Lesson 3: Laws of Motion
Lesson 3: Laws of Motion ASTR 101
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This 3 page Class Notes was uploaded by Evan Kirkpatrick on Sunday October 11, 2015. The Class Notes belongs to ASTR 101 at University of Washington taught by Ana Larson in Fall 2015. Since its upload, it has received 12 views. For similar materials see ASTRONOMY (NW,QSR) in Environmental Science at University of Washington.
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Date Created: 10/11/15
Lesson 3 Laws of Motion Vocab Geocentric Model Earth is the center of the solar system Heliocentric Model Sun is the center of the solar system Apparent Retrograde Motion Planets would seem to turn around and move backward Frame of Reference A system where the observer can measure the positions and speeds of two objects using distance and time Empirical Laws Use prior data to predict future behaviors but don t explain why Geometric De nitions 0 Ellipse An oval with symmetry from top to bottom and right to left 0 Semimajor Axis A The average distance between the planet and the Sun 0 Eccentricity e Gives the shape of the ellipse and is determined by the distance between the two foci o Foci Two major points along the major axis Physics De nitions 0 Force A push or pull on an object o Inertia The tendency of an object to remain in it s same state in motion or rest 0 Velocity The combined speed and direction of an object s motion 0 Acceleration The rate at which the velocity is changing Orbit The path an object takes that freely rotates around another Uniform Circular Motion Moving along a circular path at a constant speed Centripetal Force A force toward the center of a circle Circular Velocity The speed at which the satellite is moving around an object Eary Astronomy People believed in a geocentric model Retrograde motion created a problem for the geocentric model Ptolemy attempted to explain the retrograde motion with a complex model of interconnected circles The Copernican Revolution Nicolaus Copernicus famous for placing the Sun at the center of the solar system 0 First to make a mathematical model that explained the solar system 0 Found an estimated distance from the Earth to the Sun Used this information to gure out about how long it took each planet to orbit around the Sun Explained retrograde motion in a simpler model o Planets seem to go backwards because they are moving slower than the Earth Kepler s Laws 1 Planets orbit in an ellipse with the Sun at one focus 2 The area swept out by a planet during a speci c time interval is always the same regardless of where the planet is during its orbit 3 Planets closer to the Sun travel faster than those further from the Sun Galileo First person to use a telescope Determined thatjupiter had 4 moons 0 First observation of something not orbiting the Earth Observed Venus going through phases similar to the Moon These two observations pointed towards the heliocentric model Figured out the gravity accelerates all objects at the same rate on Ea h Newton s 3 Laws of Motion 1 Objects at Rest Stay at Rest While Objects in Motion Stay in Motion 0 Forces can push and pull and balance each other out Forces that cancel out have no effect on the objects motion 0 An object will continue to move in the same direction until a force acts on it to slow it or speed it 0 Similarly an object will remain at rest unless a force acts on it to move it 2 Force Changes an Objects Motion 0 Forces can change either the speed or the direction 0 The speed and direction for the velocity 0 Acceleration is the rate at which the velocity changes Acceleration can be positive or negative 0 Net forces cause acceleration o Inertia also affects acceleration The greater the mass the greater inertia and therefore the greater the force needs to be in order to accelerate the object 3 Whatever is Pushed Pushes Back 0 Every time one object exerts a force on another a matching force is exerted by the second object onto the rst object Exactly as strong but in the opposite direction 0 All forces come in pairs and every pair has an equal strength but opposite direction Gravity Gravity is a force between any two massive objects Newton realized that if all objects accelerate then gravitational force is determined by the object s mass Force of gravity weight mass of the object x Earth s gravitational acceleration Orbits Even though a dropped object falls towards the Earth the Earth also moves towards the object o Earth s mass and inertia make this movement extremely small The Sun exerts a squared amount of force based on the radius of the planet from the Sun 0 Eg lfjupiter is 3 times as far away from the Sun as the Earth is the the Sun s gravitational pull will be 19 the strength that it is on Earth 0 Called the inverse square law Gravitational force between two objects G x Massl x Mass 2 divided by the distance between the two massesquot2 Universal Gravitational Constant G is 6673 x 10quot11 mquot3 Universal Law of Gravitation Gravity is a force between any two objects with mass that have these properties o It is an attractive force between the two objects o It is proportional to the product of the masses of the two objects o It is inversely proportional to the square of the distances between the two objects Newton explained Kepler s Laws using his law of gravitation When a smaller object is orbiting a more massive one the smaller object is called a satellite Bound Orbit The satellite is gravitationally bound to the object it s orbiting Escape Velocity The lowest speed needed to break out of an orbit Unbound Orbit When the satellite no longer orbits around a larger object
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