Category: physics

Abus = 0.8 m/s^2
Vmax = 20m / s

Abike = 1.2m/s^2
Vmax = 12m/s

Air Pressure = Weight / Area
P = F / A

-Unintuitive
-Very Fast

C = 3 * 10^8 m/s
299,792,458 m/s

Where to Begin?
Einstein, Galileo

Two postulates, logic, conclusion

Spaceship Flyby2
t’ = γt
γ= 1/√1-β^2

orbit satellite
β = 14000km / hr * 1000m / Km * 1hr / 3600s = 3890 m/s

Wret = ΔPE
= PEf – PEo

Dead Reckoning
Direction, speed, duration
East, 12km/h, 2.5hrs
south, 20km/h, 1hr

The total charge in the universe never changes.
Closed System -> No charge being added to or removed from the system.

Friction
Conduction
Induction

Infinite source and sink of electrons
Grounding

Electric Potential Energy
When r is small, Ue is highest.
Ue = K q1q2/r
K = 9*10^9

E = 1000 N/C
d = 1cm
Mp = 1.673 * 10 ^ -27
g = 1.602 * 10 ^ -19C

F = Eg
na = Eg
a = Eg/m

ΔKE = Egx
W = Fx = Egx

Electricity
Leyden Jar -> charged

Ben’s contribution
charge +-, conservation of charge

CHARGE is a property of matter
Why is mass so important?

Fe Fg
cause: Q:m
effect: Q:m
Force Law: Fα1/^2:Fα1/r^2
Direction of force

Attraction / Repulsion
– Opposite charges attract
– Like charges repel

Coulomb
Electricity is really strong

proton
1.6 = 10^-19C
neutron = 0
electron
-1.6 * 10^-19C

X(t) = XmaxSin(ωt + π/2)

Adjusting the Period
Fs = -Kx
F = ma
ma = -Kx, a = -k/m * x

K = 50 n/m
T = 1sec
m = 1.27Kg

The simple pendulum
SHM: a = -?x
F = ma
-mg*sinΘ = ma

Gmean = 1.6m/s^2
ge = 9.8 m/s^2
Te = Tm
Lm = lm/le Le
= 1.6/9.8 Le

1) Latitude
2) Longitude

Latitude is easy to exactly find out.
Calculating latitude, tropic of cancer and equator
α is exact same degree of sun shadow

Longitude is completely arbitrary

How to keep the time?
-Need Periodicity

We need chronometer
-periodic, isochronous, predictable

Equilibrium
c = 2πr
2πradians = 360°

cos(3π/4)=-0.707
Sin(3π/4)=0.707

Angular Velocity w
ΔΘ=ωt

KE = 1/2 mv^2

mgh vs -Gmem/r
Gravitational Potential Enery
G = 6.674 * 10^-11Nm^2/kg^2
re = 6400km, Me = 5.97*10^24kg

KE0 + U0 = KEf + Uf

All objects are mutually attracted
– Accelerate at 10m/s^2

The Train… of Pysics!
What trajectory would the apple follow?

In physics motion at constant speed is indistinguishable from being at rest!

F:10N
time:4.47sec
acceleration:1 m/s^2

Δx=v0t+1/2at^2
10m = 0 + 1/2a(4.47)^2

N = Normal(perpendicular)
FN mg=weight, mg is equal to FN

Forces and trig
if α=30°、Fr=100N sin(30degree)*100
FRX = 50N, Fry = 86.6N cos(30degree)*100

m = 10Kg
mg = 100N
Fry = 50N
Fn = 150N
Frx = 86.6N
Fw = 86.6N

2-D motion can be solved as two
1-D motion problems

Δx = V0t + 1/2αt^2
V = V0 + at
V^2 = V0^2 + 2αΔx

Δox = 10m/s
α- 10m/s^2

Dimensional Analysis
E = mc^2, E = M*L*T

Experiment, Evidence Rules, Motion Equation
1D/ 2D ΔX = v0t + 1/2at^2

Explain the cause of motion
Understand “rest”

the motions of stars and apples have in different, but governed by same laws

Kinematics
1. predictive power
2. important tool
3. solve nature’s puzzle

Galileo Galilei:object fall at constant speed
Aristotle vs Galileo: objects gain speed as they fall

A mass dropped from greater height leaves greater impact
Feathers do fall at constant speed
Air slows objects down! … too fast

Position, Velocity
Velocity: v = Δx / Δt
Acceleration a = ΔV / Δt

v = 5m / 1s = 5 m/s

Average deviation
2.00m, 1.20m, 2.80m -> 1.6/3 => 0.53
1.97m, 1.98m, 1.97m -> 0.02/3 => 0.0067
m / s / s
“constant acceleration means an object gains equal speed during equal time intervals”
Vαt^2
x = t^2, a = 10m/s^2 = g
V0 = 10m/s