Work and Energy Flashcards
Energy
systems ability to do work
Kinetic Energy
energy of motion
KE = 1/2 mv^2
v is NOT velocity, its SPEED
not dependent on velocity vector
Joule
unit of energy
1J = 1 kg m^2 / s^2
Potential Energy
energy associated given an objects position in space
potential to do work
ex: chemical/electrical
2 Types for Movement: Gravitational and Elastic
Gravitational Potential Energy
depends on an objects position with respect to datum
U = mgh
Datum
level identified as ground or the zero potential energy position
Elastic Potential Energy
springs and other elastic systems
when a spring is stretched or compressed from its equilibrium length, the spring has elastic potential energy
U = 1/2 k x^2
x = magnitude of displacement
k = spring constant
Total Mechanical Energy
summation of an objects potential and kinetic energies
E = U + K
First Law of Thermodynamics
accounts for conservation of mechanical energy, meaning energy is neither created nor destroyed
NOT ALWAYS CONSTANT as other forms of energy not always accounted (thermal from friction)
Conservative Forces
path independent and do not dissipate energy
have potential energy associated with them
gravitational/electrical
Methods of Determining Conservative Forces
1) object moves and comes back to its starting point with a net change of 0 for energy
2) other method is when an object goes from one point to another, the energy change is equivalent regardless of the path taken
Nonconservative Forces
friction, air resistance, viscous drag
path dependent
W = delta E = deltaU + deltaK
work done by nonconservative forces will be exactly the amount of energy lost from system
Work
process of how energy is transferred
W = Fd = Fdcos(theta)
F and d are magnitude of force and distance
only forces parallel or antiparallel to the displacement vector will do work
Piston
as gas expands, it pushes up on piston exerting a force to cause it to go up and increase the volume of the system
when gas is compressed, the piston pushes down on the gas, exerting a force to decrease volume of the system
Work is done when the volume of the system changes due to an applied pressure
PV Curve
Pressure is Y, Volume is X
work done can be determined by finding the area under the curve
As gas expands, work done is _____ and when a gas is compressed, work done is ____.
If volume stays constant as pressure changes, then ___ work is done, This is an _______ process.
If pressure remains constant and the volume changes, then the area under curve (work) is
W = P deltaV.
This is a _______ process
positive, negative
zero
isochoric/isovolumetric
isobaric
Power (watts)
rate at which energy is transfered from one system to another
P = W/t = delta E / t
W = work
Work Energy Theorem
direct relationship between the work done by all forces acting on an object and the change in kinetic energy of that object
Wnet = deltaK = Kf - Ki
Mechanical advantage
any device that allows work to be accomplished through a smaller applied force
ratio of magnitude of force exerted ON an object BY a simple machine to the force actually applied ON the simple machine
Fout / Fin
Simple machines
increase mechanical advantage
wedge, wheel and axle, lever, pulley, screw
Efficiency
Efficiency = Wout/Win = (load)(load distance) / (effort)(effort distance)
