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32 Cards in this Set
- Front
- Back
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Equilibrium
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No translational (straight line) or angular (rotational) acceleration
All velocities are constant Does not mean motionless Sum of all forces acting on system equal to zero (ie. Net Force = 0) Fup = Fdown Fright = Fleft |
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Static Equilibrium
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If all velocities are zero
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Dynamic Equilibrium
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If all velocities are constant and nonzero
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Translational Equilibrium
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Upward forces equal downward forces and rightward forces equal leftward forces
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System not in equilibrium
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Center of mass of system is accelerating translationally or its parts are accelerating rotationally
Sum Forces = ma 1. Write equations as if system in equilibrium 2. Add "ma" to side with less force (all numbers should be positive) |
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Torque
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Twisting force, clockwise or counterclockwise
T = Frsin0 F: force r: position (distance from point of rotation to point of application of force) T = Fl F: force l: lever arm 0: angle between force and position vectors |
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Point of Rotation
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Any fixed point of your choosing
Center of mass |
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Lever arm (l)
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Position vector is from point of rotation to point where force acts at 90 degress
T = Fl |
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How to solve Torque problems:
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1. Fup = Fdown
2. Fright = Fleft 3. Tclockwise = Tcounterclockwise |
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Energy
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Capacity to do work
Units: 1. joules (J) = kg m^2/s^2 2. electron-volt (eV) Scalar 2 types: 1. mechanical 2. nonmechanical |
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Mechanical Energy
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Kinetic energy and potential energy of macroscopic systems (system you can examine without a microscope)
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Kinetic Energy (K)
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Energy of motion
Any moving mass has kinetic energy K = (1/2)mv^2 |
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Potential Energy (U)
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Energy of position
Several types: 1. gravitational potential energy (Ug) 2. elastic potential energy (Ue) 3. electric potential energy (Uelectric) |
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Gravitational Potential Energy (Ug)
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Energy due to force of gravity
Ug = -Gm1m2/r G: universal gravitational constant m1 & m2: 2 masses r: distance from 2 centers of gravity neg sign: indicates energy decreases as distance decreases |
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Gravitational Potential Energy near Earth's surface
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Ug = mgh
m: mass g: gravity h: height of object |
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Elastic Potential Energy (Ue)
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Energy due to resistive force applied by deformed object
Follows Hooke's Law Ue = (1/2) k (change in x^2) k: Hooke's law constant change in x: displacement of object from relaxed position |
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Law of Conservation of Energy
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Since universe is an isolated system (mass nor energy is exchanged with environment), the energy of universe remains constant
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2 types of energy transfer:
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1. work (W)
2. heat (Q) |
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Work
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Transfer of energy via a force
Scalar Measured in units of energy (joules) W = Fdcos0 (for all forces except friction) F = force d = displacement 0 = angle between F & d |
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Heat (Q)
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Transfer of energy by natural flow from a warmer body to a colder body
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Frictional Force
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Change internal energy as well as mechanical energy
Therefore are not forces which can do work |
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Work = forces & no heat
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W = (change in K) + (change in U) + (change in Ei)
Ei = internal energy, frictional energy |
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W = forces & no heat & no friction
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W = (change in K) + (change in U)
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Work-Energy Theorem
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W = (change in K)
Only true when all energy transfer results on in change of K |
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1st Law of Thermodynamics
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Energy is always conserved
Change in E = W + Q |
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Conservative Force
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Mechanical energy is conserved within system
Net Work = zero Energy change is the same regardless of path taken by system Strength dependent only on position Have potential energy associated with them Do not change mechanical energy Do not change temperature or Ei of object Types: 1. gravitational forces 2. hooke's law forces 3. electrical forces 4. magnetic field forces |
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Law of conservation of mechanical energy
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When only conservative forces are acting, the sum of mechanical energies remains constant
K1 + U1 = K2 + U2 (no heat, only conservative forces) 0 = (change in K) + (change in U) (no heat, conservative forces only) |
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What work is done by a conservative force?
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Consider conservative force is not part of system
1. W = Fdcos0 2. Calculate change in Ug 3. W = (Change in K) + (Change in U) + (Change in Ei) (do not include calculation of conservative force being questioned) Technically conservative forces do not do work because energy is never lost no gained by system |
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Nonconservative forces
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Forces that change mechanical energy of a system when they do work
types: 1. kinetic frictional forces 2. pushing and pulling forces W = (change in K) + (change in U) (except for frictional forces, no heat) |
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Kinetic frictional forces
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Increase internal energy of systems to which applied
Amount of work done by such a force does not go into changing mechanical energy W = (Change in K) + (change in U) = (Change in Ei) K = Ei |
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Power
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Rate of energy transfer
Unit: watt (W) = J/s P = (change in E)/t t: time E: energy = W + Q Rate at which force does work P = W/t W: work t: time |
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Instantaneous Power due to Force
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P = Fvcos0
0: angle between F & v v: velocity F: force Scalar |
