PHY 2020
Fall 2015
Useful Equations #5
g = 10 m/s2
1 N = 1 kg m/s2
If a = 0 and v =constant, then d = vt
If a =constant then v = at, and as a consequence d = 21 at2 and t =
p
2d/a
F~ = m~a
P.E.= mgh
K.E.= 21 mv 2
Momentum= p~ = m~v
For a pendulum: T = 2π
p
`/g
Newton’s Law of Gravity: F =
GM1 M2
r2
For uniform circular motion a = v 2 /r = ω 2 r
For a “balance beam” to balance it is necessary that:
The sum of the masses×distance to the fulcrum,
on one side of the fulcrum,
be equal to
the sum of the masses×distance to the fulcrum
on the other side of the fulcrum.
The “period” of a wave or oscillation is the time for one complete wave or oscillation.
Usually, the period is given the symbol T . For a pendulum,
p
T = 2π `/g
Also, frequency = 1/period
Doppler Effect:
fobs =
v
fsource , receding
(v + vsource )
fobs =
v
fsource , approaching
(v − vsource )
Beats:
(f1 + f2 )
= frequency heard
2
(f2 − f1 ) = beat frequency
1
Coulomb’s law:
F =k
q1 q 2
d2
where k = 9 × 109
Electric Field =
Electric Potential =
F
q
electric potential energy
electric charge
Electric potential is measured in volts, electric charge is measured in coulombs, and
energy is measured in joules (as usual).
“Potential difference” refers to the “difference” in the electric potential (usually measured
in volts) at two ends of a wire.
Ohm’s law:
Current =
voltage
resistance
Or, in units,
Amperes =
volts
ohms
Or, in symbols,
I=
V
R
Electric power:
Power = current × voltage
Or, in units
Watts = amperes × volts
Or, in symbols
Power = I × V
2