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.

HotHot vs. ColdCold

• 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: 32F = freezing point of water & 212F = boiling point of water at 1 atm.

Thermometers

• Celsius (1701-1744)

• Proposed 0C = freezing point of water. 100C = 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. Air molecules collide with the glass. Kinetic energy is transferred to the Kinetic energy is transferred to the glass & then to the liquid through the glass & then to the liquid through the collisions.collisions.

• Molecules in liquid move faster and spread apart.

• Length of liquid in column changes.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 = -273.15C.

Lowest Temperature Ever

• 20 billionths of a degree above absolute zero (0K)

• Press Release

Comparison of 3 Temperature ScalesComparison 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 = K = C + 273C + 273

Or Or

C = K – 273C = K – 273

Temperature Conversions

• -150C• -100C• -45C• 0C• 38C• 85C• 115C• 200

• 50K• 100K• 150K• 200K• 250K• 300K• 350K• 400K

123K173K228K

273K

311K358K388K473K

-223C-173C

-123C-73C-23C27C77C127C

Temperature vs. Heat

• Is temperature the same thing as heat?

• No. Temperature doesn’t depend on No. Temperature doesn’t depend on how much matter you have, but heat how much matter you have, but heat does.does.

• For example, does it cost more to heat a swimming pool up to 40C or a teacup to 100C?

So what is temperature?

•Temperature is a measure Temperature is a measure of the average kinetic of the average kinetic energy of the particles of a energy of the particles of a system.system.

What is Heat?

•The energy that flows from The energy that flows from a hot object to a cold a hot object to a cold object.object.

•Heat is a form of energy.Heat is a form of energy.