1. Chapter 18
Solids

2. This is Wicked Solid Stuff
Crystals
Structure not discovered until X-rays were available
Minerals and Metals have crystalline structures
Examples: quartz/salt

3. How Dense Can You Be
Density is a physical characteristic of all matter
Amount of Matter in a certain volume
NOT Dependent on total amount of matter you have
Stress ball example – loaf of bread example
Lead bullet vs. cannon ball – same density; swimming pool vs. glass of water

4. Calculating Density (D)ensity = (m)ass / (v)olume
units - kilogram/liter or gram/milliliter
Find the density of 95 kilogram Chris who has a volume of 81 liters.
Gold’s density is 19.3 grams/ml, what is the volume of a 1kg bar?
What is the mass of 2 liters of water
(density 1.0g/ml)?
1.17 kg/L;
51.8ml or 51.8 cm3 – square side 7.2 cm;
2000 grams or 2 kg (4.4 lbs)

5. Not Spastic, but… Elastic!
Elasticity is another physical property
Ability for something to return to its original position after being deformed
NOT STRETCHINESS!!!!!!
Inelastic – not elastic (can’t go back to original shape/position)
Rubberbands –sort of
Springs, steel – yes!

6. Let’s Spring into Action
Examples -
Springs, steel beams…
Non examples –
Clay, eggs …
Silly putty – stretchy, but not elastic – does not return

7. Look it’s Captain Hooke
Hooke’s Law F=kx
Elasticity of a spring is proportional to the applied force
Elasticity has its limits
Elastic materials cannot return to their original position when the elastic limit is reached
Elastic limit – beyond that it will not return – clothes; rubberband; slinky/spring

8. Using the Hooke (F)orce=spring konstant (k)*displacement(x)
A very tight steel spring has a spring constant of 35 N/cm. What force is required to stretch it 10 cm?
What is the spring constant if 15 N will stretch a spring 20 cm?
How far will 54 N bend a steel beam with a spring constant of 250. N/cm?
Do some hooke’s law examples 350 Newtons; .75N/cm; .216cm

9. Why Are You So Tense Compression (squeeze) Tension (stretch) I – Beams
Occurs when Atoms are being pushed together
Tension (stretch)
Occurs when Atoms are being pulled apart
I – Beams
Demonstrate with a piece of paper, weak, then fold it – stronger Straw into potato?
Some only 1 or other concrete, steel, paper – reinforced concrete
I – Beam look around the room and see how many you can see
NTQ after this slide

10. Problems for those who use this stuff
Live, Dead loads
Library (Purdue)
Tacoma Narrows Bridge
Harmonic Resonance
September 11th – live vs. dead load
Urban Legend about college library
Tacoma Narrow’s Bridge

11. Scaling, Scaling over the ocean blue
Find surface area and volume for cubes of side length 1,2,3 and 4 centimeters
As size increases, V grows faster than S.A.
Elephant ears, French fries, Falling bugs, cells
Have them do the cubes – complete chart on the board
Coal dust and explosions (ca-boom video from chem – flour bomb)
Starting a fire – what do you use (big chunk vs. shavings)