How’s the temperature in here?
• Fire is hot and snow is cold.
• But if you want to measure the
temperature in here, you need a
thermometer.
Hot vs. Cold
• Atoms are in constant motion.
• Atoms in the gas phase are zooming
around the room. (Translation)
• In the solid phase, the atoms can’t move
from place to place, but they can shake
back & forth. (Vibration)
• When something feels hot, the atoms
inside it are moving very fast.
link
Thermometers
• Galileo invented the 1st
thermometer in 1592. Didn’t
have a scale though.
Thermometers
• Liquid-in-glass thermometers – 1630’s
• No standard!
• Each scientist had his own scale
divisions.
• Couldn’t compare temperatures in
different places.
Thermometers
• Early 1700’s: developed standards
• Fahrenheit (1686-1736) invented alcohol
& mercury thermometers.
• Proposed 1st scale: 32F = freezing
point of water & 212F = boiling point of
water at 1 atm.
Thermometers
• Celsius (1701-1744)
• Proposed 0C = freezing point of water.
100C = boiling point of water.
Source: http://eo.ucar.edu/skymath/tmp2.html#Tmp
How do thermometers work?
• Molecules are in constant motion – they
have kinetic energy.
• Air molecules collide with the glass.
Kinetic energy is transferred to the
glass & then to the liquid through the
collisions.
• Molecules in liquid move faster and
spread apart.
• Length of liquid in column changes.
Absolute Zero
• Postulated by Kelvin in 1848.
• At absolute zero, the atoms are
stopped.
• Outer space is 3 above absolute zero.
• Absolute zero = 0K = -273.15C.
Lowest Temperature Ever
• 20 billionths of a degree above absolute
zero (0K)
• Press Release
Comparison of 3 Temperature Scales
source
Degree Size
• Kelvin & centigrade scales, 100
between freezing pt. & boiling pt. of
water.
• So degrees are the same size; scales
are offset.
• Fahrenheit scale has 180 between
freezing pt. & boiling pt. of water.
More degrees, so they must be smaller.
Conversions between scales
K = C + 273
Or
C = K – 273
Temperature Conversions
•
•
•
•
•
•
•
•
-150C 123K
-100C 173K
-45C 228K
0C 273K
38C 311K
85C 358K
115C 388K
200 473K
•
•
•
•
•
•
•
•
50K
100K
150K
200K
250K
300K
350K
400K
-223C
-173C
-123C
-73C
-23C
27C
77C
127C
Temperature vs. Heat
• Is temperature the same thing as heat?
• No. Temperature doesn’t depend on
how much matter you have, but heat
does.
• For example, does it cost more to heat a
swimming pool up to 40C or a teacup to
100C?
So what is temperature?
• Temperature is a measure of
the average kinetic energy of
the particles of a system.
What is Heat?
• The energy that flows from a
hot object to a cold object.
• Heat is a form of energy.