1. Part 1: Weather, Lesson 5 Absolute Zero
What is the coldest temperature you have ever experienced?
What is the coldest temperature ever recorded in the USA?
-79.8°F or -80*F You can Google it!!
Researchers have recorded temperatures of -235°C on the surface of Triton, a moon of Neptune.

2. Weather, Lesson 5 Absolute Zero
How cold can it get?
To answer this question we will explore
Absolute zero
Kelvin Scale
Molecules in Motion
Absolute Zero
Volumes of most substances decrease as the temperature decreases, but there is a limit to how much something can shrink.

3. Weather, Lesson 5 Absolute Zero
Theoretically, the lowest temperature possible would correspond to a volume of zero.
Lets look at an example. The volume of a gas inside a flexible container is measured as the gas is cooled.
Several data points are plotted on a graph.

4. Weather, Lesson 5 Absolute Zero

5. Weather, Lesson 5 Absolute Zero
As the temperature decreases, the volume decreases in a predictable way.
The data points lie close to a straight line, and by extending this line to the
x-axis, you can determine the theoretical temperature of the gas zero volume.
This is called absolute zero. We still have not been able to reach this temperature.

6. Weather, Lesson 5 Absolute Zero
Very precise measurements show that °C is the lowest temperature possible, or absolute zero.
Kelvin Scale
If you want to create a scale where the temperature is 0 when the volume is 0, you must add 273 to each temperature.

7. Weather, Lesson 5 Absolute Zero
This new scale was proposed by Lord Kelvin in 1848.

8. Weather, Lesson 5 Absolute Zero
The Kelvin is the same size as one Celsius degree, and the formula that relates Celsius to Kelvin is
K = C or C = K – 273
To convert 30°C to kelvin, add 273.
(303 K)
We do not use the degree symbol°, with the Kelvin scale.

9. Weather, Lesson 5 Absolute Zero
If we consider room temperature as 68°F, which converts to 20°C, then what is this temperature in Kelvin?
[(68°F – 32) ÷ 1.8] = 293 K
Molecules in Motion
Gases are very different from solids & liquids. How are they different?
There are no forces that hold gas atoms or molecules together.

10. Weather, Lesson 5 Absolute Zero
To explain the behavior of gases, scientists rely on a model called the kinetic theory of gases.
This theory states that gases are in a constant state of motion, and that gas particles move with different speeds.
Temperature can be defined as a measure of the average speed of gas particles.

11. Weather, Lesson 5 Absolute Zero
As temperature increases, the average speed of gas particles increase.

12. Weather, Lesson 5 Absolute Zero
Scientists hypothesize that if you could cool a substance down to absolute zero, the atoms in that substance would stop moving.
In 2003, researchers at MIT set the current low temperature record of 450 picoKelvin.
or K

13. Review Questions 1. What is absolute zero?
2. What is the coldest temperature ever recorded in the USA? Google to find out where.
3. Where were the coldest temperatures ever found?
4.What is the formula that relates to Kelvin?
5. Solve. What is 78’ C in Kelvin? What is 378 Kelvin in ‘C? What is 58’ F in Kelvin?
6. Explain the kinetic theory of gases.

14. Part 2: Warm and Cold Fronts
We will now investigate the movement of air masses and their role in determining the weather.
How do weather fronts affect the weather?
2 ways: air density and temperature

15. Air Density
Small air masses: When a small sample of a gas gets warmer, it expands to fill a larger volume.
The number of molecules does not change, but the space between them does.
Density= mass divided by volume or D=m/v, decreases because the same mass (m) is divided by a larger volume (V), resulting in a smaller number.

16. Air Density
Large Air Masses: Changes in density for liquids and solids is very small, however, for a gas it is much larger.
When air gets warmer it expands and rises because warm air is less dense than colder air.

17. Weather Fronts
Warm and Cold air meet: Causes 2 weather conditions to happen. Cold and Warm Fronts.
Cold Fronts
A cold front occurs when cold air overtakes warm air.
Warm air is pushed up, cools and forms clouds.
Heavy rains are associated with cold fronts.
The clouds are nimbus (thick) and are similar to the clouds seen before thunderstorms
Cold fronts cause: squalls, tornadoes, strong winds and other destructive weather.

18. Cold Front Visual

19. Cold Front Visual

20. Cold Front Visual

21. Weather Fronts Warm Fronts.
A warm front occurs when warm air overtakes cold air.
Warm air flows up because it is less dense than cold air.
The warm air cools at higher altitudes and water vapor condenses to form clouds.
Thick, low clouds can be seen that will have a steady, light precipitation (rain)

22. Warm Front Visual

23. Warm Front Visual

24. Fronts
Fronts occur at the boundaries between warm and cold air masses.
Clouds and steady light rain form ahead of a warm front.
Clouds and heavy rain form at and behind a cold front.
On weather maps, L’s (low pressure) are associated with fronts (storms and cloudy skies); while H’s (high pressure) are away from fronts and are associated with clear skies

25. Fronts
When air masses form over Earth, they get their properties from whatever is beneath them.
Air masses forming over water tend to be full of moisture.
Air masses forming over land tend to be dry
Air masses that stop moving and stay in one place for a long period of time, can lead to flooding or drought.

26. Summary Cold and Warm fronts cause clouds and precipitation.
The temperature, cold or warm, determines the weather; steady and light (warm) or sudden heavy showers (cold)
Cold air sinks because it is more dense than warm air.
Warm air rises because it is less dense than cold air.

27. Summary
Weather and gases that make up Earth’s atmosphere change density and temperature as they move. Physical changes of matter cause our weather. Most matter expands when heated and contracts when cooled. When heated enough matter changes phase, from solid to liquid to gas. The density of gases is lower than density of liquids or solids. Therefore, changes in density and temperature play a role in the weather.

28. Review Questions 1. Explain why hot air rises.
2. What is the difference between a warm front and a cold front?
3. What causes our weather?
4. What is 50’ F in Kelvin? (F-32/ )
5. Google this: How does a density thermometer work?
6. Think about it! Nearly eighty percent of the air in our atmosphere is nitrogen gas, N-N, while water vapor makes up only 1% of the air. Why doesn’t it rain liquid nitrogen instead of rainwater?

29. Review Questions
7. What is the formula for Density? What is the density of a gas if the mass is 5g and the volume is 25 mL?
What do cold fronts cause?
Density and volume are what type of relationship?
What type of pressure system do we have outside right now?