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static equilibrium
zero velocity

dynamic equilibrium
velocity is not zero

Is equilibrium motionless?
NO!
just, some of all forces acting on the system = 0

straight acceleration (not in equilibrium)
What is the equation?
∑F = ma
 1. write equation as if sys. were in equilibrium
 2. add "ma" to side with less force

Example: F_{down} due to gravity
F_{up} due to air resistance
F_{down} > F_{up}, so
F_{down} = F_{up} + ma

What does this mean?
In order to be in equilibrium F_{up} must be increased by ma

Torque (equation)
t = F x r x sin

Torque (equilibrium)
0 net torque
T_{clockwise} = T_{counterclockwise}

static equilibrium
F_{up} = Fdown

If force is at the point of rotation, what is the torque?
0

board hanging on a string, in equilibrium
 F = mass of the board
 at the center of mass

Units of energy
 (J) for macroscopic sys
 (eV) microscopic sys

forms of mechanical energy
 kinetic energy
 potential energy

What is kinetic energy?
What is the equation for kinetic energy?
energy of motion
1/2 mv^{2}

