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V=IR I=V/R R=V/I
Votlage = Resistance x Current
Curcuits Parallel Circuits
Both ends of the components are connected together.
There are multiple paths for current to flow.
Components are connected end-to-end
There is only a single path for current to flow Mechanical Advantage Ideal -study of the effects of work, heat, & energy on a system, movement of thermal energy Thermal energy- kinetic energy that transmits from one object to another due to temp. difference [joules] How materials are classified Insulators vs. Conductors
materials that allow electron flow
generally have four valence electrons or less
materials that do not allow electrons to flow
generally have more than four valence electrons
The movement of electrons electricity is the flow of electrons
If a material permits that flow determines weather it is an insulator or a conductor
there are three important measurements in the flow of electricity
amps Characteristics of a Parallel Circuit
The voltage across every parallel component is equal.
The total resistance (RT) is equal to the reciprocal of the sum of the reciprocal:
The sum of all of the currents in each branch (IR1 + IR2 + IR3) is equal to the total current (IT). This is called Kirchhoff’s Current Law.
Characteristics of a series circuit
The current flowing through every series component is equal.
The total resistance (RT) is equal to the sum of all of the resistances (i.e., R1 + R2 + R3).
The sum of all voltage drops (V1 + V2 + V3) is equal to the total applied voltage (VT). This is called Kirchhoff’s Voltage Law. Power P= The properties of electrical circuits Current
measured in amps
measures the current of electricity or how much charge is passing a single point in a given amount of time
conventional flow vs. electron flow
convention assumes all charge is leaving the positive side when in reality it does not
engineers use conventional flow
measured in volts
its is the pressure of the current or the energy of the electrons
Measured in Ohms
it is how much the electron flow is limited UNIT 1 REVIEW Work, Energy & Power By: Matt Conti & Morgan Ritter Simple Machines Actual -no friction -IMA= DE ___ DR DE= distance of effort DR= Distance resistance -Friction -AMA= FR --- FE FR= Force of resistance FE= Force of effort MA>1 MA<1 -Less effort -greater
distance -More effort -less distance Levers -3 classes
-rigid bar used to exert pressure 1st class -fulcrum located in middle MA <1 >1 2nd class -fulcrum located on end MA>1 3rd class -fulcrum located on end effort resistance Wheels and Axles DE= pi(diameter of effort)[wheel or axle]
DR= pi(diameter of resistance)[axle or wheel] MA<1 Moment -turning effect of a force m= d * F Static Equilibrium -effort and distance moment are equal Efficiency -ratio of useful energy output to total energy input %= --- AMA IMA ME=MR FR * DR= FE * DE -a wheel is a lever arm fixed to an arm shaft(axle) both forces will travel in a circle C= d*pi C=2*r*pi d= 6 d= 25 IMA= DE pi DR pi ------ = 25 pi ----- 6 pi = 4.16667 Pulleys a lever consisting of a wheel with a groove in its rim which is used to change direction & magnitude of a force exerted by a rope Fixed Pulley -1st class lever
-changes direction of force http://www.google.com/imgres?sa=X&biw=1517&bih=714&tbm=isch&tbnid=PE0Lp6g8XUfDkM:&imgrefurl=http://chestofbooks.com/crafts/metal/Applied-Science-Metal-Workers/38-Block-And-Tackle.html&docid=Ra6-8rWft534XM&imgurl=http://chestofbooks.com/crafts/metal/Applied-Science-Metal-Workers/images/Fig-17-A-Fixed-Pulley.jpg&w=141&h=324&ei=03ejUZDNFtOo4APIroDwBw&zoom=1&ved=1t:3588,r:15,s:0,i:207&iact=rc&dur=4388&page=1&tbnh=184&tbnw=80&start=0&ndsp=27&tx=39&ty=87 Movable Pulley -2nd class lever
-IMA= 2 http://www.google.com/imgres?biw=1517&bih=714&tbm=isch&tbnid=bgOkrC1hfxiZ1M:&imgrefurl=http://library.thinkquest.org/CR0210120/Magnificent%2520M%2520P.html&docid=iENpe6-uFsNZVM&imgurl=http://library.thinkquest.org/CR0210120/Media/M%252520P%252520Picture&w=163&h=264&ei=6HijUYKTNc-44APz6oGAAg&zoom=1&ved=1t:3588,r:6,s:0,i:177&iact=rc&dur=379&page=1&tbnh=208&tbnw=128&start=0&ndsp=26&tx=60&ty=78 Block and Tackle -1 rope goes through several pulleys http://www.google.com/imgres?biw=1517&bih=714&tbm=isch&tbnid=Bg0GWWmiDiZm0M:&imgrefurl=http://www.cstephenmurray.com/onlinequizes/physics/simplemachines/pulleybasics.htm&docid=J2mC85EbcEpFyM&imgurl=http://www.cstephenmurray.com/onlinequizes/physics/simplemachines/simplemachinepictures/pulley4ropes.gif&w=153&h=306&ei=i3qjUZ6OLdLI4APUyIDAAQ&zoom=1&ved=1t:3588,r:4,s:0,i:171&iact=rc&dur=1617&page=1&tbnh=186&tbnw=93&start=0&ndsp=27&tx=48&ty=110 -force direction stays constant Pulley IMA -# of strands opposing the force of the load Pulleys in Combination -separate ropes or cables IMA(total)= IMA * IMA * IMA https://www.google.com/search?q=combination+pulleys&source=lnms&tbm=isch&sa=X&ei=oH6jUdHgNfPK4AO1mYDYBw&ved=0CAoQ_AUoAQ&biw=1517&bih=714# Inclined Planes Flat surface set at an angle/incline with no moving parts IMA= DE ----- DR AMA= FR FE ----- DE= L
