chapter 4 astronomy

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University of Toronto St. George
Astronomy & Astrophysics
Stefan Mochnacki

20:44 4.1 describing motion speed: how far it will go in a certain amount of time velocity: describes both its speed and direction acceleration: changes in velocity whether speed or direction acceleration works both speeding up or slowing down one of most important acceleration: gravity galileo: throw weights from leaning tower of pisa learned that gravity accelerates all objects in same amount regardless of mass the difference in acceleration is caused by air resistance acceleration of falling object acceleration of gravity on earth 9.8 meters every second (around 10m) momentum = mass X velocity only way to change an objects momentum is to apply force to it when net force = 0, you can be moving in a circle or curved road angular momentum is turning momentum when earth rotations, rotational angular momentum when earth orbits sun, orbital angular momentum torque -type of force that can change an objects angular momentum torque depends on how much force applied but also where mass amount of matter in your body (same everywhere) weight force that a scale measures when you stand on it (depends on mass and forces (gravity) acting on it) elevator: when stationary or moving at constant velocity, your weight is the same when accelerating upwards, floor exerts more force so your weight measured is heavier when accelerating downwards, floor exerts weaker force so your weight is much lighter if elevator breaks (free fall) with no resistance, you would have zero weight (floor exerts no force on you) weightlessness weightlessness in space not because theres no gravity but they are at free fall all the time orbital altitude of 28,000 kmhr if you jump that fast you would be orbiting around earth instead of falling 4.2 newtons law of motion newton destroyed Aristotles physics and brought earth and the heavens into one universe his insights became the birth of astrophysics newton published laws of motion and gravity which govern everything from daily movements to movements of stars throughout the universe an object moves at constant velocity if there is no net force acting upon it
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