Transcript 6physics4s
Solar System Physics Astronomy 311 Professor Lee Carkner Lecture 6 Notes Quiz #1 is next Monday (Sept 25) Short answer and multiple choice Covers lectures 1-8 (through “Origin of the Solar System”) Physics and the Solar System There are many physical effects that are important in shaping the solar system We will concentrate on three: Newton’s Law of Universal Gravitation Gravity -- a force that all objects exert on each other proportional to their mass and inversely proportional to the distance squared F=Gm1m2/r2 Inverse square law Using The Gravity Equation If mass is in kilograms and distance is in meters: One newton is the force the Earth exerts on a ¼ pound object on its surface Gravitational Interaction Gravity holds the planets and moons in orbit Gravity can change orbits All orbits have little perturbations caused by the other planets’ gravity Gravity also can cause tidal effects Tides When gravity pulls more strongly on one part of an object than on another the result is a tidal force Example: Tides on the Earth Tries to stretch the Earth into a football shape High and Low Tide Types of Tides High tides and low tides happen twice a day Sun also produces tides Sun’s tidal force about 1/2 that of the Moon Spring Tide -- Neap Tide -- Spring and Neap Tides Synchronous Rotation Why do we always see the same side of the moon? The Earth’s gravity distorts the Moon, slowing its rotation Evaluating a Theory Use the scientific method in detail Use scientific reasoning Rely on others who use the scientific method Should We Believe Scientists? Yes, But, Carkner’s Law: Bottom line, If you can’t evaluate yourself, be skeptical but look for consensus among scientists Magnetic Fields The Sun and many planets produce a magnetic field A magnetic field exerts a force on charged particles Can manifest itself as: Magnetic Field Generation Magnetic fields are generated by the dynamo effect Moving charges produce magnetic fields Generating a magnetic field requires a liquid interior Magnetic fields are dipolar Earth’s Magnetic Field Solar Wind The Sun’s magnetic field heats up its outer layers which produces a stream of fast moving ionized particles Constant stream of ions flowing through solar system Magnetosphere A planets magnetic field interacts with the solar wind to produce a magnetosphere Particles from wind get trapped in magnetic field Size of magnetosphere changes as solar wind ebbs and flows The Earth’s Magnetosphere Charged Particle Belts All planets with magnetic field have particle belts The interaction of the particles and the magnetic fields produce currents The moving particles collide with molecules in the atmosphere exciting them and producing light Summary Physics Gravity, impacts and magnetic fields are responsible for a wide range of solar system phenomena Gravity All solar system bodies effect each other gravitationally, but the effect is often small Strong gravitational fields produce tides Differential gravity creates bulges on opposite sides of a planet Summary Magnetic fields liquid interior allows moving charges to generate field via dynamo magnetosphere deflects solar wind (deflection) magnetosphere traps charged particles (pressure) magnetosphere creates currents (induction)