Newton s Laws of Motion

Transcription

1 Newton s Laws of Motion #1: A body continues at rest or in uniform motion in a straight line unless acted upon by a force. Why doesn t the soccer ball move on its own? What causes a soccer ball to roll to a stop on the grass? Newton s Laws of Motion #2: The amount of change in a body s motion is proportional to the force acting on it, and along the same direction as the force. F (force) = m (mass) a (acceleration) If I kick the ball this way It will move in the same direction If I kick the ball harder, It will go faster The more massive the body, the more force you need to change its motion Need a lot of force to move a bowling ball Only need a little force to move a pingpong ball Newton s Laws of Motion #3: When one body exerts a force on a second body, the second body exerts an equal and opposite force back on the first body. What s happening at the moment when I kick the soccer ball? Hint: Think about what would happen if you kicked the ball really hard with no shoes on. Gravity Lecture Tutorial: Pages Work with a partner or two Read directions and answer all questions carefully. Take time to understand it now! Come to a consensus answer you all agree on before moving on to the next question. If you get stuck, ask another group for help. If you get really stuck, raise your hand and I will come around. The Moon and Earth pull on each other with equal strength and in opposite directions Earth Moon 1

2 You and Earth pull on each other with equal strength and in opposite directions The more massive the body, the more force you need to change its motion a (acceleration) = F (force) m (mass) Earth Earth Which one will move more: You or Earth? Light and Matter: Reading Messages from the Cosmos How do we experience light? The warmth of sunlight tells us that light is a form of energy We can measure the power, or flow of energy over time, of light in units of watts One watt is about the amount of power used to lift an apple over your head in 1 second Colors of Light How do light and matter interact? Emission Absorption Transmission Transparent objects let light through Opaque objects block or absorb light Reflection or Scattering White light is made up of many different colors 2

3 Reflection and Scattering What is light? Light can act either like a wave or like a particle Particles of light are called photons Mirror reflects light in a particular direction Movie screen scatters light in all directions Properties of Waves Light: Electromagnetic Waves Wavelength is the distance between two wave peaks Frequency is the number of times per second that a wave vibrates up and down A light wave is a vibration of electric and magnetic fields Light interacts with charged particles through these electric and magnetic fields wave speed = wavelength x frequency Wavelength and Frequency Particles of Light Particles of light are called photons Each photon has a wavelength and a frequency The energy of a photon depends on its frequency wavelength x frequency = speed of light = constant 3

4 Wavelength, Frequency, and Energy λ x f = c λ = wavelength, f = frequency c = 3.00 x 10 8 m/s = speed of light What is the electromagnetic spectrum? The entire possible range of wavelengths or frequencies light can have E = h x f = photon energy h = x joule x s = Plank s constant What is the electromagnetic spectrum? Gamma Rays Very high frequency Very high energy Damaging to humans! -The atmosphere takes care of us Can only be studied from space Gamma ray bursts, nuclear reactions X-rays Still pretty high energy Not as bad as gamma rays, too much is still bad Medical uses Can still only be studied from space Gas in galaxy clusters, supernova remnants, or the Sun s corona Ultraviolet (UV) Light Getting closer to visible light! Too much is still a bad thing (wear sun block ) Visible in supernova remnants and coming from very hot stars 4

5 Visible Light Light our eyes can see! Wavelengths about as long as bacteria About nanometers Produced in stars Infrared (IR) Light We glow in IR light! Beyond the range of human sight Night-vision goggles Given off by planets, some gas clouds, and moons Radio Very wide range of wavelengths / frequencies Subcategories: TV, AM & FM radio, RADAR, microwaves The CMB (cosmic microwave background) glows in microwaves EM Spectrum Lecture Tutorial: Pages Work with a partner or two Read directions and answer all questions carefully. Take time to understand it now! Come to a consensus answer you all agree on before moving on to the next question. If you get stuck, ask another group for help. If you get really stuck, raise your hand and I will come around. Telescopes & Light Telescopes gather information from the entire EM spectrum Why do some objects glow in IR light? Why do some give off x-rays? Interactions between light & matter Properties of Matter Structure of matter Phases of matter How energy is stored in atoms How do light and matter interact? 5

6 What is the structure of matter? Electron Cloud Atomic Terminology Atomic Number = # of protons in nucleus Atomic Mass Number = # of protons + neutrons Atom Molecules: consist of two or more atoms (H 2 O, CO 2 ) Atomic Terminology Isotope: same # of protons but different # of neutrons. ( 4 He, 3 He) What are the phases of matter? Familiar phases: Solid (ice) Liquid (water) Gas (water vapor) Phases of same material behave differently because of differences in chemical bonds Phase Changes Melting: Breaking of rigid chemical bonds, changing solid into liquid Evaporation: Breaking of flexible chemical bonds, changing liquid into gas Dissociation: Breaking of molecules into atoms Ionization: Stripping of electrons, changing atoms into plasma How is energy stored in atoms? Excited States Ground State Electrons in atoms are restricted to particular energy levels (electron shells) 6

7 Energy Level Transitions An electron can only go from one level to another, not in between A Simple Atom Only 2 energy levels Ground (E1) Excited (E2) Right now electron is at E1 Not Allowed Allowed E1 E2 A Simple Atom A Simple Atom Excitation Electron absorbs a photon and jumps from E1 to E2 Photon only absorbed if it has energy = (E2-E1) Photon E1 Ionization Electron absorbs a photon and leaves! Only works if electron is in higher energy levels Photon E1 E2 E2 A Simple Atom Spectrum: Wavelength vs. Intensity De-excitation Electron emits a photon of energy (E2-E1) Electrons like to be in the ground state Photon Visible: Intensity vs. wavelength plot: E1 E2 7

8 They show the same information Continuous Spectrum Dips in color = black lines All wavelengths, no breaks Rainbows! Dips in intensity Emission Spectrum Absorption Spectrum Bright, individual lines Also called bright-line spectrum Electrons are moving to lower energy levels, emitting photons of light Rainbow with dark lines on top Also called dark-line spectrum Atoms in the cloud are absorbing photons, moving to higher energy levels Kirchhoff s Laws I. A hot, dense substance will give off continuous spectrum II. A hot, low-density gas will give off an emission spectrum III. A cool, low-density gas in front of a continuous-spectrum source will give off an absorption spectrum Chemical Fingerprints Energy levels of Hydrogen Each type of atom has a unique set of energy levels Each transition corresponds to a unique photon energy, frequency, and wavelength 8

9 Chemical Fingerprints Downward transitions produce emission lines Upward transitions produce absorption lines Chemical Fingerprints Each type of atom has a unique spectral fingerprint, due to spacing of energy levels Light and Atoms Lecture Tutorial: pages Work with a partner or two Read directions and answer all questions carefully. Take time to understand it now! Come to a consensus answer you all agree on before moving on to the next question. If you get stuck, ask another group for help. If you get really stuck, raise your hand and I will come around. 9