Physics is Phun David S. Wright Professor of Physics Tidewater Community College.
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Physics is Phun David S. Wright Professor of Physics Tidewater Community College
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Transcript of Physics is Phun David S. Wright Professor of Physics Tidewater Community College.
Physics is PhunDavid S. Wright
Professor of Physics
Tidewater Community College
7 in 1 Survival ToolWhistle
Compass
LED Light
Magnifying Glass
Mirror
Thermometer
Empty Space
Inverse Proportion ToolWhistle
Compass
LED Light
Magnifying Glass
Mirror
Thermometer
Empty Space
Whistle
Intensity= k/r2
Whistle
f=k/
LED Light
I=k/r2
Magnifying Glass
Totally Inverse 1/f= 1/do + 1/di
Thermometer
Coiled Bimetal Strip Liquid in Glass
Bimetal Thermometer
Radius=k/T
Mirror
Gives an Inverse of the Image
Without MirrorWith Mirror
Compass
Magnetic Field (B) of an ideal dipole, measured along its axis?
B=k/r3
Empty Space
{ }
Basket ball and Tennis ball
1 meter
mBvB1+mTvT1=mBvB2+mTvT2
Conservation of Momentum
Conservation of Energy
½ mBvB12 + ½ mTvT1
2 =
½ mBvB22+ ½ mTvT2
2
vB1=+4.5 m/s vB1= 0 m/s
vT1 = -4.5 m/s vT1= -9.0 m/s
mTvT1=mBvB2+mTvT2
mTvT12 = mBvB2
2+ mTvT22
This “simplifes” the equations:
Now it’s great fun to solve these!!!
vB2=(mTvT1-mTvT2)/mB
mTvT1=mBvB2+mTvT2becomes
Then
mTvT12 =mB ( )2+mTvT2
2(mTvT1-mTvT2)/mB
Then some factoring and hand waving occurs…
Eventually
vT2=(mT-mB)(mT+mB)
vT1
mB=.4 kg mT=.07 kg vT2= 6.3 m/s
Vfinal with respect to floor= 10.8 m/s
Final Height=5.8 m!!!!
Pressure Elephant’s Foot: 6000 lb Elephant Foot ~ 40 in2
P=F/A=6000 lb/40in2 = 150 psi
Pressure Woman’s Stiletto Heel: 100 lb woman Spike Heel~ 1/16 in2
P=F/A=100 lb/(1/16 in2) = 1600 psi
Bed of Nails
160 lb Professor/320 nails
That’s only ½ lb per nail!
InertiaSylvester's law of inertia
The number of eigenvalues that are postive, negative or zero do not change under a
congruence transformation. When a quadratic Q in n variables is reduced by a nonsingular linear transformation to the
form Q=y1
2+y22+…+yP
2-yP+12-yP+2
2-…yn2 the number P of positive squares appearing inthe reduction is an invariant of the quadratic
form Q and does not depend on the method of reduction.
Inertia
Average FreightTrain 55 mph= 1 mile
Up to 3300 lbs
Stay at Rest
Penny Barge
10 cm
x10cmx
10-2x
x
10-2x
Maximize Volume
V= L * W* H
L=10-2x W=10-2x H=x
V(x)=x(10-2x)2=4x(x2-10x+25)
dV/dx=0=4(x2-10x+25)+4x(2x-10)
dV/dx=4(3x2-20x+25)=0
Penny Barge
Solving by the Quadratic Formula x=5 x=5/3
6 2/3 cm
6 2/3 cm
5/3 cm
Leaf Blower
The Leaf blower and toliet paper involves Bernoulli’s Principle, Inertia, Force, Acceleration, but most of all it proves that…
Physics is Phun
