Transcript Day-15
Astronomy 1010-H Planetary Astronomy Fall_2015 Day-15 Course Announcements • How is the sunset/sunrise observing going? • Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at 7:30pm – at the Observatory. • Exam-2 will be Friday, Oct. 9 • SW-chapter 4 posted: due Mon. Oct. 5 Newton’s First Law of Motion • A body remains at rest or moves in a straight line at a constant speed unless acted upon by an outside (net) force. • A rockets will coast in space along a straight line at constant speed. • A hockey puck glides across the ice at constant speed until it hits something Newton’s Second Law of Motion • (net)Force = mass x acceleration or Fnet = m x a • Acceleration is the rate of change in velocity – or how quickly your motion is changing. • Three accelerators in your car!! Newton’s Third Law of Motion • Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body. • Don’t need a rocket launch pad! • The Bug and the Windshield – who is having the worse day? i-Clicker Question Renaissance Astronomy: Applying Newton's Laws 1 Newton’s Law of Gravitation • Newton’s law of gravitation states: Two bodies attract each other with a force that is directly proportional the product of their masses and is inversely proportional to the square of the distance between them. Gm m 1 2 F grav 2 d What the ….? I thought I understood gravity? Newton’s Law of Gravitation • To figure out the gravitational force just multiply the mass of the two things together then divide by the distance they are apart (squared). Gm m 1 2 F grav 2 d m1 d m2 i-Clicker Question Renaissance Astronomy: Gravity Fundamentals Newton’s Law of Gravitation g ~ 10 m/s2 “the acceleration of gravity” & g x m is your weight! • Newton’s law of gravitation states: Two bodies attract each other with a force that is directly proportional the product of their masses and is inversely proportional to the square of the distance between them. Gm m 1 2 F 2 grav d 2 Nm 11 24 6 . 67 10 5 . 97 10 kg m object 2 kg F grav 6 2 6 .38 10 m F gm grav i-Clicker Question Renaissance Astronomy: Gravity Direction; option 2 MATH TOOLS 4.1 The gravitational acceleration at the surface of Earth, g, can be solved for by using the formula for the gravitational force and Newton’s second law. The m cancels. g is the same for all objects at the same R. CONNECTIONS 4.1 Gravity works on every part of every body. Therefore, self-gravity exists within a planet. This produces internal forces, which hold the planet together. CONNECTIONS 4.1 There’s a special case: spherically symmetric bodies. Force from a spherically symmetric body is the same as from a point mass at the center. Newton’s Laws and Kepler's Laws • Newton’s law of gravitation and his three laws of motion prove all of Kepler’s laws Newton's friend Edmund Halley predicted the comet would return in 1758 and it did! Lecture – Tutorial Newton’s Law of Gravity: pg 29 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don’t understand what the Lecture Tutorial is asking, ask one of us for help.