12 Overview

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# 12 Overview - PowerPoint PPT Presentation

12 Overview density elasticity & Hooke’s Law Homework: RQs: 8, 9, 10, 11. Density Density = mass/volume depends on chemical type and structure water 1.0 grams/cm 3 ice 0.9 grams/cm 3 copper 8.9 grams/cm 3 lead 11.9 grams/cm 3 Density Units 1.0 grams/cm 3 = 1,000 kg/m 3

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## 12 Overview

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Presentation Transcript
12 Overview
• density
• elasticity & Hooke’s Law
• Homework:
• RQs: 8, 9, 10, 11.
Density
• Density = mass/volume
• depends on chemical type and structure
• water 1.0 grams/cm3
• ice 0.9 grams/cm3
• copper 8.9 grams/cm3
Density Units
• 1.0 grams/cm3 = 1,000 kg/m3
• think of 264 gallons of water, each gallon weighs 8.35 lbs.
Elasticity - ability to regain shape
• elastic material – perfectly regains shape
• inelastic material – incompletely regains shape
• elastic limit – force in which an elastic material becomes inelastic
Hooke’s Law
• Elastic Force ~ amount of stretch or compression
• F ~ Dx; F/Dx = spring constant (stiffness)
• Example: many springs obey Hooke’s Law within their elastic limit.
Summary
• density is mass/volume, 1.0 grams/cm3 = 1,000 kg/m3
• Hooke’s Law: deformation ~ force
Crystal Structure

solids with a regularly repeating pattern are crystals

Examples: Graphite NaCl

hexagonal

cubic

X-Ray Crystallography

X-Rays are used to determine the structure of crystalline solids

raindrops
• which falls faster, small or large raindrops?
• 5 mm drops: ~9 m/s (20 mph)
• 0.5 mm: ~2 m/s (4 mph)
• why?
• A. Scaling
Scaling
• mass & weight increase at L3 , but area & strength increase with L2.
• raindrops: weight increases faster than air-drag as size increases, causing terminal velocity to increase.