planning for changes: examples of expansion and contraction
TRANSCRIPT
Planning for changes:
Examples of expansion and contraction
Expansion and Contraction
• When things heat up:– 1-The atoms speed up– 2- The atoms move
further apart from each other
– 3- The object expands (gets bigger)
– 4- Diffusion happens faster.
Example
• Have you ever shattered a glass bowl in the microwave, or pulled a hot glass out of the dishwasher and put cold water in it, and it cracked or broke?– Glass doesn’t transfer
heat very well, so it expands unevenly.
Example
• How does this concept help you understand how a thermometer works?
Manmade structures
• We have to consider the expansion and contraction of solids when we build things.
• (The Eiffel tower is 6.75 inches shorter in winter than in summer!)
Expansion joints in steel bridges
• Bridge builders include expansion joints in their bridges so that the bridges won’t break as the weather changes
Steel bridges
Railroad tracks
• Railroad tracks have gaps at each joint so that the rails can expand and contract without snapping.
Railroad tracks
Concrete Roads
• Concrete roads have expansion joints built in so that they don’t crack when the sun heats up the tar in the road.
Sidewalks• Sidewalks have
“seams” every so often to allow the sidewalk to expand and contract.
Car parts• Car engine parts
are designed to be a little loose when the car is cold so that they will not break when the engine warms up.
Water: The rule breaker
• Water is the only liquid that expands (gets bigger) when it freezes.
• How might this cause cracks in the road or sidewalk to get worse over time?
Water: The rule breaker
• Water forms hydrogen bonds when it freezes, which causes it to expand.
• Water is actually most dense at 4 degrees celcius.
Quiz time!
• Jim had trouble getting the lid off a jar of jam. He ran the lid under hot water for a minute, and it came right off. Why does this work?
Quiz time!
• What happens to a marshmallow as your roast it?– Why?
Quiz time!
• Your mom complains that her ring fits too tightly sometimes, but at other times it falls off.– What might be a
possible explanation for this?
Quiz time!
• True or false:– Atoms and molecules are always moving.
Quiz time!
• What happens to molecules when they heat up?– A- They move faster– B- They move more slowly– C- They get further apart– D- They get closer together