Bernoulli s Principle. Application: Lift. Bernoulli s Principle. Main Points 3/13/15. Demo: Blowing on a sheet of paper

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1 Bernoulli s Principle Demo: Blowing on a sheet of paper Where the speed of a fluid increases, internal pressure in the fluid decreases. Due to continuous flow of a fluid: what goes in must come out! Fluid flows faster through a narrower pipe Bernoulli s Principle If speed of a fluid increases, the pressure in the fluid decreases. This phenomenon is due to energy conservation; when fluid s KE increases (velocity increases) its internal P (pressure) decreases. Application: Lift Airplane wings at an angle produce more crowded streamlines along the top of the wing than along the bottom Avg. pressure difference x surface area of wing = net upward force This works even when the plane flies upside down, as long as the angle is similar! Water is flowing continuously in the pipe from point A to point C. Rank the three points in terms of the internal pressure from biggest to smallest. Chapter 12: Density Chapter 13: Pressure Pressure in liquids Buoyancy Archimedes Principle Pascal s Principle Main Points Chapter 14: Pressure in gases Boyle s Law Buoyancy in air Bernoulli s Principle 1

2 Part 3: Heat Chapter 15: Temperature, Heat, & Expansion Chapter 16: Heat Transfer Chapter 17: Change of Phase Chapter 18: Thermodynamics Temperature Temperature (T) is a measure of how hot or cold something is Temperature measures the random KE of each particle in an object. The greater the motion/vibration the greater the T The smaller the motion/vibration the lower the T SI Unit: kelvin (K) Room temperature is about 295K Other Temperature Scales Celsius Water freezes at 0ºC, boils at 100ºC Fahrenheit Water freezes at 32ºF, boils at 212ºF Kelvin Temp. Scale The Kelvin scale has the same step size (size of one degree) as the Celsius scale, but the Kelvin scale has its zero at absolute zero. Conversion between a Celsius temperature and a Kelvin temperature: Heat (Q) Definition of heat: Heat is the energy transferred between objects because of a temperature difference. Objects are in thermal contact if heat can flow between them. 2

3 Thermal Equilibrium When the transfer of heat between objects in thermal contact stops, they are in thermal equilibrium. The objects will then be at the same temperature. Units of Heat Since heat is just a flow of energy, the SI unit is the energy unit, the joule (J). Other heat units calorie (cal): Heat needed to raise temperature of 1 gram of water by 1 C (or 1 K) Calorie (Cal or kcal): Heat needed to raise temperature of 1 kg of water by 1 C (or 1 K) Calorie also used to measure energy content of food Conversions: 1 cal = J 1 kcal = 1 Cal (food Cal.) = kj Thermometers Thermometers are instruments designed to measure temperature. In order to do this, they take advantage of some property of matter that changes with temperature. Length of a solid or liquid column Volume of a solid, liquid, or gas Electromagnetic waves (infrared light) given off by hot objects Specific Heat Capacity Specific heat capacity is the amount of heat energy required to raise the temperature of one unit mass of a material by one degree. SI Unit: J/(kg K),or J/(kg C) Thermometers Thermometers are instruments designed to measure temperature. In order to do this, they take advantage of some property of matter that changes with temperature. Length of a solid or liquid column Volume of a solid, liquid, or gas Electromagnetic waves (infrared light) given off by hot objects Thermal Expansion When you heat something up, it expands! The effect is less dramatic in solids than in liquids or gases Demos: bimetallic strip, and metal ball & ring 3

4 Common Thermometers Liquid-in-tube Bimetallic Strip Chapter 16: Heat Transfer Conduction: Thermal kinetic energy passed from particle-to-particle along a length of material. Convection: Thermal energy carried by moving fluid. Radiation: Thermal energy carried by electromagnetic waves (light) Conduction Heat conduction can be visualized as occurring through molecular collisions. Thermal kinetic energy is passed along as hotter particles collide with colder ones. Conduction is heat flow by direct contact. Some materials are good thermal conductors (like the tile), others are insulators (like the wood). Conduction Convection Convection is flow of fluid due to difference in temperatures, such as warm air rising. Fluid carries heat with it as it moves. Natural convection: Warm fluid will rise because it is less dense then cold fluid. Convection Heat transfer in a fluid often occurs mostly by convection. Buoyancy causes warm air to rise, which carries thermal energy directly by its motion. 4

5 Convection oven has a fan to enhance the circulation of the air, increasing the transfer of heat. Convection Oven Fiberglass Insulation Air is a poor thermal conductor but easily transfers heat by convection. Fiberglass insulation is mostly air, with the fibers disrupting the convection flow. Radiation How does energy get from the Sun to Earth? No atmosphere out in space, so it s can t be convection or conduction The energy is transferred through radiation; specifically, electromagnetic radiation Radiation Radiation has many different wavelengths, most of which are not visible to the eye. All radiation carries energy, and thus transfers heat. The Electromagnetic Spectrum Gamma Rays X-rays Ultraviolet Light Visible Light (ROY G BIV) Infrared Light Microwaves & Radio Waves Properties of Waves 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 5

6 Wavelength and Frequency Frequency vs. Temperature wavelength x frequency = speed of light = constant The Electromagnetic Spectrum Gamma Rays X-rays Ultraviolet Light Visible Light (ROY G BIV) Infrared Light Microwaves & Radio Waves How do light and matter interact? Emission Absorption Transmission Transparent objects let light through Opaque objects block or absorb light Reflection or Scattering Reflection and Scattering The Greenhouse Effect Glass is transparent to sunlight (short-wavelength). Glass is opaque to infrared radiation (longwavelength) produced by objects inside greenhouse, trapping the heat. Mirror reflects light in a particular direction Movie screen scatters light in all directions 6

7 Earth s Greenhouse Effect Earth s atmosphere acts as a greenhouse, trapping solar energy. Most of the trapping is due to carbon dioxide and water vapor, which is why they re called greenhouse gasses. Greenhouse Gases: CO 2 Over past 1,000 yrs temperatures were nearly constant until CO 2 emissions increased starting with the industrial revolution. Global Warming Chapter 17: Phase Changes Sequence of increasing molecule motion (and kinetic energy): How do we get from one phase to another? Solid Liquid Gas What are the phases of matter? Familiar phases: Solid (ice) Liquid (water) Gas (water vapor) Perhaps not-so-familiar: Plasma (atoms stripped of electrons) Phase Changes Substances can exist in any of the phases, but behave differently The phase depends on temperature and pressure Phase changes almost always require a transfer in energy 7

8 Phase Changes Energy and Changes of Phase Evaporation/Condensation Liquid! Gas, Gas! Liquid Boiling Liquid! Gas, but not at the surface! Sublimation Solid! Gas (skips liquid) Melting/Freezing Solid! Liquid, Liquid! Solid Chapter 18: Thermodynamics Thermodynamics: the study of heat moving from one body to another Recall: Temperature is a measure of the average kinetic energy of molecules in an object Recall: Absolute zero or 0 K, where there would (theoretically) be no more kinetic energy in the molecules of a substance 0 th Law of Thermodynamics Imagine three systems: A, B, and C If A and B are each in thermal equilibrium with C, then A and B must also be in thermal equilibrium with each other. A C B 1 st Law of Thermodynamics When heat flows to (or from) a system, the system gains (or loses) an amount of energy equal to the amount of heat transferred. Caution: Remember that numerically, ΔQ ΔT! More 1 st Law ΔQ = Δinternal energy + work This is the thermal version of conservation of energy! You can never get more energy out of a system than you originally put in In an adiabatic process, ΔQ = 0 so the Δinternal energy is the same as the work done by the system 8