ph102_overhead_ch12 - PCC

cypriotcamelUrban and Civil

Nov 29, 2013 (3 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)


They return to the original shape when the deforming
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)