Chap 4 through 6 notes

# An object can gainlose momentum only if some other

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cannot change as long as no external force is acting on them; total momentum is conserved. An object can gain/lose momentum only if some other object's momentum changes by the precis

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opposite amount. The law of conservation of angular momentum is why the earth is able to continually rotate around the sun. As long as there is no external torque, the total angular momentum of a set of interacting objects cannot change. Angular momentum = m (earth's mass) X v (its speed/velocity) X r (radius of the orbit) 1. Earth needs no fuel or push of any kind to keep orbiting the Sun; it will keep orbiting as long as nothing comes along to take angular momentum away. 2. Because Earth's angular momentum at any point in its orbit depends on the product of its speed and orbital radius (distance from the Sun), Earth's orbital speed must be faster when it is nearer to the Sun (smaller radius) and slower when it's further (larger radius). As long as Earth isn't transferring any of the angular momentum of its rotation to another object, it keeps rotating at the same rate The law of conservation of energy tells us that energy can't appear out of nowhere or disappear into nothingness. Objects can gain/lose energy only by exchanging energy w/ other objects. Kinetic energy is energy of motion (falling rocks, orbiting planets, ex) Radiative energy is energy carried by light (all light carries energy) Potential energy is stored energy which can be later converted into kinetic or radiative (rock on a ledge, gasoline) Calories tell us how much energy our bodies drawn from food. In science, the standard unit of energy is the joule. 1 cal = 4182 joules Thermal energy (subcategory of kinetic energy) represents the collective kinetic energy of the many individual particles (atoms and molecules) moving randomly within a substance like a rock, air, or the gas in a star. (The thermal energy of a parked car due to the random motion of its atoms is much greater than the kinetic energy of the car at highway speed) While thermal energy measures the total kinetic energy of all randomly moving particles in a substance, temperature measures the average kinetic energy of the particles. Gravitational potential energy depends on an object's mass and how far it can fall as a result of gravity. Objects have more GPE when higher than lower. (Ex: before a star forms, its matter is spread out in a cloud of gas that has a high GPE. When the cloud contracts, the GPE goes down and the “lost” potential energy gets converted into thermal energy, making the center hot) Mass energy: energy contained in mass itself (E=MC^2) E = energy, m = mass, c = the speed of light Universal Law of Gravitation 1. Every mass attracts every other mass through the force called gravity. 2. The strength of the gravitational force attracting any two objects is directly proportional to the product of their masses. Ex: doubling the mass of one object doubles the force of gravity between the two objects.
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• Fall '10
• TrinhThuan

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