main concepts for midterm 1 (review)

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Astronomy & Astrophysics
Stefan Mochnacki

* The definition of Universe: totality of all space, time, energy, matter; has no outside * The age and size of the Universe: 13.7 billion years old - we look back in time when observing things far away, we see how things were when the light left it * The observable Universe: the contents and the limit to which we can see in the universe, cant see past the observable universe * Light travel time and the light year - light year: distance light travels in a year - light year: almost ten trillion km - galaxy hundred billion light years away: light from there takes 100 billion light years to reach us * The contents of the Universe: planets, asteroids, comets, moons, stars, galaxies, solar system * Our location in the Universe: in solar system, milky way galaxy * Gravity and motion - speed: rate at which object moves - Velocity: speed and direction - acceleration: changes in velocity (either speed or direction), same for all objects, mass of object does not matter Driving in a straight line is constant velocity, and no acceleration Objects dropped on the moon fall at the same time, acceleration of gravity same for all objects on moon * Forces and Newtons Laws First law: objects move at constant velocity if no net force acts on it to change directionspeed (spacecraft, planets) Second law: force = mass x acceleration Third law: for every force there is an equal and opposite reaction force (rocket shooting up, earthperson) * Mass vs. weight Mass: amountquantity of matter in an object Weight: the force acting on object and mass * Free-fall: astronauts weightless in space because they are in constant freefall, we experience free fall all the time as well (jumping off chair), planets, moons in free fall Gravity does not allow for any acceleration = free fall, objects in orbit are in constant state of free fall * Momentum: only net force can change momentum , causes acceleration Mass x velocity Angular momentum: rotational momentum of objects that spin or rotate (planet, particle moving in circle). Particles rot. Momentum = mass x velocity x radius Conservation of momentum: momentum between two objects cannot change without net force acting on them, exchange momentum, not lose Reason why objects move at constant velocity without force (Car, elevator) Angular momentum also cannot change without external force (torque), stays constant Why earth continue to orbit sun in same patternmotion, will only change with torque (like tides) Angular momentum is why objects rotate faster with a decrease in radius Force is the rate of change in momentum
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