How do variations in temperature and density affect earth processes? y
p
……….. modelling convection currents
g
INTRO?
• Do you know what a current is?
Do you know what a current is?
• Where have you seen currents?
h
h
?
• What is a current?
What is a current?
 a current is directional movement over a distance of a fluid
distance of a fluid
• Where have you seen currents?
 rivers, the ocean, wind…….
• What causes currents?
Density, heat and convection (1)
Build the model: 1. Place a piece of white paper on the tabletop.
tabletop
2. Arrange 4 upside down plastic cups. These cups will support your plastic p
pp y
p
pan.
cup
cup
cup
paper
3. Fill your plastic pan 1/2 full of tap water and place it on top of the upside
water and place it on top of the upside down cups.
4. Set your pan up with fresh steaming 4.
Set your pan up with fresh steaming
hot water at the center of the pan. pp
y
5. Predict what will happen when you place a drop of food color placed in the center of the bottom of the pan?
hot
water
drop of food
coloring
Density, heat and convection (1)
y,
( )
• Place a piece of white paper behind your pan so that you can see the movement of the food coloring better. • Use your eyedropper to get a drop of food color. • CAREFULLY place the tip of the eyedropper at the bottom place the tip of the eyedropper at the bottom
of the middle of the pan. Once the eyedropper tip is at the bottom, GENTLY and SLOWLY squeeze out the food color; slowly and very carefully remove the eyedropper. l
l l
d
f ll
h
d
• Observe and record what happens
t th d
to the drop of food color. Use ff d l
U
arrows to show the general path taken by the drops of food color drop of food coloring
hot
water
Density, heat and convection (2)
• Dump out your water and get a pan of clean tap water. • Set your pan up with fresh steaming hot water under the center of the pan
center of the pan. • Predict what will happen if you place a drop of food color in the
place a drop of food color in the bottom center and place another drop of a different color at the bottom near to the edge of the
bottom near to the edge of the pan as shown below (DO NOT put the drops in yet)
drop of food coloring
drop of food coloring
hot
water
Density, heat and convection (2)
Density, heat and convection (2)
• Ever so gently and carefully place a drop of one food g
y
yp
p
color in the bottom of the center of your pan and a drop of the other food color at the bottom near to the edge of the pan. th
• Observe and record what happens to the drops of food color. l
• Use arrows to show the general path taken by the drops of food in your sketch
color drop of food coloring
drop of food coloring
hot
water
Density, heat and convection (3)
• Set your pan up with fresh steaming hot water at one end of the pan and a baggie filled with ice under the opposite end of
the pan and a baggie filled with ice under the opposite end of the pan. • Predict what will happen
Predict what will happen if you place a drop of food color in if you place a drop of food color in
the center of the pan and another drop of a different color just above the ice as shown below (DON’T put the drops in yet)
• Ever so gently and carefully place a drop of one food color in the bottom of the center of your pan and a drop of the other y
p
p
food color just above the ice. pp
• Observe and record what happens the drops of food color
to ice
food coloring
hot
Further Exploration
Further Exploration
• Ice melting
Ice melting
• Salinity
• Wind
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What just happened?
What just happened?
Find a partner from another group and together come up p
g p
g
p
with an explanation of what happened. Create a diagram or a story that explains how the currents formed, and the evidence behind your explanation
evidence behind your explanation.
Be sure to use the following words:
density
temperature
energy
gy
cause
effect
Quick summary: y
Currents = mass movement of water
There are vertical and horizontal currents
Mass flow of ocean water is driven by:
wind
t
temperature
t
salinity
g
gravity
y
Why do we care?
“The Great Ocean Conveyor”
–
–
–
–
Transfer
f heat
h
from
f
tropicall to polar
l regions
Influence weather and climate
Distribute nutrients and oxygen
Scatter organisms
https://www.youtube.com/watch?v=SdgUyLTUYkg
How good is our model?
How good is our model?
Can we apply what we learned to the movement of air in a room?
f
?
Review of key concepts
Review of key concepts
1. Density is affected by transfer of heat 2. Density differences create convection currents
e s ty d e e ces c eate co ect o cu e ts
3. Convection currents affect atmospheric circulation, including wind (creating surface ocean currents), deep
including wind (creating surface ocean currents), deep ocean currents and weather patterns
4 Convection
4.
