Notes-2 from Chapter 8, Thinking Like an Engineer

1. The Six Types of Energy and the Units used

   Type of Energy	Units	Explanation
   Work (W)	W = Fd	-Energy used by exerting a force (F) over a distance (d) -Measured in joules (J)  J = Nm      (1 Newton meter) -Alternative measurement: ft (lb_force)
   Potential Energy (PE)	PE = mgh	-type of work -moving a weight (force; mass times gravity) a vertical distance (height; h)
   Kinetic Energy (KE)	KE_translational = 1/2mv^2 KE_rotational = ½ I w^2 Total KE = KE_t + KE_r	-characteristic of an object in motion -KE translational: If a constant force is applied to an object then the object’s acceleration will remain constant as proven by F=ma and the object’s velocity will increase in consistent intervals -KE rotational: Rotating objects also have kinetic energy whether they move along a distance or not. EX) Bicycle wheel- when in motion it does not move a distance but it does rotate It is calculated using angular velocity (Greek letter omega; w) which is the object’s rotational speech given in units of radians per second and the moment of inertia (I) which depends on mass and geometry of object -Total KE equals KE translational and KE rotational values
   Thermal Energy	Q = mCT	-Heat (Q) -Thermal energy is associated with a change in temperature (T), the mass of an object (m) and the specific heat of the object (C). -Can be expressed in British thermal units (BTUs) and calories BTU:  “amount of heat required to raise the temperature of one pound-mass of water by one degree Fahrenheit” Calorie: “amount of heat required to raise the temperature of one gram of water by one degree Celsius”

2. Power

   Power (W)

   W = J/s

   -Power (watts; W) is described as energy (joules; J) per time (seconds; s) -Power is a rate -Alternative measurement: horsepower (hp); described as the power used to replace the work that can be completed by a horse EX) Running a mile in 5 minutes versus running a mile in 10 minutes Running a mile in 5 minutes will require you to produce energy in a smaller amount of time (comparatively more power is generated) Running a mile in 10 minutes will require you to produce the same amount of energy in a longer amount of time (comparatively less power is generated)
3. Electric Concepts (electric charge, electric current, voltage, electric resistance, electric power)
   
   
   

   Electrical Concept	Units	Explanation
   Electric Charge Symbol: (Q)	C = As	-In basic terms, electric charge is measured by the charge “e”      Proton e = +1      Electron e = -1 -More generally, electric charge in measured in coulombs (C)      C = Amperes * time in seconds      1 coulomb = the total      charge of 6.24 x 10^18      protons -Subatomic particles experience repulsive (like-charge) and attractive (opposite charge) forces as described by Coulomb’s Law which is a function of the charge of two objects and the distance between the charges (r)  -K_e is coulomb’s constant 9 x 10^9 N m^2 / C^2
   Electric Current Symbol: I	A = C/s	-movement of charges in a solid material -it is assumed that charges move from the negative terminal to the positive terminal -measured in amperes (A), which represent the movement of one coulomb (C) of charge past any given point per second (s) -circuit diagrams denote the direction of the charges
   Voltage Symbol: V	V = J/C	-a measure that quantifies the work required to move an electric charge in the vicinity of other electric charges -measured in volts (V) which equals 1 joule/ 1 coulomb or the energy required to move a coulomb of charge one place to another. The voltage between these two places in one volt.      W = Fd      W = QV -PE in voltage is evident when charges are surrounded by like charges -KE in voltage is evident when charges are surrounded by opposite charges -need to note assumed polarity of a voltage (which end of device is more positive); used to track whether energy is being stored or released
   Electrical Resistance Symbol: R	M = V/A	-measures how difficult it is to move charges through a material -measured in ohms (Greek letter omega; symbol won't show up so for our purposes the symbol is M) which is defined as one volt (V) per ampere (A) In other words, if a 1 volt battery was connected to a device having a resistance of one ohm, then one ampere of current would flow through the device. “Resistance relates the voltage across a device to the current through the device.” -Electric current travels through a substance -The voltage is the difference between the forces exerted on a charge from both ends of a device depending on the charge of each end of the device -related to current and voltage by Ohm’s Law -To maintain a constant current through a resistance requires a voltage proportional to the resistance -Current is inversely proportional to resistance. If voltage increases, current increases. If resistance increases, current decreases because the voltage has a harder time pushing the charges through the device.
   Electric Power Symbol: P	P = VI                (V=voltage) P = VA                  (V=volts) P = (J/C)*(C/s) P = J/s	-Measures energy released and stored in electrical charges due to voltage and current -Electrical power is a function of the work required to move an electrical charge in the vicinity of other charges (voltage; V) and the movement of charges in a solid material (amperes; A) -Electrical power is a rate

   
   
4. Discuss resistors
   
   
   Resistor: An object that has resistance to electrical current
   The electrical power that is stored in a resistor due to charges being near like charges is usually converted to heat.
   Equations that are used to solve for the amount of power absorbed by a resistor:
   P = VI = (IR) I = I^2R
   P = VI = V(V/R) = V^2/R
   Specifications: resistance and wattage
   
   
5. Discuss capacitors
   
   
   Formed by putting two conducting, low resistance plates close to one another, each with a wire connected to it, and separating them with an insulator that has extreme resistance
   When a current made of electrons is run through one of the two plates, electrons begin to build up on that plate because they cannot penetrate through the insulator material. The build up of electrons repels the negative charges on the opposite plate, which leaves an overall positive charge on the opposite plate. This gives the impression that the current has traveled through the insulator, but it hasn't. The charge stored in a capacitor is proportional to the voltage across it: Q = CV  
   C is a proportionality constant
   Referred to as capacitance (C)

   Measured in farads (F)

   units of F: coulombs per volt

   F = C/V

   If a capacitor stores a charge of one coulomb and the resulting voltage is one volt, then the capacitance is one farad. 

   
   The energy stored in a capacitor: E = 1/2CV^2 (formula similar to kinetic energy)
   Specifications: capacitance and maximum voltage
   
   6. Inductors
   
   Generally an inductor is simply a coil or wire
   If a current is run through a wire, it generates a magnetic field.
   If a wire is in an environment with a changing magnetic field, a current is induced in the wire. (This is really interesting. I kind of want to try to do this.)
   Inductors store energy in the form of magnetic fields
   If the source of a current pushing current through a wire is removed, the magnetic field will collapse. However, the collapsing of the magnetic field (changing magnetic field) induces a current.
   Inductance (L)
   

   Measured in henrys (H)

   H = Vs/A = M s = J/A^2

   Voltage across inductor:
   

   V = L (dI/dt)                (dI/dt) = rate of change of current 

   
   The energy stored in an inductor: 1/2LI^2 (formula similar to kinetic energy)
   Specifications: inductance and max current