Download 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 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.
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.
Weather, Lesson 5 Absolute Zero
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.
Weather, Lesson 5 Absolute Zero
• 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.
Weather, Lesson 5 Absolute Zero
• This new
scale was
proposed by
Lord Kelvin in
1848.
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 + 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.
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.
Weather, Lesson 5 Absolute Zero
• As temperature increases, the average
speed of gas particles increase.
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 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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