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by: Iman Usmani

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2

# PY 205 Week 5 PY 205

Iman Usmani
NCS

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Notes on gravitational force and Hooke's Law.
COURSE
Physics for Engineers and Scientists
PROF.
Professor Dougherty
TYPE
Class Notes
PAGES
2
WORDS
CONCEPTS
Physics
KARMA
25 ?

## Popular in Engineering and Tech

This 2 page Class Notes was uploaded by Iman Usmani on Wednesday February 10, 2016. The Class Notes belongs to PY 205 at North Carolina State University taught by Professor Dougherty in Winter 2016. Since its upload, it has received 13 views. For similar materials see Physics for Engineers and Scientists in Engineering and Tech at North Carolina State University.

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Date Created: 02/10/16
PY 205 Week 5 Newton’s Law of Universal Gravitation - The force of gravitation exerted on one particle by a second particle is always directed toward the second particle o The total force on one particle is the vector sum of the forces exerted by each of the others - Gravity near the earth’s surface o The force of gravity due to the Earth is the weight of the object  mg = G m(mE) / r^2 where mE is the mass of the Earth o The acceleration of the gravity at Earth’s surface is dependent on mE and rE^2 - Satellites and weightlessness o Satellite motion – if the speed is too high, the satellite will be lost. If the speed is too low, it will return to Earth. o Usually put into a circular orbit because it requires the least takeoff speed o High speeds keep satellites up o Satellites are free falling o G m(mE) / r^2 = mv^2 / r  r is the sum of the earth’s radius plus the height above the Earth  The Earth’s radius is 6380 km o Weightlessness – in an elevator, the downward and upward force exerted are equal to the work since there is no acceleration  W = mg  W – mg = 0  If there is acceleration, then ma + mg = w - Kepler’s Laws o The path of each planet about the sun is an ellipse with the sun at one focus o Each planet moves so that the imaginary line drawn from the sun to the planet sweeps out equal areas in equal areas of time o The ratio of the squares of the periods of any two planets revolving about the sun is equal to the ration of the cubes of their semi-major axis - Gravitational field – surrounds every object that has mass and this field permeates all of space o Gravitational force per unit mass at any point in space - Work and energy o Work – the product of displacement of an object and a component of the force in the direction of the displacement  Fr cosO = work done by F  Scalar quantity so it can be positive or negative - Multiplying two vectors o Definition: the scalar product of the two vectors  A O B = AB cosO (where “AB” is the magnitude of each multiplied) - Hooke’s springs o Hooke’s law: Frestoring = R(x-xO) --- where x-x0 is the linear displacement o The spring constant is k - To calculate the kinetic coefficient – the sum of all the forces = the mass times the acceleration o Find the retarding force – which is the force of friction o Then consider the normal force – ma = mg(uk)

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