Convection also occurs inside the earth (in the mantle) and also occurs inside the earth (in the mantle) and
helps drive plate tectonic motion Summary of Key Concepts
Summary of Key Concepts
 Density is affected by transfer of heat  water and air at higher temperatures are less dense than water and air at low temperatures
than water and air at low temperatures
 Density differences create convection currents
,
 warm fluids are less dense and will rise,  cold fluids are more dense and will sink
 water from the sides flows in to fill the space
 This results in a convection current.
This results in a convection current
 Deeper ocean currents are caused by convection (
(temperature, and salinity)
p
,
y)
 Convection currents also influence atmospheric circulation, including wind, weather and ocean surface currents
 Convection occurs inside the earth (in the mantle) and helps drive plate tectonic motion How does this work?
(1) Differential heating affects density
To understand density we need to know:
Mass = amount of matter (how much stuff) What is the difference between Mass and Weight? Volume = how much space you have (2) Density matters!
(2) Density matters! Density is a key concept for understanding Earth processes. Density measures the mass per unit volume of a substance. substance
Density = _Mass_ Volume
(3) Temperature Affects Density
The relationship of density to temperature for pure water.
(4) Differential heating & cooling create density differences.
Convection currents = movement caused by differential heating and cooling
Breezes also Breezes
also
arise due to uneven heating h
of the Earth’s surface
(5) Solar Heating
and uneven heating of the earth’s surface
The Solar Heating of Earth Varies with Latitude
Uneven solar heating helps govern the global circulation of air l b l i l ti
f i
and water.
• Deeper currents are driven by convection currents based on caused by differences in density due to temperature and salinity.
d li it
• Surface currents in the oceans, however, are driven by the winds
the winds
The same process drives plate t t i !
tectonics!
• Heat travels in convection currents in the mantle. This allows the lithosphere to move.
ll
th lith h
t
• Most of the heat that drives the plates is generated by radioactive decay given off when nuclei of unstable
radioactive decay, given off when nuclei of unstable elements break apart.
Challenge – using what you know about density heat and convection how do
density, heat and convection, how do you expect air to move in this image?
Some things to think about…..
Some things to think about…..
• What similarities are there in how water and air at s a t es a e t e e
o
ate a d a
move around Earth? Why do you think this is so? • When freshwater from a river flows into an ocean, do you think the freshwater flows to the bottom, stays near the top, or do the fresh and salt water mix together quickly? Why do you lt t
i t th
i kl ? Wh d
think that?
• Evaluate the statement: Hadley cells and the Evaluate the statement: Hadley cells and the
movement of tectonic plates have nothing in common.
the end
the end
Vocabulary Vocabulary
•
•
•
•
•
•
•
•
•
•
States of matter: solid, liquid, gas
Mass
Volume
D it
Density
Heat
Temperature
Convection Wind
Ocean surface currents
Plate tectonics Heat vs. Temperature
Heat
eat is
s energy
e e gy produced
p oduced by the
t e random
a do vibrations
b at o s of
o atoms
ato s or
o molecules.
o ecu es
How many/ how rapidly molecules are vibrating
Temperature is an object’s response to input or removal of heat. Measure
of how rapidly molecules are vibrating
Which has a
higher temp.?
Which has more
heat?
Water Becomes Less Dense When It Freezes
Water expands about 9% as the
crystal forms. That’s why it floats
and burst bottles in the freezer!
• When ice forms, salt is excluded • Water at the poles is very salty
h
l i
l
• As ice melts, the water becomes fresher Red = saltier, blue= fresher water
Currents
• Does the air in the atmosphere stay in the same place? l
 How do you know? • Does the water in the oceans stay in the same p
place? How do you know? Currents
• Does
Does the air in the atmosphere stay in the same place? the air in the atmosphere stay in the same place?
How do you know? • Does the water in the oceans stay in the same place? Does the water in the oceans stay in the same place?
How do you know? In this activity we will learn about a major reason that air in the atmosphere and ocean water move around. It is a process called convection.
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ti