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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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Presentation Transcript

• density

• elasticity & Hooke’s Law

• Homework:

• RQs: 8, 9, 10, 11.

• Density = mass/volume

• depends on chemical type and structure

• water 1.0 grams/cm3

• ice 0.9 grams/cm3

• copper 8.9 grams/cm3

• 1.0 grams/cm3 = 1,000 kg/m3

• think of 264 gallons of water, each gallon weighs 8.35 lbs.

• elastic material – perfectly regains shape

• inelastic material – incompletely regains shape

• elastic limit – force in which an elastic material becomes inelastic

• 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.

Longer objects are easier to stretch. Thicker objects are harder to stretch.

• density is mass/volume, 1.0 grams/cm3 = 1,000 kg/m3

• Hooke’s Law: deformation ~ force

solids with a regularly repeating pattern are crystals

Examples: Graphite NaCl

hexagonal

cubic

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

• 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

• 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.