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Light a wave
Wavelength () is the distance between successive peaks of a wave Frequency () is the number of wave peaks that pass by an observer per second = the speed of a wave ( = c, for light)
Light is also a particle!
Light particles are called photons The energy of a photon increases as the wavelength of the light decreases A 100-watt light bulb Ephoton = h f emits 31020 photons per
second!
Which travels fastest? a)Gamma rays b)Ultraviolet c)Visible light d)Radio waves e)They all travel at the same speed
Blue light is (compared to red light) a) b) c) d) e) Faster speed Longer wavelength Higher energy photons Only A and C All of the above
Which of the following would be true about comparing gamma rays and radio waves?
a)The radio waves would have a lower energy and would travel slower than gamma rays. b)The gamma rays would have a shorter wavelength and a lower energy than radio waves. c)The radio waves would have a longer wavelength and travel the save speed as gamma rays. d)The gamma rays would have a higher energy and would travel faster than radio waves. e)The radio waves would have a shorter wavelength and higher energy than gamma rays.
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What is the structure of matter?
Ancient Greek philosopher Democritus thought all material were composed of four basic elements: fire, water, earth and air Atoms indivisible not true! More than 100 chemical elements
Atomic Structure
Protons atomic number Neutrons electrons atomic mass number
Atoms are mostly empty space An atom consists of a small, dense nucleus (containing protons and neutrons) surrounded by electrons - Model Proposed by Niels Bohr 1913 A nucleus is about 10-15 m in size and the first electron orbits out at 10-10 m from the center of the atom The size of
the electron orbit is 100,000 times greater than the size of the nucleus
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So if a nucleus the size of an orange (10 cm) was located at the center of the football field, where would the electron be? End Zone?
Grandstands? On Campus? In Bowling Green?
If the electrons orbit is 100,000 times bigger than the nucleus then the electron would be 10,000 m or 6.21 miles away from the center of the Football Field!
TCCW Greenwood mall is about 3.6 miles
The electron should be thought of as a distribution or cloud of probability around the nucleus that on average behave like a point particle on a fixed circular path
Types of Spectra
Continuous spectrum Absorption line spectrum Emission line spectrum
A Spectral Curve
We represent the composition of light with a spectral curve Wavelength (or color) of the light on the horizontal axis Intensity (or energy output per second) on the vertical axis
Continuous Spectrum
Which color of light is most intense in the figure above?
The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption
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Absorption Line Spectrum
Emission Line Spectrum
A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum
A low-density cloud of gas emits light only at specific wavelengths, producing a spectrum with bright emission lines
In-class Activities: Types of Spctra
Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! 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 dont understand what the question is asking, ask me.
The Suns spectrum
Exam #2 on Thursday
Sections 2.3 5.2 Bring pencils and a calculator
Where is the Moon in the orbit?
Sunlight
Sunlight
Sunlight
Third
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E W
Sunset
W E
When does the Moon rise?
Light the from Sun
E W
W E
Sunrise
The position of each phase tells us when its highest in the sky The moon will rise about 6 hours before its highest in the sky and set about 6 hours later
Midnight
Noon
Example: The waning crescent moon is high in the sky around 9:00 AM local time
Eclipses
We see apparent retrograde motion when we pass by a planet
Solar Eclipses
Lunar Eclipses
Although Mars moves steadily along its orbit, it appears (from Earths perspective) to slow to a stop and move westward (retrograde) relative to the background stars as Earth passes it
Keplers First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
Keplers Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times.
The heavens do not move in perfect circles!
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Keplers Third Law
The size of the orbit determines the orbital period more distant planets orbit the Sun at slower average speeds, obeying the relationship
p2 = a3
p = orbital period in years a = avg. distance from Sun in AU
From Keplers third law, an asteroid with an orbital period of 8 years lies at an average distance from the Sun equal to (p2=a3)?
a) b) c) d) e) 2 AU. 4 AU. 8 AU. 16 AU. It depends on the asteroids mass.
Newtons First Law
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 hokey puck glides across the ice at constant speed until it hits something
What are Newtons three laws of motion?
Newtons 2nd law of motion: The acceleration of an object is proportional to the force acting on it and inversely proportional to its mass. F = ma
What are Newtons three laws of motion?
Newtons 3rd law of motion: For every force, there is always an equal and opposite reaction force
A baseball accelerates as the pitcher applies force by moving his arm
A rocket is propelled upward by a force equal and opposite to the force with which gas is expelled out the back
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Conservation of Momentum
Newtons first law The total momentum of interacting objects cannot change unless an external force is acting on them Interacting objects exchange momentum through equal and opposite forces
Conservation of Angular Momentum
Angular momentum = m v r Orbital Keplers 2nd law
Conservation of Energy
Energy can be neither created nor destroyed. It can change form or be exchanged between objects. The total energy content of the Universe was determined in the Big Bang and remains the same today.
The Universal Law of Gravitation
Note that position B is at the midpoint between the Moon and Earth. At which location would the net force be least?
Moon
A
Earth
B
C
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Note that position B is at the midpoint between the Moon and Earth. If a spaceship is traveling from Earth to the Moon, At which position would the acceleration of the ship be greatest? At which position would the acceleration of the ship be least?
Moon
How is mass different from weight?
Mass the amount of matter in an object Weight the force that acts upon an object
A
Earth
B
C
You are weightless in free-fall!
Newtons Law and Gravitation
Projectile motion
Center of Mass
Objects orbiting each other actually revolve around their mutual center of mass Objects of equal mass orbit a point halfway between them Objects of unequal mass orbit a point closer to larger object
Velocity
Acceleration
Force
Escape Velocity
If you want to leave Earth never to return, you must give your spaceship a high enough velocity so it will follow an open orbit This velocity is called At Earths surface, the the escape velocity escape velocity is 11 km/s
(40,000 km/hr)
Tides and Phases
Size of tides depends on phase of Moon
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