Lecture 23

Dead Cats & The Basics of Electricity

Bolemon Parts of Chapters 17-20

Probable First Observation of Electricity

Idiot?

If lightening had actually traveled down the kite string, old Ben Franklin would have been toast!

Don’t Mess With Mother NatureSt. Elmo’s Fire

Top of Mast

History

600 BC Thales of Miletos rubs amber (elektron

in Greek) and observed some strange effects.

Important questions: Why was he doing this? Didn’t he have a job?? What happened to the skinned cat?

AmberAmber

Million years ago large stands of forests in some parts of the world began to seep globs of sticky resin! This aromatic resin oozed down the sides of trees, as well as filling internal fissures, trapping debris, such as seeds, leaves, feathers and insects. As geologic time progressed the forests were buried and the resin hardened into a soft, warm, golden gem, known as amber. Amber is the fossilized resin of ancient trees which forms through a natural polymerization of the original organic compounds. Most of the world's amber is in the range of 30-90 million years old.

WARNING!WARNING!

These experiments do not always work! Humidity can hurt so do not exhale for the next 30 minutes!

Scotch tape

Required – 1 roll of tape 1 volunteer Observers

Demo Objects

Dead Cat – Skinned … keep the skin Rubber Rods Glass Rods Silk Cloth Wood Aluminum Metal 2 x 4 on a stand

45%3

24%

214%

157%

Rub 2 rubber rods with the skin of a dead cat

1. They will attract each other

2. They will repel each other

3. They will not interact with each other

4. It depends on when you killed the cat.

314%2

5%

181%

How does the Force of interaction depend on the distance?

1. It increases as the distance gets smaller between them.

2. It is independent of the distance.

3. It increases as the distance gets bigger.

333%

217%

150%

Rub 2 glass rods with silk

1. The rods will attract

2. The rods will repel3. The rods won’t do

anything.

410%

319%

257%

114%

Rubber rods with silk

1. Attract2. Repel3. Nothing4. They will

explode

310%

245%

145%

Rubber/Cat + glass/silk

1. Attract2. Repel3. Ignore each other

338%

219%

143%

Rubber and Cat’s Fur

1. Attract2. Repel3. No interaction

Some of the observations-RODS

Cat/Rubber Glass/Silk

Cat/Rubber Repel Attract

PLUS

The Glass attracted the silkThe Rubber attracted the dead

cat

Two Kinds of Interaction

AttractionRepulsion

Some conclusions (corrected) When two things are rubbed together,

something happens. We call what happens .. charging. It seems that there are two kinds of

charge The rubber charge is called NEGATIVE The cat charge is called POSITIVE

Like Charges Repel Un-Like charges Attract

30%

250%

150%

Based on our observations today, what charge winds up on the glass rod when rubbed by silk?

1. POSITIVE2. NEGATIVE3. Can’t Tell