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23 Cards in this Set

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Equilibrium
-no translational or angular acceleration.
-a system is in equilibrium if the translational velocity of its center of mass and angular velocities of all its parts are constant
-the net force acting on a system in equilibrium is ZERO.

Fupward = Fdownward
Frightward = Fleftward
Static equilibrium
-If all velocities in a system are zero.
Dynamic equilibrium
-If any velocities are nonzero, but all velocities are constant.
Systems not in equilibrium
-this means that the center of mass is accelerating translationally or its parts are accelerating rotationally.

Steps for facing a problem that is not in equilibrium:

1. write the equations as if the systems are in equilibrium
2. before solving, add 'ma' to the side with less force.
Torque
-a twisting force, a vector but the MCAT allows us to think of torque as clockwise or counterclockwise.
-When the lever arm is used, equation for torque is:

T =Fl

F = the force applied
l = is where the position vector is form the point of rotation to the point where the force acts at 90 degrees. (lever arm)
Lever arm
-a position vector that is from the point of rotation to the point where the force acts at 90 degrees.
Units of energy
-Joule
-electron volt
Mechanical energy
-the kinetic energy and potential energy of macroscopic systems.
Kinetic energy (K)
-the energy of motion

K = 1/2mv^2
Potential energy (U)
-the energy of position
-all potential energies are position dependent.
Gravitational potential energy (Ug)
-the energy due to force of gravity

Ug =mgh
Elastic potential energy Ue
-the energy due to the resistive force applied by a deformed object.

Ue = 1/2kdelta(x)^2

k = hooke's law constant for the object
x = displacement from the object's relaxed position
Law of Conservation of Energy
-since the universe is an isolated system, the energy of the universe remains constant
Work
-the transfer of energy via force

W = Fdcos(theta)

where
F = force
d = displacement of the system
theta = angle between F and d
Heat
-the transfer of energy by natural flow from a warmer body to a colder body
Frictional forces
-an exception to the work equation because frictional forces change internal energy as well as mechanical energy.
Equation describing total energy transfer due to forces and none to heat
W = deltaK + deltaU + deltaEi
Equation describing total energy transfer due to forces and none to heat or friction
W = deltaK + deltaU
Conservative Force
-mechanical energy is conserved within the system
-When a force acts on a system and the system moves from point A to point B and back, the total work done by the force is zero and it is conservative.
-the energy change is the same regardless of the path taken.
Law of Conservation of Mechanical Energy
-States that when only conservative forces are acting, the sum of mechanical energies remains constant.

K1 + U1 = K2 + U2 or
0 = DeltaK + deltaU
Nonconservative forces
-forces that change mechanical energy of a system when they do work
examples:
-friction
-pushing and pulling of animals

W = delta(K) + delta(U)
Kinetic frictional forces
-increase the internal energy of the systems to which they are applied
-does negative work on a sliding box

FkD = delta(K) + delta(U)
Power
-Rate of energy transfer
-unit of power is the Watt (W) which is equivalent to J/s.

P = delta(E)/t

equation for instantaneous power due to a force:

P=Fvcos(theta)