Conceptual Physics Heat 1c: Thermal Expansion

Thermal Expansion Most forms of matter expand when heated and contract when cooled. Consider BRIDGES…RAILROAD TIES…SIDEWALKS!

Demo #4 What will happen if these two metals are bonded and then heated?

Thermal Expansion

Thermostat – Application of a bimetalic strip

Thermal Expansion As most forms of matter expand when heated and contract when cooled how does this affect: Jar tops? Potholes? ( ice wedging ) – Why is water weird? hyperphysics.phy-astr.gsu.edu

Thermal Expansion Due to the “weird” angular shape of the water molecule the solid form (right) of water is greater in volume than the liquid form (left). lbl.gov

Thermal Expansion What happens to the volume of water as it warms from 0˚C to 4˚C? Where would you find 4˚ C water in a lake?

Thermal Expansion A given amount of water has its smallest volume (greatest density) at 4˚C. Same amount of water has its largest volume (smallest density) in its solid form… ice… at 0˚C. – Thus ice floats! mrbarlow.wordpress.com jisibhlphysics.wikispaces.com

Thermal Expansion As temperature increases the ice crystals collapse thus their volume decreases. lbl.gov

Thermal Expansion As temperature increases the ice crystals collapse thus their volume decreases. As temperature continues to increase, molecular motion increases and volume increases. lbl.gov

Thermal Expansion As temperature increases the ice crystals collapse thus their volume decreases. As temperature continues to increase, molecular motion increases and volume increases. lbl.gov

Thermal Expansion As temperature increases the ice crystals collapse thus decreasing their volume. As temperature continues to increase molecular motion increases and volume increases. The combined effect results in the “look” of the temp- volume curve: lbl.gov

Thermal Expansion Water is more dense at 4˚C so it sinks. Water at 0˚C is less dense so it floats. As outside air temp drops to “below zero” water cools becoming more dense and sinks. Once all water is cooled to 4˚C the water exposed to the “below zero” air above begins to cool further becoming less dense. Ice forms and then floats on the water surface. Water on the underside of ice sheet then begins to cool further forming ice and adding to the ice sheet from below. VERY COOL … HUH?? benabb.wordpress.com

Thermal Expansion What would happen if lakes froze from the bottom up? pixdaus.com

Thermal Expansion In the fall, what happens to water as it cools? What would happen if lakes froze from the bottom up? lake mixing