Newton s Law of Gravity. Isaac Newton ( ) Newton s Law of Gravity. Newton s Laws of Motion. Newton s Laws of Motion 2/17/17

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1 Isaac Newton ( ) English physicist and mathematician Studied motion, light, and gravity Newton puts all the pieces together Key idea: Mass Mass is the amount of matter in an object NOT the same as weight (to a scientist) You can be weightless, but never massless Everything with mass pulls on everything else with mass Gravity is always attractive The closer the object, the stronger the pull 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) The more massive the body, the more force you need to change its motion Need a lot of force to move a bowling ball If I kick the ball this way If I kick the ball harder, It will move in the same direction It will go faster Only need a little force to move a pingpong ball 1

2 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? The force that I feel due to gravity from will be the force the feels due to gravity from me. A. Greater than B. Less than C. The same as F 1 F 2 The Moon and pull on each other with equal strength and in opposite directions You and pull on each other with equal strength and in opposite directions Moon Wait, I thought I understood this stuff! Shouldn t feel less gravity from me? I ve got a lot less mass than! The more massive the body, the more force you need to change its motion a (acceleration) = F (force) m (mass) Which one will move more: You or? 2

3 F = GMm/r 2 F = GMm/r 2 M = mass of 1st object m = mass of 2nd object r = distance between objects G = gravitational constant = m 3 /s 2 kg r M m Force grows or shrinks with distance squared If you get 2x closer, force is 4x stronger If you get 3x farther away, force is 9x weaker Called Inverse-square relation Net or Total Force Forces are vectors: have strength and direction. We have to consider direction when combining forces: Same direction?! Add Opposite direction?! Subtract Careful: Can only combine forces acting on ONE object at a time! 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. 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 White light is made up of many different colors 3

4 How do light and matter interact? Reflection and Scattering Emission Absorption Transmission Transparent objects let light through Opaque objects block or absorb light Reflection or Scattering Mirror reflects light in a particular direction Movie screen scatters light in all directions What is light? Properties of Waves Light can act either like a wave or like a particle Particles of light are called photons Wavelength is the distance between two wave peaks Frequency is the number of times per second that a wave vibrates up and down 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 4

5 What is the electromagnetic spectrum? What is the electromagnetic spectrum? The entire possible range of wavelengths or frequencies light can have 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 Visible Light Light our eyes can see! Wavelengths about as long as bacteria About nanometers Produced in stars 5

6 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 Electromagnetic (EM) Spectrum of Light L-T: Pg 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. Light & Matter 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 What is the structure of matter? Electron Cloud Atomic Terminology Atomic Number = # of protons in nucleus Atomic Mass Number = # of protons + neutrons Atom Nucleus Molecules: consist of two or more atoms (H 2 O, CO 2 ) 6

7 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 7