the shuttle blasts off Then comes the tremendous pressure of three G s and the sudden release into weightlessness as the ship leaves the gravitational field behind -from The Arizona Republic 1
Chapter 5 Newton, Einstein, and Gravity
Outline I. Galileo and Newton A. Galileo and Motion B. Newton and the Laws of Motion C. Mutual Gravitation II. Orbital Motion and Tides A. Orbits B. Orbital Velocity C. Calculating Escape Velocity D. Kepler's Laws Re-examined E. Newton's Version of Kepler's Third Law F. Tides and Tidal Forces G. Astronomy After Newton III. Einstein and Relativity A. Special Relativity B. The General Theory of Relativity C. Confirmation of the Curvature of Space-Time
Newton s 1st Law of Motion An object continues in a state of rest or in a state of uniform motion at a constant speed along a straight line unless compelled to change that state by a net force. Why? Because objects have inertia 4
Inertia The tendency that Newton observed for objects at rest to stay at rest and objects in motion to stay in uniform motion in a straight line. How do we measure inertia? MASS 5
Force Net force = sum of all forces: Here, we say that the NET force is zero! The box stays at rest. There is no change in its state of motion no net force is acting on it. 6
Acceleration A change in velocity (state of motion) Refers to an increase in velocity OR a decrease in velocity OR a change in the direction of velocity. A net force acting on an object will cause that object to accelerate. 7
Newton s 2nd Law of Motion The amount of acceleration (a) produced by a force(f) depends on the mass (m) of the object being accelerated. Mathematically: Alternatively: F = m a a = F/m 8
Law of Gravitation G=6.67 10-11 9
Weight Weight: Weight is NOT the same as mass. Weight is equivalent to the gravitational force the Earth exerts on your body. 10
Are you weightless on the Moon? a) yes b) no c) depends Is there gravity on the Moon? 11
Weight on other planets Weight on Earth, Mars, and Saturn: M mars = 0.1 M earth R mars = 0.5 R earth M saturn = 95 M earth R saturn = 9.4 R earth 12
Are the astronauts orbiting the Earth weightless? a) yes b) no c) depends 13
Understanding Orbital Motion The universal law of gravity allows us to understand orbital motion of planets and moons: Example: Earth and moon attract each other through gravitation. Since Earth is much more massive than the moon, the moon s effect on Earth is small. Earth s gravitational force constantly accelerates the moon towards Earth. This acceleration is constantly changing the moon s direction of motion, holding it on its almost circular orbit. v v Moon F Earth
Orbital Motion (2) In order to stay on a closed orbit, an object has to be within a certain range of velocities: Too slow => Object falls back down to Earth Too fast => Object escapes Earth s gravity
Geosynchronous Orbits
What s wrong with this. the shuttle blasts off Then comes the tremendous pressure of three G s and the sudden release into weightlessness as the ship leaves the gravitational field behind -from The Arizona Republic 17
Chapter 6 Light and Telescopes
Outline I. Radiation: Information from Space A. Light as a Wave and a Particle B. The Electromagnetic Spectrum II. Optical Telescopes A. Two Kinds of Telescopes B. The Powers of a Telescope C. Buying a Telescope D. New-Generation Telescopes E. Interferometry III. Special Instruments A. Imaging Systems B. The Spectrograph
Outline (continued) IV. Radio Telescopes A. Operation of a Radio Telescope B. Limitations of the Radio Telescope C. Advantages of Radio Telescopes V. Astronomy from Space A. The Ends of the Visual Spectrum B. Telescopes in Space C. Cosmic Rays
Properties of Light Wave-like properties: Reflection, refraction, diffraction, interference Electromagnetic waves Particle-like properties: Energy carried in bundles we call photons Can propagate through a vacuum 21
Wavelength Wavelength: distance between crests 22
Frequency The number of peaks which pass you per second. Units: Hz 23
Speed of wave Speed = distance = wavelength frequency time c = λ f = 3 10 5 km/s 24