AST ch 4.odt

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Astronomy & Astrophysics
Michael Reid

4.1 Describing Motion: Examples from Daily Life Speed: How far something will go in a given amount of time Velocity: Speed and direction Accelerations: Occurs when the velocity changes in any way whether in speed, direction or both (speeding up, slowing down or turning) slowing down: When acceleration is in a direction opposite to the motion = negative – this causes the velocity to decrease – turning changes the velocity because it changes the direction in which you are moving therefore turning is a form of acceleration – One of the most important types of acceleration is that caused by gravity – Gravity accelerates all objects by the same amount ex:Abook and pencil will hit the ground at the same time Acceleration of Gravity: The acceleration of a falling object = g. – Gravity makes things fall faster by 10 meters per second (more precisely 9.8) ex: You drop a rock from a tall building it starts at 0m/s after 1 second it will be about 10 m/s after 2 seconds it will be at about 20 m/s. Therefore the acceleration of gravity is about 10 meters per second per second or 10 meters per second squared. 10 m/s² Momentum: The product of an object's mall and velocity (momentum= mass + velocity) Force: The only way to change an object's momentum is to apply a force. Ex:Abug and truck travelling at the same velocity will cause different amounts of damage to your car because the truck has more momentum. The trucks weight is the main factor and it will transfer its momentum like a force onto your care – Changing an object's momentum means changing its velocity as long as the mass is constant – Planets are always accelerating because their orbits are changing the force causing this change is gravity Angular momentum:Any object that is either spinning or moving along a curved path has angular momentum Torque: The type of force that can change an object's angular momentum “twisting force” Mass vs. Weight mass= amount of matter in your body weight= depends both on mass and on the forces acting on your mass including gravity Excellent weightless analogy on page 124 * 4.2 Newton's Laws of Motion Isaac Newton – first discovered that gravity applies to the universe that lies outside of earth Newton's Laws of Motion: Govern the motion of everything from our daily movements to planets #1:An object moves at a constant velocity if there is no net force acting upon it – Objects at rest tend to stay at rest, while objects in motion tend to stay in motion #2: Force = mass x acceleration – You can throw a baseball farther than a shot put (less mass/ greater acceleration) #3: For any force there is always an equal and opposite reaction force – Arocked is propelled upward by a force equal and opposite to the force that propels it forward 4.3 Conservation Laws inAstronomy Laws of Conservation in Astronomy #1 conservation of momentum: the total momentum of interacting objects cannot change as long as no external force is acting on them #2 conservation of angul
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