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Jupiter rules the sky in this labeled view of a starry September night from the Alborz mountains in Iran, complete with the trail of a red flashlight illuminating the mountain road. On September 21st (today) Jupiter is at opposition, the point opposite the Sun along its orbit, rising just as the Sun sets. For this opposition, Jupiter will be slightly brighter and closer to planet Earth than in any year since 1963. Answers to Homework #1 are now posted Homework #2 Questions 1 – 16 due by 5:00 pm, Wednesday. Questions 17 – 20 due by 1:00 pm, Thursday. Homework #3 will be posted shortly, due Tuesday. Exam #1 Thursday, Sept. 30 Review session Tuesday, Sept. 28, time and place to be announced The Activities page of the class website now has a number of out-of-class activities posted. A Universe of Matter and Energy What is matter? What is energy? Matter – material such as rocks, water, air; “stuff” composed of atoms Energy – makes or has the potential to make matter move! The history of the universe, including biological organisms, is based upon the interplay between matter and energy. Three Basic Types of Energy • kinetic – energy of motion • potential – stored energy; e.g., chemical, gravitational, electrical, etc. • radiative – energy transported by light (electromagetic radiation) Conservation of Energy Fundamental law of nature Energy can be neither created nor destroyed It can change form or be exchanged between objects. K.E. The total energy content of the Universe was determined in the Big Bang and remains the same today. P.E. R.E. Kinetic Energy (K.E.): energy of motion K.E. = 1/2 mv2 (m is mass, v is velocity) On the microscopic level: temperature is a measure of the AVERAGE kinetic energy of particles within a substance Temperature Scales Temperature vs. Heat ● ● lower T higher T same T Temperature is the average kinetic energy. Heat (thermal energy) is the total kinetic energy. less heat more heat Sound waves are a form of kinetic energy on a microscopic level (organized vibration of molecules) Applying what we’ve learned - pizza vs. soup caution in the kitchen Potential Energy: Energy that is “stored” within an object and that has the potential of being released in a different form Gravitational Potential Energy ● gravitational potential energy is the energy which an object stores due to its ability to fall g ● It depends on: – – – m the object’s mass (m) the strength of gravity (g) the distance which it can fall (d) ● P.E. = mgd d ● gravitational potential energy ● P.E. = mgd g Mass-Energy Potential Energy ● ● mass-energy: energy is stored in matter itself this mass-energy is what would be released if an amount of mass, m, were converted into energy E = mc2 [ c = 3 x 108 m/s is the speed of light] Chemical Potential Energy ● Chemical potential energy: energy stored chemical bounds There are many additional examples of potential energy. e.g., stretched springs, … Energy, while conserved, can be transformed from one type of energy to another Potential Kinetic Potential Kinetic Kinetic Potential Orbits & Energy Uphill Maximum Potential Energy Maximum Kinetic Energy Downhill From the perspective of energy, which planet is more difficult to reach from the Earth? Mars Venus From the perspective of energy, which planet is more difficult to reach from the Earth? Mars It is “uphill” ConceptTest The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size … (yellow) stays the same (red) slowing changes into other forms of energy (green) slowly increases (blue) interstellar clouds do not have gravitational potential energy ConceptTest The gravitational potential energy of an interstellar cloud of gas that is slowly shrinking in size … (yellow) stays the same (red) slowing changes into other forms of energy (green) slowly increases (blue) interstellar clouds do not have gravitational potential energy ConceptTest In the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is … (yellow) likely to be true (red) false (green) difficult to determine if this will happen or not. (blue) this has already happened, but the government is suppressing this discovery. ConceptTest In the not too distant future scientists will develop an engine that produces more energy than it uses. This statement is … (yellow) likely to be true (red) false (green) difficult to determine if this will happen or not. (blue) this has already happened, but the government is suppressing this discovery. Radiative energy: energy carried by electromagnetic radiation (light). Light An “electromagnetic wave” through which energy is transported. Properties of Waves WAVELENGTH (: Distance between adjacent crests FREQUENCY (f): number of crests that pass through a point each second. It is measured in units of hertz (Hz), which are the number of cycles per second. AMPLITUDE: A measure of the strength of the wave. SPEED (s): how fast the wave pattern moves. For any wave: s=f Light as a Wave • The speed of light is a constant: s = c !!! • Therefore, for light: f=c • The higher f is, the smaller is, and vice versa. • In the visible part of the spectrum, our eyes recognize f (or ) as color! Light as a Particle Light can also be treated as photons – packets of energy. The energy carried by each photon depends on its frequency (color) Energy: E = hf = hc/ [“h” is called Planck’s Constant] Shorter wavelength light carries more energy per photon. The Electromagnetic Spectrum lower energy higher energy