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Charles Hakes Fort Lewis College 1 Chapter 1 Newton and Gravity Charles Hakes Fort Lewis College 2 Outline • • • • Notes Kepler Review Newton’s laws Gravity Charles Hakes Fort Lewis College 3 (Lab) notes • Remove folder debris • Do Kepler small group lab this week. • Due Friday at 6:30 P.M. • In box outside room 671. • Sunset 2 - you MUST have Sunset 1 completed and returned FIRST • Due Friday in one week. Charles Hakes Fort Lewis College 4 Review • Did not get thrown into the abyss: 1 • Other favorite answers… • • • • • • The speed of light. I don’t know - I’m not king! My Holy hand grenade blew it up “42”: (mixing your fiction). I’m from Oklahoma and have no clue … for a chimney swallow while hunting mosquitoes…. Charles Hakes Fort Lewis College 5 Review • What was the most important thing you learned? • A circle is actually a special kind of ellipse with only one focal point • A square is to a rectangle as a circle is to an ellipse • The semi-major axis is half of the major axis. • If the semi-major axis of two bodies is the same, they take the same amount of time to orbit. Charles Hakes Fort Lewis College 6 Group Exercise • Assume a comet has a period of 5.2 years, with eccentricity very close to 1. Charles Hakes Fort Lewis College 7 Group Exercise • • Assume a comet has a period of 5.2 years, with eccentricity very close to 1. Calculate the semi-major axis. Charles Hakes Fort Lewis College 8 Group Exercise • • • • • Assume a comet has a period of 5.2 years, with eccentricity very close to 1. Calculate the semi-major axis. p2 = a 3 What is the major axis? What is the maximum distance this comet might ever get from the Sun? Include copy of work in your folder. Charles Hakes Fort Lewis College 9 Figure 1.20 Isaac Newton (1642-1727) Charles Hakes Fort Lewis College 10 An iron weight and a styrofoam ball are dropped from the same height at the same time. Which hits the ground first? A) The iron weight B) The styrofoam ball C) They hit at the same time Charles Hakes Fort Lewis College 11 Newton’s “Laws” Charles Hakes Fort Lewis College 12 Newton’s 1st Law If there are no external forces on an object, then: • If it is at rest, it will stay that way - forever. • If it is moving, it will keep doing so at constant velocity, in a straight line - forever. Charles Hakes Fort Lewis College 13 Newton’s 1st Law • Inertia - the natural tendency of an object to stay at rest, or remain moving with a constant velocity. • Mass is a quantitative measure of inertia. Charles Hakes Fort Lewis College 14 Momentum • Momentum - the product of mass and velocity. momentum = mass x velocity • A concept related to Inertia • Momentum (both linear and angular) must be conserved. Charles Hakes Fort Lewis College 15 Which object has the most momentum? A) A cruise missile B) A ship C) A glacier D) Need more information Charles Hakes Fort Lewis College 16 Which object has the most momentum? A - A cruise missile 1000 kg 100m/s B - A ship 10 million kg = 107 kg 10 m/s C - A glacier 1012 kg 1 m/day (~10-5 m/s) Charles Hakes Fort Lewis College 17 Which object has the most momentum? A - A cruise missile B - A ship C - A glacier Charles Hakes Fort Lewis College 18 Angular momentum demonstration Charles Hakes Fort Lewis College 19 Angular momentum demonstration • This is why planets move faster closer to the sun. Charles Hakes Fort Lewis College 20 Newton’s 2nd Law • The net force on an object is equal to the mass of the object times the acceleration of the object F =ma net • The SI units of force are newtons (N). Charles Hakes Fort Lewis College 21 Newton’s 2nd Law • • • Force - something that is capable of changing an object’s state of motion (it’s velocity) Fnet - the sum of all forces on an object Dynamics - the study of changes in motion and what causes those changes Charles Hakes Fort Lewis College 22 Newton’s 2nd Law Fnet = m a Charles Hakes Fort Lewis College 23 Newton’s 3rd Law • …the one hard to believe… Charles Hakes Fort Lewis College 24 A brick hits a glass window. The brick breaks the glass, so the magnitude of the force of the brick on the glass is A: is greater than the magnitude of the force of the glass on the brick B: is smaller than the magnitude of the force of the glass on the brick C: is equal to the magnitude of the force of the glass on the brick D: none of the preceding Charles Hakes Fort Lewis College 25 Newton’s 3rd Law • For every action (force) there is an equal and opposite reaction (force). • Important note - the action-reaction force pairs do NOT act on the same object. Charles Hakes Fort Lewis College 26 A brick hits a glass window. The brick breaks the glass, so the magnitude of the force of the brick on the glass is A: is greater than the magnitude of the force of the glass on the brick B: is smaller than the magnitude of the force of the glass on the brick C: is equal to the magnitude of the force of the glass on the brick D: none of the preceding Charles Hakes Fort Lewis College 27 Gravity Charles Hakes Fort Lewis College 28 Figure 1.22 Gravity Charles Hakes Fort Lewis College 29 Figure 1.24 Sun’s Gravity Charles Hakes Fort Lewis College 30 Gravity • • Any object having Mass will exert a gravitational force on other massive objects. Force is proportional to mass of each object F M1 M2 Charles Hakes Fort Lewis College 31 Gravity • • • Any object having Mass will exert a gravitational force on other massive objects. Force is proportional to mass of each object Force decreases with the square of the distance between the two objects F M1 M2 / r2 Charles Hakes Fort Lewis College 32 Figure 1.23 Gravitational Force • Any object having Mass will exert a gravitational force on other massive objects. F M1 M2 / r2 Charles Hakes Fort Lewis College 33 Gravity • • • • • Any object having Mass will exert a gravitational force on other massive objects. Force is proportional to mass of each object Force decreases with the square of the distance between the two objects Proportionality constant is “G”, the universal gravitational constant G = 6.67x10-11 (N m2/kg2) F = G M1 M2 / r2 Charles Hakes Fort Lewis College 34 Gravity F = G M1 M 2 / r 2 Charles Hakes Fort Lewis College 35 Newton • Modification to Kepler’s 1st Law • Both the Sun and the planet orbit about the center of mass of the system. Charles Hakes Fort Lewis College 36 Figure 1.25 Orbits Charles Hakes Fort Lewis College 37 Newton • Modification to Kepler’s 3rd Law • That “math” law - updated P2 (years) = a3 (astronomical units) Mtotal(solar units) • For planets around the Sun, this makes very little difference except for (even for) Jupiter (0.1% Msun) Charles Hakes Fort Lewis College 38 Which mass pair has the greatest gravitational force between them? 1: A 5Msolar mass and a 4Msolar mass separated by 4 AU. 2: A 4Msolar mass and a 3Msolar mass separated by 3 AU. 3: A 3Msolar mass and a 2Msolar mass separated by 2 AU. 4: A 2Msolar mass and a 1Msolar mass separated by 1 AU. Charles Hakes Fort Lewis College 39 Which mass pair has the greatest gravitational force between them? 1: A 5Msolar mass and a 4Msolar mass separated by 4 AU. 2: A 4Msolar mass and a 3Msolar mass separated by 3 AU. 3: A 3Msolar mass and a 2Msolar mass separated by 2 AU. 4: A 2Msolar mass and a 1Msolar mass separated by 1 AU. Charles Hakes Fort Lewis College 40 Group Exercise Calculate the force between those two masses. A 2Msolar mass and a 1Msolar mass separated by 1 AU. Charles Hakes Fort Lewis College 41 Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 42