chapter 9 - thermal energy sections 9.1, 9.2, & 9.3
TRANSCRIPT
Chapter 9 - Thermal Energy
Sections 9.1, 9.2, & 9.3
ObjectivesBy the end of class today, you will be able to:
Define and describe thermal energy
Describe the relationship between temperature and kinetic energy
PS F-11, 15, 17
9.1 - Thermal Energy
All matter is made up of constantly moving atoms or molecules
The motion of a substance’s molecules determines if it is a solid, a liquid, or a gas
When molecules are made to move faster, they gain kinetic energy.
9.1 - Thermal Energy
In general, the warmer an object is, the more kinetic energy its atoms and molecules possess.
We can also say that the warmer an object gets, the more thermal energy it contains.
9.1 - Thermal Energy
What is thermal energy?
The total energy of all an object’s atoms and molecules
Thermal energy consists of both the potential and kinetic energy of the particles in a substance as they move around.
9.2 - Temperature
Why do we measure an object’s temperature?
To be able to tell how warm or cold it is.
A thermometer measures by expansion or contraction of a liquid, usually colored alcohol.
9.2 - Temperature
Temperature Scales -
Celsius Scale - O° is the freezing point of H₂O and 100° is the boiling point of H₂O.
Fahrenheit Scale - 32° is the freezing point of H₂O and 212° is the boiling point of H₂O.
9.2 - TemperatureTemperature is related to the random motion of atoms/molecules in a substance.
Temperature is related to the average KE of molecular motion.
A substance with a high temperature has molecules with high average KE
The molecules are moving very fast if the object has a high temperature
Which box has a larger temperature?
9.2 - TemperatureConcept Check Question:
True or False -
Cold is the absence of moving molecules.
False!
Cold refers to very-slow moving molecules, not their absence. Without molecules, the concept of temperature is meaningless!!!
9.3 - Absolute Zero
In principle, there is no upper limit to temperature.
As thermal energy keeps increasing, a solid object melts to a liquid and then evaporates into a gas.
9.3 - Absolute Zero
However, there is a definite limit at the lower end of the temperature scale.
This limit is called absolute zero!
9.3 - Absolute ZeroIn degrees Celsius, this temperature is -273°!
At this temperature, molecules have lost all available KE.
No more energy can be taken from a substance at absolute zero.
It can’t get any colder!!!!
9.3 - Absolute Zero
The absolute temperature scale is called the Kelvin scale.
Absolute zero is 0 K. (Kelvin)
There are no negative numbers on the Kelvin scale.