Chapter 18 Solids

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

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

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)

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!

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

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

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

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

Problems for those who use this stuff Live, Dead loads Library (Purdue) Tacoma Narrows Bridge http://www.youtube.com/watch?v=j-zczJXSxnw Harmonic Resonance September 11th – live vs. dead load Urban Legend about college library Tacoma Narrow’s Bridge

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)