### Heat, Temp, Thermal Expansion

```*
* Measured in K, ºC, ºF
* Lower limit … 0 K
* Upper limit … none
* K and ºC have the same scale, just offset
* Practice converting to all three scales:
* 50ºF
* 10ºC
* 550 K
*
* No!!
* Heat … measured in J, a form of ENERGY
* Temperature is a measure of the AVERAGE
kinetic energy of ALL the molecules in the
substance.
* More motion (vibrations) = more KE
* More KE = higher Temp.
* Rationalize why this makes sense…
*
* The sum of all of the molecules’ KE
* Even if it is colder, if there is more of that
substance, then it will have a greater Thermal
Energy
* Ex.
Hot chocolate vs. the Atlantic in winter
*
* There is twice as much molecular kinetic energy in 2
liters of boiling water as in 1 liter of boiling water.
Which will be the same for both?
* A.
* B.
* C.
* D.
Temperature
Thermal Energy
Both A and B.
Neither A nor B.
A. Avg. KE of molecules is the same.
*
* To say that body A has a higher temperature than
body B is to say that body A has more
* A.
* B.
* C.
* D.
Internal Energy.
Mass.
KE per particle.
PE
C
*
* Internal energy transferred due to unequal
temperatures
* Heat flows until thermal equilibrium is reached
* What is that?
* ALWAYS flows from hot to cold.
* An object does NOT contain heat.
*
* If a red-hot thumbtack is immersed in warm
water, the direction of heat flow will be from
the:
* A.
* B.
* C.
* D.
Warm water to the red-hot thumbtack
Red-hot thumbtack to the warm water
There will be no heat flow
Not enough information
B
*
* Heat is ENERGY
* Joules
* 4.186 J = 1 cal
* Food calories are NOT the same.
* 1 food calorie = 1 kilocalorie (kcal) = 1000 cal
*
* The same quantity of heat is added to different
amounts of water in two equal-size containers.
The temperature of the smaller amount of
water…
* A. Decrease more.
* B. Increases more.
* C. Does not change.
* D. Not enough information
*
* You heat a half-cup of tea and its temperature
rises by 4ºC. How much will the temperature
rise if you add the same amount of heat to a
full cup of tea?
* A.
* B.
* C.
* D.
0ºC
2ºC
4ºC
8ºC
2ºC
*
* As substances are heated…
* Motion increases
* KE increases
* Molecules move faster and further apart
* Substance expands!
* Opposite when cooled.
* Different substances expand at different rates
* Greater in liquids than in solids
* More liberty to move
* Important for construction!!
*
• Use of reinforcing steel with the same
rate of expansion as concrete—
expansion joints on bridges.
• Gaps on concrete roadways and
sidewalks allow for concrete expansion in
the summer and contraction in the winter.
*
Rail Buckling
* When stringing telephone lines between poles in the
summer, it is advisable to allow the lines to…
* A.
* B.
* C.
* D.
Sag
Be taut
Be close to the ground.
Allow ample space for birds.
A…Telephone lines are longer in a warmer
summer and shorter in a cold winter. Hence, they sag
more on hot summer days than in winter. If the lines
are not strung with enough sag in summer, they might
contract too much and snap during the winter—
especially when carrying ice.
*
* Water molecules form a crystalline structure
when they become a solid.
* Each water molecule takes up more space than
when it was a liquid because of the bonds it
makes in its crystalline structure
*
*As water molecules get colder, they take up less
space (cold things contract), until ~4C (39F). This
is the maximum density of water
*Below 4C, water begins to form its crystal
structure as it approaches its freezing point,
decreasing density
*As water gets warmer, molecules expand,decreasing
density
*Important for ocean circulation, heating of Earth,
and overturning of fresh bodies of water
*
* When a sample of 0C water is heated, it first
* A. Expands
* B. Contracts
* C. Remains unchanged
* D. Not enough information
B. Water continues to contract until it
reaches a temperature of 4C. With further increase
in temperature beyond 4C, water then expands.
*
* When a sample of 4ºC water is cooled, it…
* A.
* B.
* C.
* D.
Expands
Contracts
Remains unchanged
Not enough information