Unit 7- Energy Physics on-conservation-of-en/ on-conservation-of-en/

Bell ringer 3/31 What is energy?What is energy? Ability to cause changeAbility to cause change The ability to do workThe ability to do work Mechanical energy is the energy that is possessed by an object due to its motion or due to its positionMechanical energy is the energy that is possessed by an object due to its motion or due to its position Transferred from place to place or from object to objectTransferred from place to place or from object to object Can’t be created nor destroyed- Law of conservation of energyCan’t be created nor destroyed- Law of conservation of energy This E__ notation It stresses the universal nature of energy - it’s all energy. In this energy unit, we will use E__ to indicate the modes of energy storage involved rather than discuss “types of energy”. Symbols of energy transfer (across the system boundary) will be Q -heating as energy transfer due to temperature difference R (radiating), W -working as energy transfer due to interactions with external agents

Conservation of energy Richard Feynman lecture ess.com/2012/09/24/day- 12-feynmans-lecture-on- conservation-of-en/ ess.com/2012/09/24/day- 12-feynmans-lecture-on- conservation-of-en/ ess.com/2012/09/24/day- 12-feynmans-lecture-on- conservation-of-en/ ess.com/2012/09/24/day- 12-feynmans-lecture-on- conservation-of-en/ Money analysis Law of Conservation of Energy- state that the algebraic sum of these energy storage changes and transfers must add up to zero, accounting for all changes relative to the system.

Storage of Energy. An object that has motion - whether it is vertical or horizontal motion - has kinetic energy. Ek - kinetic energy, defined as the energy of motion. An object that has motion - whether it is vertical or horizontal motion - has kinetic energy. is the stored energy of position or height possessed by an object. Eg - gravitational potential energy, is the stored energy of position or height possessed by an object. is the energy stored in elastic materials as the result of their stretching or compressing. Eel - elastic potential energy-again, is the energy stored in elastic materials as the result of their stretching or compressing. Eint - energy stored internally as the kinetic or interaction energy of the constituent particles Ech- energy due to attractions of atoms within molecules. These attractions are described as chemical bonds because they are considerably stronger than those between molecules and last much longer. Ech- energy due to attractions of atoms within molecules. These attractions are described as chemical bonds because they are considerably stronger than those between molecules and last much longer.

Storage of Energy Energy nameSymbolEnergy is Stored in kineticEKEK Motion of the object Gravitational potential EgEg gravitational field Elastic potential E el Spring (by stretching/compressing it) ChemicalE ch Chemical bonds Internal/interact ive E int In the motion of molecules

energy potentialgravitationalelastickineticChemical Interactive/ internal

There are three energy transfer modes and these are described as gerunds to emphasize that they are processes rather than real things apart from energy.There are three energy transfer modes and these are described as gerunds to emphasize that they are processes rather than real things apart from energy. They are working (W), heating (Q) and radiating (R).They are working (W), heating (Q) and radiating (R). These transfer modes operate to move energy between the system and the surroundings. It is very important to recognize that such energy transfers affect both the system and the surroundings.These transfer modes operate to move energy between the system and the surroundings. It is very important to recognize that such energy transfers affect both the system and the surroundings. Energy doesn’t mysteriously appear or get lost.Energy doesn’t mysteriously appear or get lost. 3 transfers

Energy storage Notes All energy interactions can be characterized as energy transfer mechanisms or energy storage modes Energy storage modes - kinetic, potential and internal energies (Ek, Eel, Eg, ∆Eint, Echem ) Energy transfer- heat, work, radiating (Q, W, R) All energy interactions can be characterized as energy transfer mechanisms or energy storage modes Energy storage modes - kinetic, potential and internal energies (Ek, Eel, Eg, ∆Eint, Echem ) Energy transfer- heat, work, radiating (Q, W, R) Energy storage Q W R Conservation of energy- energy can not be created nor destroyed, only transferred/or stored from one form to another This will be done using pie graphs

Working (referred to as work by the physicists as if it is something different from energy) is the way in which energy is transferred between macroscopic (large enough to be seen) objects that exert forces on one another. Working (referred to as work by the physicists as if it is something different from energy) is the way in which energy is transferred between macroscopic (large enough to be seen) objects that exert forces on one another. It is OK to calculate how much “work” one object does on another so long as you do not think that work is something an object stores. It is OK to calculate how much “work” one object does on another so long as you do not think that work is something an object stores. Working

