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Nov 29, 2013 (4 years and 7 months ago)

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Phy 102: Fundamentals of
Physics II

Chapter 12 Lecture Notes

English chemist, mathematician,

physicist, and inventor
(the spiral spring)

England’s 1
st

experimental scientist.

Founder of many scientific fields, including:

Microscopy

-

Microbiology

Meteorology

-

geology

Earth sciences

Robert Hooke
(1635
-
1702)

Gained acclaim for writing the 1
st

microscopy textbook

Known for his creating brilliant ideas but not following
them up to develop complete theories

Contemporary
(& scientific enemy!)

of Isaac Newton

Hooke claimed Newton “stole” many of his ideas including his
theory of universal gravitation and a particle theory of optics

Hooke was known for his frequent and bitter disputes with
fellow scientists

Solids

Substance with definite shape & definite volume

Classifications of solids

Crystalline (regular)

Amorphous (irregular)

Types of solids

Ionic

Covalent

Metallic

Van der Waals

Density

A physical property of matter

The relationship between a substance’s mass and
the volume of space it occupies

Depends on

Mass of the atoms/molecules

How tightly the atoms are packed together

To calculate density:

Density = mass/volume

or

D = m/V

Units are

SI: kg/m
3

Other: g/cm
3

(or g/mL), kg/L, g/L

Elasticity

Elastic materials have 2 characteristics:

They change shape when a deforming force acts on an
object
(e.g. compress or stretch)

force is removed

The force (F) required to deform an elastic material
is proportional to the amount of deformation the
object experiences (
D
x):

F ~
D
x

{This is called
Hooke’s Law
}

Elastic materials can be stretched/compressed past
a point
(called the
elastic limit
)

beyond which Hooke’s
Law no longer applies
(& they stay permanently deformed)

The Soloflex

Tension & Compression

Something pulled on (stretched) is referred to as being
under tension

Something pushed in is
in compression

When something is bent:

the outside part of it is in tension

the inner part is in compression

Somewhere between these regions is an interface called
the
neutral layer

(where neither tension nor compression occurs)

Steel girders are designed in “I” shapes to that
maximum material is at tension/compression regions &
minimal material is located at the neutral layer
(to
maximize stretch & minimize weight)

Arches

An inexpensive restaurant specializing

in fried foods

Scaling

An object’s strength is proportional to its cross
-
sectional
area (A):

Strength ~ A
(measured in m
2

or cm
2
)

An object’s mass is proportional to its volume (V):

Weight ~ V
(in m
3
or cm
3
)

As objects increase in size, volume & weight increase
faster than cross
-
sectional area & strength

This results in disproportionately larger support features (such
as legs)

Lighter animals tend to have thin legs (spiders, deer, etc.)

Heavier animals tend to have thick legs (rhinos, elephants,
hippos)