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Thermal Expansion

Thermal Expansion. Schaums chapter 15. Why does a solid expand as it is heated. The bonds between molecules act like tiny springs that start to vibrate faster as thermal energy ( heat) is added to them. This causes the material to expand as the molecules push and shove against each other.

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Thermal Expansion

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  1. Thermal Expansion Schaums chapter 15

  2. Why does a solid expand as it is heated • The bonds between molecules act like tiny springs that start to vibrate faster as thermal energy ( heat) is added to them. This causes the material to expand as the molecules push and shove against each other

  3. The linear expansion of a solid (change in length) as it is heated is nearly linearly proportional to the change in temperature. This means for example that if you increased the temperature of a metal rod by 50° and its length increased by 1 mm, then if you increased its temperature instead by 100° its change in length would be 2 mm

  4. The change in the length,area, and volume as a function of temperature is critical in engineering and design. • One example is the change in the pistons in the engine of your car as the engine heats up. If the pistons just fit into their sleeves when the the car is started up, then as the car warmed up the pistons would “seize” inside the piston sleeves. Thus the engineer must compromise by making the pistons smaller than the sleeves they fit into. This is one of the reasons a car’s performance improves as it warms up

  5. The coefficient of area expansion and volume expansion • Linear expansion

  6. Example 1 • A copper bar is 80 cm long at 15°C. What is the increase of length when it is heated to 35°? The linear expansion coefficient for copper is 1.7 x 10^-5 C^-1

  7. When in doubt always use SI units (meters instead of cm) in your calculations and final answers. Fortunately, with little exception, The AP and IB will give you free response problems where all the input numbers are given in proper SI units. The homework in Schaums deliberately gives both in order to increase the practice you get in conversions and recognition of SI units

  8. Example 2

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