4.3 conservation laws in astronomy:
DESCRIPTION
4.3 Conservation Laws in Astronomy:. Momentum. Momentum : a property of moving objects Momentum = mass velocity Formula, P = m v A net force changes the momentum of an object. Conservation of Momentum. The total momentum of a system can’t change unless an external force is applied - PowerPoint PPT PresentationTRANSCRIPT
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4.3 Conservation Laws
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Kinetic Energy
• Kinetic energy is the energy associated with motion.
• KE = ½ mv2
• m = mass, v = velocity
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Potential Energy
Potential Energy is stored energy:Gravitational PE depends on:– object’s mass (m)– Acceleration due to
gravity (g)– distance object could
fall– PE = mgh
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PE
• In space, an object or gas cloud has more PE when it is spread out than when it contracts.
A contracting cloud converts gravitational potential energy to thermal energy.
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Radiative Energy – energy from light
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Energy can change forms
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KE & GPE for an orbiting body:
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• Thermal energy is a kind of kinetic energy• Related to temperature but it is NOT the
same
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Thermal energy depends both on temperature AND density. For example:
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• Mass is a form of potential energy•A small amount of mass can release a great deal of energy• E = mc2
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Conservation of Energy
• Energy can’t be created or destroyed.
• It can change form or be exchanged between objects.
• The total energy content of the Universe was determined in the Big Bang and remains the same today.
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Momentum
• Momentum: a property of moving objects
• Momentum = mass velocity
• A net force changes the momentum of an object
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Conservation of Momentum
• The total momentum of a system can’t change unless an external force is applied
• Interacting objects exchange momentum through equal and opposite forces
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• Spinning or orbiting objects have angular momentum
• Angular momentum = mass x velocity x radiusL = m v r
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m x v x R = m x V x r
Conservation of angular momentum: the angular momentum of an object can’t change unless an external twisting force is applied
This explains why objectsrotate faster as they shrink in radius:
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For an orbiting body, this means if r is small, v is big and if r is big, v is small