Heating - way in which energy is transferred by the collisions of countless microscopic objects. Heating - way in which energy is transferred by the collisions of countless microscopic objects. Energy is always transferred from the “hotter” object (one in which the molecules have greater Ek) to a colder one (one in which the molecules have lower Ek). Energy is always transferred from the “hotter” object (one in which the molecules have greater Ek) to a colder one (one in which the molecules have lower Ek). If all the molecules have the same mass, then the “hotter” ones are moving faster than the “colder” ones. If all the molecules have the same mass, then the “hotter” ones are moving faster than the “colder” ones. It’s OK to say that you heat an object – just not that the object stores heat. It’s OK to say that you heat an object – just not that the object stores heat. heating

Radiating is the process in which energy is transferred by the absorption or emission of photons (particles of light). Radiating is the process in which energy is transferred by the absorption or emission of photons (particles of light). A light bulb filament can be heated to the point that it glows; this is the emission of photons that carry energy away from the filament. You can be warmed by light from the sun as the photons transfer energy to you. A light bulb filament can be heated to the point that it glows; this is the emission of photons that carry energy away from the filament. You can be warmed by light from the sun as the photons transfer energy to you. Radiating

How to make an energy pie graph 1.Define your system – by drawing a dashed circle around it (the broader the better) or listing the items involved 2.Storage- At each step draw a circle a)Label the circle based on what initial energy the system has stored b)Label the next circle(s) based on what energy and amount it has stored c)Label the last circle based on what energies and amounts the system ends with 3.Transfer- at each step draw an arrow if energy is transferred a)If energy is taken out have the arrow point out of the system i.The next circle should then get smaller b)If energy is added have the arrow point into the system i.The next circle should then get bigger

Example 1-Dropping a ball from chest height 1.System- ball, earth, & ground 2.

Example 2- sliding a Box on the Ground assume there is friction 1.System- box, ground, and air 2. v=>>>> v=>> v= 0

Example 3- sliding a Box on the Ground assume there is friction 1.System- block only 2. v=>>>> v=>> v= 0

Example 4- Bow and arrow 1.System-bow, arrow, air 2. v=>>>> v=>>v= 0

Bell ringer 4/1 When a falling object stops, what happens to it’s energy?When a falling object stops, what happens to it’s energy? Answer- Because of the law of conservation of energy, the total energy of the system stays constant. Before it’s dropped the ball has potential energy, this is then changes to moving energy as it approaches the floor. When it hits the ground, some energy is transferred as heat, friction, and sound. The ball bounces back up, but doesn’t reach the same original height. The process starts over again until all the remaining energy is transferred as heat, fiction, and sound.

Lab- Elastic energy Tria l # Mass in g Mass in kg Force= mass*ag x in cm

Bell ringer 4/3 What did the slope of the F vs. X graph mean?What did the slope of the F vs. X graph mean? What did the area under the F vs. X graph mean?What did the area under the F vs. X graph mean?

Post Lab Springs are a special instance of a device that can store elastic potential energy due to either compression or stretching.Springs are a special instance of a device that can store elastic potential energy due to either compression or stretching. A force is required to compress a spring; the more compression there is, the more force that is required to compress it further.A force is required to compress a spring; the more compression there is, the more force that is required to compress it further. For certain springs, the amount of force is directly proportional to the amount of stretch or compression (x); the constant of proportionality is known as the spring constant (k).For certain springs, the amount of force is directly proportional to the amount of stretch or compression (x); the constant of proportionality is known as the spring constant (k). Such springs are said to follow Hooke's Law. If a spring is not stretched or compressed, then there is no elastic potential energy stored in it. The spring is said to be at its equilibrium position.Such springs are said to follow Hooke's Law. If a spring is not stretched or compressed, then there is no elastic potential energy stored in it. The spring is said to be at its equilibrium position. There is a special equation for springs that relates the amount of elastic potential energy to the amount of stretch/compression and the spring constant.There is a special equation for springs that relates the amount of elastic potential energy to the amount of stretch/compression and the spring constant. The equation isThe equation is

Bell ringer 4/4