Part 1: Weather, Lesson 5 Absolute Zero

Part 1: Weather, Lesson 5 Absolute Zero

o What is the coldest temperature you have ever experienced?

o What is the coldest temperature ever recorded in the USA?

o -79.8°F or -80*F You can Google it!!o Researchers have recorded temperatures

of -235°C on the surface of Triton, a moon of Neptune.

Weather, Lesson 5 Absolute Zero

o How cold can it get?o To answer this question we will explore

Absolute zeroKelvin ScaleMolecules in Motion

Absolute Zero• Volumes of most substances decrease as the

temperature decreases, but there is a limit to how much something can shrink.


• 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.



• 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.


• Very precise measurements show that -273.15°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.


• This new scale was proposed by Lord Kelvin in 1848.


• The Kelvin is the same size as one Celsius degree, and the formula that relates Celsius to Kelvin is

K = C + 273 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.

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] + 273 = 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.


• 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.


• As temperature increases, the average speed of gas particles increase.


• 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 0.00000000045 K

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.

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

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.

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.

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.

Cold Front Visual

Cold Front Visual

Cold Front Visual

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)

Warm Front Visual

Warm Front Visual

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

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.

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.

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.

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/ 1.8 + 273)• 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?

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?8. What do cold fronts cause? 9. Density and volume are what type of relationship?10. What type of pressure system do we have

outside right now?

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Part 1: Weather, Lesson 5 Absolute Zero