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Welcome to Physics 7A! Lecturer: Cassandra Paul
Slides will be available online at:
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Logistics Course Website: (click on Physics 7A) Discussion/Lab meet daily Monday-Thursday, and attendance is mandatory. First DL is TODAY! Lecture meets Monday and Wednesday, attendance is also mandatory. Required Book College Physics: A Models Approach Quizzes weekly: Quiz 1 is Wednesday! (Quiz 2 is a week from today.) Reading Assignments Clickers: required and worth 5% of your grade (for participation)
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Setup Clickers Turn Clickers On Select Class:
Scroll down in ‘Setup Menu’ until you see ‘ID’ Press the Green Arrow Enter Student ID
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Test Clickers Have you had Physics before? No, None
Conceptual Physics Class (HS or College) Algebra Based High School Class Algebra Based College Course Calculus Based College Course
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What do you think of when you hear the word Physics?
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What is physics? Can ice be colder than 0°C? Why is the sky blue?
We begin with the child-like wonder about our everyday world. How does a light switch work? How do magnets work? Why does she start spinning so much faster when she pulls her arms and legs in? Why do planets orbit? What is “rainbow” really?
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As Physicists we... Observe phenomena and ask questions about them
Try to explain phenomena using a few principles (models) - We cannot “pick and choose” when an explanation “works” - We must have understanding of when a model is valid and when it is not. (Understanding model limitations is AS important as understanding how the model works!) Physics is taking this approach to explain phenomena in the physical world.
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What is physics 7? Physics 7 is a 3-quarter series of physics classes, typically taken by bio-science and other non-physics science majors. Physics 7A: Energy conservation, thermodynamics, particle models of matter. Physics 7B: Classical Mechanics, rotational motion, fluids, circuits. Physics 7C: Wave phenomena, optics, electricity and magnetism, the atom and modern quantum mechanics.
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How is Physics 7 different?
Less Emphasis on Lecture Less time in lecture than other courses Never EVER tested on things you see ONLY in lecture Models Physics comes from a few principles We will be drawing a lot of diagrams and graphs Emphasis on Conceptual Understanding No multiple choice questions on Quizzes or the Final You are graded on the quality of your argument more than your ability to ‘calculate.’ Most equations will be provided Not Graded on Curve No competition between classmates promotes ‘idea’ sharing Discussion Labs All work is group work You, your classmates will work together to obtain a better understanding of Physics Your TA is your guide, NOT your lecturer
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Physics 7 is BETTER! RESEARCH shows that Students that take Physics 7… Obtain a more conceptual understanding of Physics AND Perform better in later courses Score better on their MCATS …than students who took a traditional version of the course.
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Something to Keep in Mind…
It is your responsibility to learn!
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OK so let’s begin already!
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The first concept in 7A: Energy
What is Energy? Energy is a thing (quantity or state function). It is a property of matter and radiation, and we can think about it as the capacity to do work. You & I contain energy, as do the chairs you sit on and the air we breathe. What are some forms of Energy? Thermal Energy (Having to do with Temperature) Kinetic Energy (movement) Gravitational (potential energy) Can we measure Energy? We can calculate how much energy something has and We can measure the transformation of energy (or change, E). Does this book Have energy?
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Conservation of Energy
Energy cannot be created nor destroyed, simply converted from one form to another. If the energy of an object increases, something else must have given that object its energy. If it decreases, it has given its energy to something else. Energy transfer is done through Heat or Work.
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How can we think about Energy?
… Let’s Use a Model!
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Models Useful way to think of and address questions about phenomena (e
Models Useful way to think of and address questions about phenomena (e.g. Ideal gas model)
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Models in Physics 7A Models can help us organize our thinking, can contain other models, and can be very useful. Models also have limitations: experiment is the final judge. Three-phase model of matter Energy-interaction model Mass-spring oscillator Particle model of matter Particle model of bond energy Particle model of thermal energy Thermodynamics Ideal gas model Statistical model of thermodynamics We start with These two… Show them book fold outs.
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Three Phase Model of Matter (This should be familiar from Chemistry)
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Three-Phase model of Matter
Example H2O Solid: Keeps its shape without a container Liquid: Takes the shape of the (bottom of) the container. Keeps its volume the same. Gas: Takes the shape and volume of the container.
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Three-Phase model of Matter
Example H2O Q How do we change the phase of matter? How do we change the temperature of matter? A By adding or removing energy. Often this energy is transferred from, or to the substance as heat Q.
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Three-Phase model of Matter
Temperature gas l-g coexist TBP s-l coexist liquid TMP solid Energy added or removed
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Example: Melting ice initially at -10C, and bringing it to 15C
Temperature Final gas Initial TBP Ask what is happening to the ice from initial to flat, along the flat line, and flat line to final Where does the energy go?! What sorts of energies are changing? Need a way of talking about where the added energy is going in the flat part… liquid T TMP T const T solid Energy added
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Energy Interaction Diagrams Based on the energy interaction model, it shows you how energy is transferred, how energy is conserved between energy systems.
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Energy-Interaction Model
Energy systems: There are many different types of energies called energy systems: Emovement (KE) Ethermal Ebond Espring Eelectric Egravity For each energy system, there is an indicator that tells us how that energy system can change. Ethermal: indicator is temperature Ebond: indicator is the initial and final phases
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Energy interaction diagrams - closed
Ea Eb Ec Conservation of Energy The total energy of a closed physical system must remain constant. In other words, the change of the energies of all energy systems associated with the physical system must sum to zero. Change in system energy = ∆Ea + ∆ Eb + ∆ Ec = 0
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Energy interaction diagrams - open
Ea Eb Ec Energy added Energy removed Conservation of Energy The change of the energies of all energy systems associated with an open physical system must sum to the net energy added/removed as heat or work. Change in system energy = ∆Ea + ∆ Eb + ∆ Ec = (Energy added) - (Energy removed) = Q+W
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Back to the example… Melting ice initially at -10°C, and bringing it to 15°C To set up the model: Define system Define interval What indicators are changing? What energies are changing? How are they changing? Is this an open or closed system? What (if anything) is entering/leaving the system? Write Energy Conservation Equation Work out problem on the board with help from the class
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The Energy Interaction Model
How can we model how much Energy is needed to melt ice initially at -10C, and bring it to 15C? System: H2O Initial: Solid (Ice) at -10°C Final: Liquid (Water) at 15°C Ice Mixed Water Ethermal Ebond Ethermal HEAT ml T T T I: T=-10°C F: T=0°C I: all solid F: all liquid I: T=0°C F: T=15°C + + + + ΔEths + ΔEbond + ΔEthl = Q
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Condensing Steam initially at 100°C to a final temperature of 40°C
TBP How many Energy systems? TMP Energy added or removed
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Condensing Steam initially at 100°C to a final temperature of 40°C
To set up the Energy Interaction Model: Define system Define interval What indicators are changing? What energies are changing? How are they changing? Is this an open or closed system? What (if anything) is entering/leaving the system? Write Energy Conservation Equation
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Condensing Steam initially at 100°C to a final temperature of 40°C
System: H2O Initial: Gas (steam) at 100°C Final: Liquid (Water) at 40°C Mixed Water Ethermal Ebond HEAT mg T I: T=100°C F: T=40°C I: all gas F: all liquid ΔEthl + ΔEbond = Q
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Next lecture is Wednesday
Quiz 2 will cover today’s lecture, and Discussion/Lab 1 material INCLUDING FNT (For Next Time) questions.
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