, that is, the energy of all the particles within the substance. This is a microscopic energy, and doesn't depend on macroscopic factors, like the entire body moving. Think about a moving object: at rest, the particles of the object vibrate with a certain energy. If you apply an external force to the body, it will move relative to its surroundings, but the energy of the constituent particles remains pretty much the same. A change in kinetic and potential energy of the entire body doesn't translate to a change in the energy of its particles
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brainmatter
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(Original post by Actaeon)
With regard to the second half, temperature is really a measure of internal energy, that is, the energy of all the particles within the substance. This is a microscopic energy, and doesn't depend on macroscopic factors, like the entire body moving. Think about a moving object: at rest, the particles of the object vibrate with a certain energy. If you apply an external force to the body, it will move relative to its surroundings, but the energy of the constituent particles remains pretty much the same. A change in kinetic and potential energy of the entire body doesn't translate to a change in the energy of its particles
Thank you! thats really helpful, but i still dont understand why the kinetic energy and potential energy have no effect on the microscopic molecules if it is said that when the temperature increases then the kinetic energy of the molecules increases; also the potential energy of particles in gases is greater than that of solids, so how does this mean that the energy of the constituent particles remain the same if there are changes in the surrounding such as state and temperature? :confused:
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Aruna Pandya
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a sample of alcohol is heated with a 4oW heater until it boils.as it boils, the mass of the liquid decreases at a rate of 2.25g per minute. assuming that 80% of the energy supplied by the heater is transferred to the alcohol, estimate the specific latent heat of vaporisation of the alcohol.
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