Temperature and Thermal Energy:

Part 1Physics

In this lesson, we will discuss the

following:

Temperature

Absolute Zero

Thermal Energy

Classroom Ambush: Define Temperature

Temperature

On the macroscopic scale, temperature is a measure of how warm a substance is.

If something is macroscopic, it can be seen with the naked eye.

Temperature

• Molecules and atoms can move in three different ways. The three kinds of particle motion are as follows:– Translational motion is motion in straight lines.– Rotational motion is the motion of a particle as it

rotates on its own axis.– Vibrational motion is the shaking or vibrating of

atoms or molecules.

Temperature1Translational

motion is motion in

straight lines.

Temperature1Rotational motion is the rotation of a

particle about its own axis.

Temperature1Vibrational motion is the

shaking or vibrating of

molecules or atoms.

Temperature

On the microscopic and submicroscopic scales, temperature is defined as the average translational kinetic energy per particle (atom or molecule) of a substance.

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Temperature

In other words, temperature is basically a measure of how fast molecules or atoms are moving in straight lines.

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Temperature

• Temperature is a “per particle” property. In other words, you can measure the temperature of an individual atom or molecule.

• In addition, for constant conditions, the temperature of a substance is independent of number of molecules or atoms. A substance can have a very high temperature even if it is made of very few molecules.

Abbreviation for Temperature

We will abbreviate temperature as T.

T

Temperature Scales

• The two temperature scales we will see in our class are the Celsius scale and the Kelvin scale.– The Celsius scale has 00 Celsius at the freezing point of

fresh water and has 1000 Celsius at the boiling point of fresh water. The Celsius scale is sometimes called the Centigrade scale.

– The Kelvin scale has 0 Kelvin (not degrees in Kelvin scale) at absolute zero, and for this reason, the Kelvin scale has no negative temperatures. The Kelvin scale is also called the Absolute scale. On the Kelvin scale, the freezing point of fresh water is 273 K, and the boiling point of fresh water is 373 K.

Temperature Scales

When in doubt, use the Kelvin scale!

SI Unit for Temperature

The proper SI Unit for Temperature is the Kelvin (K). DO NOT USE the word “degrees” when expressing temperature in Kelvin.

Temperature is a Scalar Quantity

Temperature is a scalar quantity. In other words, temperature has no direction.

Absolute Zero

• Temperature has NO upper limit. In other words, temperature can theoretically increase infinitely.

• However, temperature DOES have a lower limit. This lower limit is called absolute zero.

• In fact, temperature can never quite actually reach absolute zero, it can just approach it.

Absolute Zero• When a substance has reached absolute zero, all of its particles (molecules and atoms) have lost all available energy.

• A substance can never get any colder than absolute zero. In fact, a substance can’t quite get to absolute zero.

Absolute Zero• On the

Fahrenheit scale, absolute zero is −459.670 F.

• On the Celsius scale, absolute zero is -2730 C.

• On the Kelvin scale, absolute zero is 0 K.

Thermal Energy

• Thermal energy is defined as the total energy of all of the particles that make up a substance.

• The more particles a substance has, the higher its thermal energy.

Why Doesn’t a Sparkler Burn You?

• A sparkler emits sparks which are very hot (about 20000 C).

• But, a sparkler only emits a few sparks.• Because only a few sparks are emitted by a

sparkler, the thermal energy that a sparkler can transmit to your hand is quite small.

• Your hand does not get burned because very little thermal energy is transferred from the sparks to your hand.

Abbreviation for Thermal Energy

We will abbreviate thermal energy as .thE

Acceptable Units for Thermal Energy

• The SI unit for all energy is the Joule, but the calorie, and the Calorie are also acceptable units.

Calorie calories J1 000 , 1 180 , 4

A Calorie is

also ca

lled a

kilocalorie. T

his is th

e same

thing as a fo

od calorie

.

Thermal Energy is a Scalar Quantity

Thermal energy is a scalar quantity (like all other forms of energy). Thermal energy has no direction.