# Chapter 15 TEMPERATURE, HEAT, AND EXPANSION Temperature

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"Chapter 15 TEMPERATURE, HEAT, AND EXPANSION Temperature"

```					 Chapter 15 TEMPERATURE,
HEAT, AND EXPANSION

• Temperature is a measure of the
average translational kinetic energy of
molecules
• Tells how warm or cold object is with
respect to some standard.
• Tells us which way heat will flow (from
hot to cold)

Galloway-PHYS 1310 Chapter 15

Elaboration

Temperature

What’s the difference
between a beaker of
cold water and a
beaker of hot water?                            cold   hot

Galloway-PHYS 1310 Chapter 15

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TEMPERATURE SCALES

• FAHRENHEIT (32 – 212 oF)
• CELSIUS (0 – 100 oC)
• KELVIN (Absolute with Celsius sized
increments) (273 K -373 K)
• 00 Celsius = 273 Kelvin

Galloway-PHYS 1310 Chapter 15

HEAT

• The energy transferred from one object
to another due to temp difference.
• CALORIE (a unit of energy)
• 1 CALORIE = Amount of heat needed to
raise 1 gram of water by 1 degree
Celsius.

Galloway-PHYS 1310 Chapter 15

2
Engage

Mixing Water

If you mix some cold water and some hot
water, what’s the final temperature? Can
you predict what it would be?
Suppose you put the same amount of
heat into 1 liter of water as you put into 2
liters of water?

Galloway-PHYS 1310 Chapter 15

Explanation

Heat Transfer
As the hot water cools down, the
cool water warms up..

Heat gained = Heat lost

As an example, if 20 calories of
heat are lost by 5 g of water, then
each gram of water loses 4 calories
and the temperature of the 5 g of
water will decrease 4°C in
temperature.Galloway-PHYS 1310 Chapter 15

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Elaborate

Heat Transfer Examples
Suppose you have 5 g of water at 20°C and you add 10
cal of heat, what is the final temperature? What if you

There would be 10 cal for 5 g of water or 2 cal for each g.
The water would heat up 2 °C and the final temp would
be 22°C.

Suppose you have 10 g of water and you want to raise the
temperature by 7°C. How much heat must be added?

You would need to add 7 cal for each g of water. Since
there are 10 g, this would mean adding 70 calories.

Galloway-PHYS 1310 Chapter 15

SPECIFIC HEAT CAPACITY

• Heat required to raise the temp of 1 gm
substance by 1 degree Celsius.
Heat = (mass) x (temp change) x (specific heat)
Heat lost = Heat gained
Heat is a form of energy

Energy is conserved.

Galloway-PHYS 1310 Chapter 15

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Explanation

Specific Heat
Specific Heats
aluminum = 0.22 cal/ g·°C
copper = 0.09 cal/g·°C
glass = 0.20 cal/g·°C
water = 1.0 cal/g·°C
ice = 0.53 cal/g·°C
vegetables = 0.9 cal/g·°C
fat = 0.5 cal/g·°C

Different substances have
different specific heats?
What are some of the
effects of this observed in
everyday life?

Galloway-PHYS 1310 Chapter 15

Explanation

Heat transfer in substance
Heat = mass x temp change x specific heat
Suppose you add 20 cal to 10 g of Aluminum, what is the
temperature change?

20 cal = 10 g x (temp change) x 0.22 cal/g·°C
Temp change = 20 cal/(10 g x 0.22 cal/g·°C)
Temp change = 9.1°C

Suppose you add 20 cal to 10 g of water, what is the
temperature change?

20 cal = 10 g x (temp change) x 1 cal/g·°C
Temp change = 20 cal/(10 g x 1 cal/g·°C)
Temp change = 2°C
Galloway-PHYS 1310 Chapter 15

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Examples of heat capacity
Q. Which will stay cooler after you
take them out of the refrigerator on
a hot day… a watermelon or a
sandwich?

A. The watermelon will because it has
much more water than the sandwich and
water has a greater specific heat than the
non-watery parts of the sandwich.

Physics, Florida Atlantic University
Galloway-PHYS 1310 Chapter 15

Engagement

Examples of heat capacity
Q. In the ‘good ol’ days’ on a cold
night it was common to take a hot
object to be with you(!). Would
you be better to keep warm
through the night with a 10 kg
iron brick or a 10 kg container of
water?
A. The brick would lose heat more
rapidly than the water because iron has
a much smaller specific heat than water.
As a result, the heat given off is much
less than the same mass of water.
Physics, Florida Atlantic University
Galloway-PHYS 1310 Chapter 15

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THERMAL EXPANSION

• Most materials expand
when heated.
• Different materials expand
at different rates.
• Road joints on bridges are
from buckling.
• Demo with bimetallic strip

Galloway-PHYS 1310 Chapter 15

STRANGE CASE OF WATER

• WATER IS MOST DENSE AT 4O C.
VE 14-9(Thermostat Model), 10(Pin Breaker), 13(Thermal Expansion of Water), 14(Negative
Expansion Coefficient of Water)

Picture from Hewitt, Conceptual Physics, p. 300

Galloway-PHYS 1310 Chapter 15

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Heat and Energy
Heat is a form of energy. Discuss
where the energy given off by the
light in a light bulb arises. Can you
trace this energy back to its
source?

Galloway-PHYS 1310 Chapter 15

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