DR= H L H Wedges -a moving inclined plane
-used for splitting/tightening IMA= ----- DE DR AMA= FR FE ----- H L DE= L
DR= H Screws Two components: inclined plane wrapped in a cylinder, forms path & pitch wheel & axle used to create rotary motion Properties -changes rotary motion into linear motion -used as a threaded fastener -Large MA -Large amount of friction loss IMA= DE ----- DR = circumference --------------------- pitch = 2*pi*r -------- p DE= circumference DR= linear distance traveled(pitch) example: What is the pitch of a 1/4 20 UNC bolt? 1 ---- 20 p= Compound Machines when one simple machine is used after another the mechanical advantage multiplies example IMA[total] = IMA[pulley] * IMA[lever] = # number of strands * DE ----- DR Work(W) -The product of the force applied to an object over a distance in which the object travels as an result W= F*d Joule(J) -Base unit of work - 1 joule= 1 newton * 1 meter J=N*m Energy -ability to do work light, heat, mechanical, chemical, & electrical forms of energy can all be used to exert a force for a distance Forms of Energy Potential Energy- stored energy, usually referring to gravitational energy Kinetic Energy- energy of motion Energy can't be created or destroyed but it can change from one form to another Energy Conversion -changing one form of energy to another Energy Efficiency- the ratio of the useful energy delivered by a dynamic system to the energy supplied to it Efficiency %= P[out] ------ P[in] * 100 examples: fossil fuels chemical heat mechanical electrical wind turbines kinetic mechanical electrical nuclear nuclear heat mechanical electrical -rate at which work is performed or energy is expended work ---- time watt- base unit of power 1 watt= 1 joule of work per second Types electrical power- use electrical energy
mechanical power- uses mechanical energy [linear,rotary]
fluid power- uses energy transferred by liquids[hydraulics]
and gases[pneumatics] Thermodynamics What is it? Temperature- average kinetic energy of particles in an object [degrees] Matter is made of molecules in motion temperature, motion temperature, motion Absolute zero- when all kinetic energy is removed from an object Equilibrium -achieved when two objects within a system reach the same temp. -system loses ability to work as well Zeroth Law of Thermodynamics if two systems are separately found to be in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other Heat transfer Convection, conduction & radiation 100% efficiency can't be achieved ALL processes can't be reversed 1st Law of Thermodynamics Law of energy conversation applied to a thermal system -Thermal energy can change form and location, CAN"T BE DESTROYED! -Thermal energy when thermal energy is added or by performing work in the system 2nd Law of Thermodynamics Thermal energy flows from hot to cold entropy- measure of how evenly distributed heat is in a system order disorder Convection transfer of thermal energy by movement of fluid fluid heats & becomes less dense then rises Conduction transfer of thermal energy within an object or between objects from molecule to molecule Radiation process when energy is transmitted through a medium(ex. empty space) as electromagnetic waves Thermal Energy Transfer Equations see reference sheet ex. A piece of copper steel (specific heat= 490 J/kg*K) has a mass of 300 g. If it is heated to 150 degrees Celsius, then plunged into 4.00 kg water(specific heat=4180 J/kg*K) at 20 degrees Celsius, what will be the final temperature at equilibrium? Answer Q[water]=Q[copper] Q=mCp T .3 kg*490(423-Tf)=4*4180(Tf-293) 62181-147Tf=16720Tf-4898960 4961141=16867Tf 294 K=Tf R-Value -Thermal resistance of a material Measures the material's ability to resist heat R-value, resistance R= 1 ---- U U-Value Coefficient of heat conductivity Measures a material's ability to conduct heat U= P ----- A T P=rate of energy transfer A= area of thermal conductivity T= Difference in temperature Stefan's Law All objects lose and gain thermal energy by electromagnetic radiation Pnet= Ae(T2^4-T1^4) P=radiated energy transfer =Stefan's constant= 5.6696*10^-8 A= Area W ------ m^2*k^4