Astronomy 101 The Solar System Tuesday, Thursday Tom Burbine [email protected] #1, 2, 3, 4, and 5Exam #1Slide 5Kepler’s Three LawsOrbitsArguments against the Sun being the center of the solar systemGalileo Galilei (1564-1642)He alsoSlide 11Galileo also found that Venus orbited the SunAccelerationSlide 14Difference between mass and weightIsaac Newton (1642-1727)ForceGravityNewton’s 1st LawWhy do things on Earth not remain in motion?Slide 21Newton’s 2nd LawNewtonHow much do you weigh?Newton’s 3rd LawSlide 26Newton’s Universal Law of GravitationFormulaSlide 29So what should you know about this formulaSlide 31What is the attraction of two people in this room?Slide 33Slide 34Slide 35Acceleration of gravity (g)Slide 37Gravitational accelerationExperiment on the MoonHow things fallHow does gravity work?Escape velocitySlide 43Slide 44What causes tides on earth?Forces on WaterSlide 47Slide 48Slide 49Slide 50Effects on tides due to SunSlide 52RememberSlide 54Shoemaker-Levy 9Roche LimitWhy is the Roche Limit important?Slide 58Impact of Shoemaker-Levy 9Slide 60Slide 61Has this happened before? GanymedeAny Questions?Astronomy 101The Solar SystemTuesday, ThursdayTom [email protected]•Course Website:–http://blogs.umass.edu/astron101-tburbine/•Textbook:–Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny.•You also will need a calculator.HWs #1, 2, 3, 4, and 5•HWs on Spark:•If you can’t get on Spark, the HWs are also on the website:•http://blogs.umass.edu/astron101-tburbine/•Due Date: February 2, 2010 1:00 PMExam #1•Next Thursday•Covers all material from January 19-28•A hypothesis is an educated guess, based on observation. Usually, a hypothesis can be supported or refuted through experimentation or more observation. A hypothesis can be disproven, but not proven to be true. •A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven.•A law generalizes a body of observations. At the time it is made, no exceptions have been found to a law.Kepler’s Three Laws•http://brunelleschi.imss.fi.it/museum/esim.asp?c=500106Orbits•all the planets orbit the Sun in a counterclockwise direction (but they do not orbit it at the same rate). •The Earth rotates counterclockwise•The Sun, the Moon, the planets, and the stars all rise in the east and set in the westArguments against the Sun being the center of the solar system•1) If the Earth was moving, objects such as birds and clouds would be left behind as the Earth moved•2) The heavens must be perfect and unchanging. Noncircular orbits do not fit this model•3) Stellar parallax would be observableGalileo Galilei (1564-1642)•He was able to figure out answers to these arguments•1) Things in motion tend to remain in motion.•2) He used a telescope to see sunspots on the Sun and features on the Moon.•3) Galileo found that stars were more numerous and more distant than imaginedHe also•He discovered the moons of Jupiter and saw that they were orbiting Jupiter–Io–Europa –Ganymede –Callisto•Proving that bodies could orbit other bodies besides the EarthGalileo also found that Venus orbited the SunAcceleration•Acceleration is when your velocity is changing•Velocity not changing, no accelerationAcceleration•a = ∆v/∆t•Car is travelling at 10 m/s•Increases its speed to 30 m/s over 5 seconds•a = (30 m/s – 10 m/s)/5 seconds•a = 4 m/s2Difference between mass and weight•Mass is the amount of matter in your body•Weight is the amount of force acting on your body•So on the Moon, you would have the same mass as on Earth but weigh less on the Moon since the Moon is less massive than Earth•Supposedly saw an apple fall to the ground•He then understood that gravity was universal, meaning it affected both the planets and us on Earth•Came up with 3 Laws of MotionIsaac Newton (1642-1727)Force•Force – anything that can cause a body to change velocityGravity•Gravity is a natural phenomenon by which objects with mass attract one another.Newton’s 1st Law•In the absence of a net (overall) force acting upon it, an object moves with a constant velocity•An object at rest remains at rest•An object in motion tends to remain in motion unless a force is acting upon itWhy do things on Earth not remain in motion?Why do things on Earth not remain in motion?•FrictionNewton’s 2nd Law•Force = mass x acceleration•Units of Force kg m/s2 = newtonNewton•A Newton is equal to the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second per secondHow much do you weigh?•So much do you weigh•Say your mass is 100 kg•F = 100 kg x 9.8 m/s2 •F = 980 Newtons•9.8 m/s2 is the acceleration of gravity on Earth•This is the acceleration due to the Earth’s gravitational fieldNewton’s 3rd Law•For any force, there is an equal and opposite reaction force•Gravity is holding you on the ground•The ground is also pushing back up on you with the same amount of forcehttp://www.vshiksha.com/system/files/u1/pslvc6-rocket.jpgNewton’s Universal Law of Gravitation•Every mass attracts every other mass through the force called gravity•Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. •The force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between the point massesFormula•Newton came up with this formulaForce is proportional to M1 M2 r2M1, M2 are the masses of the two objectsr is the distance between the objects•If you want to calculate actual forcesF = G M1 M2 r2M1, M2 are the masses of the two objectsr is the distance between the objectsG = constant = 6.67 x 10-11 m3/(kgs2)So what should you know about this formulaF = G M1 M2 r2•The force of attraction between any two objects is directly proportional to the product of their masses•The force of attraction between two objects decreases with the square of the distance between their centers•G is a very small numberassume all mass is concentrated in the center of a body r rWhat is the attraction of two people in this room?F = G M1 M2 r2•Say their masses are both 100 kg•Their distances are 10 meters apart•F = 6.67 x 10-11
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