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

{ }

Physics OlympicsPenny Barge

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!!!!

Bed of Nails

Ratios: P=F/A

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

Inertia

Average FreightTrain 55 mph= 1 mile

Up to 3300 lbs

Stay at Rest

Stay in Motion

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