How do variations in temperature and densityyp affect ... · How do variations in temperature and densityyp affect earth processes? ... density temperature ... •Does the air in

How do variations in temperature and density affect earth processes? y p

………..  modelling convection currentsg

INTRO?INTRO?

• Do you know what a current is?Do you know what a current is?

h h ?• Where have you seen currents?

• What is a current?What is a current? a current is directional movement over a 

distance of a fluiddistance 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 tabletoptabletop.

2. Arrange 4 upside down plastic cups.  These cups will support your plastic 

cup cup

cupp pp y p

pan.

3. Fill your plastic pan 1/2 full of tap water and place it on top of the upside

papercup

water and place it on top of the upside down cups.

4. Set your pan up with fresh steaming4. Set your pan up with fresh steaming hot water at the center of the pan. 

5. Predict what will happen when you  hotwater

drop of food coloringpp y

place a drop of food color placed in the center of the bottom of the pan?

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• CAREFULLY 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 l l l d f ll h dcolor; slowly and very carefully remove the eyedropper.  

• Observe and record what happenst th d f f d l Uto the drop of food color.  Use arrows to show the general path taken by the drops of food color  drop of food coloring

hotwater

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 pancenter of the pan. 

• Predict what will happen if you place a drop of food color in the

hotwater

drop of food coloringdrop of food coloring

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 thebottom near to the edge of the pan as shown below (DO NOT put the drops in yet)

Density, heat and convection (2)Density, heat and convection (2)

• Ever so gently and carefully place a drop of one food g y y p pcolor 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 ththe pan. 

• Observe and record what happens to the drops of food lcolor. 

• Use arrows to show the general path taken by the drops of food  color in your sketch

hot

drop of food coloringdrop of food coloring

hotwater

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 ofthe pan and a baggie filled with ice under the opposite end of the pan. 

• Predict what will happen if you place a drop of food color in• Predict what will happen 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 pfood color just above the ice. 

• Observe and record what happens  to ppthe drops of food color hotice

food coloring

Further ExplorationFurther Exploration

• Ice meltingIce melting• Salinity

i d• Wind

What just happened?What just happened?

Find a partner from another group and together come up p g p g pwith an explanation of what happened.  Create a diagram or a story that explains how the currents formed, and the evidence behind your explanationevidence behind your explanation.Be sure to use the following words:

densitydensitytemperatureenergygycauseeffect

Quick summary: y

Currents = mass movement of water

There are vertical and horizontal currentsThere are vertical and horizontal currents

Mass flow of ocean water is driven by:

wind t ttemperature

salinitygravityg y

Why do we care?

“The Great Ocean Conveyor”

f h f l l– Transfer heat from tropical to polar regions– Influence weather and climate– Distribute nutrients and oxygen

Scatter organisms– Scatter organismshttps://www.youtube.com/watch?v=SdgUyLTUYkg

How good is our model?How good is our model?

Can we apply what we learned to the f ?movement of air in a room?

Review of key conceptsReview of key concepts

1. Density is affected by transfer of heat 

2. Density differences create convection currentse 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), deepincluding wind (creating surface ocean currents), deep ocean currents and weather patterns

4 Convection also occurs inside the earth (in the mantle) and4. Convection also occurs inside the earth (in the mantle) and helps drive plate tectonic motion 

Summary of Key ConceptsSummary 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 temperaturesthan 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 substancesubstance.     

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 alsoBreezes also arise due to 

huneven heating of the Earth’s 

surface

(5)  Solar Heating

and uneven heating of the earth’s surface

The Solar Heating of Earth Varies with LatitudeLatitude

Uneven solar heating helps govern the l b l i l ti f iglobal circulation of air and water.

• Deeper currents are driven by convection currents based on caused by differences in density due to temperature 

d li itand salinity.• Surface currents in the oceans, however, are driven by 

the windsthe winds

The same process drives plate t t i !tectonics!

• Heat travels in convection currents in the mantle. This ll th lith h tallows the lithosphere to move.

• Most of the heat that drives the plates is generated by radioactive decay given off when nuclei of unstableradioactive decay, given off when nuclei of unstable elements break apart.

Challenge – using what you know about density heat and convection how dodensity, 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 amove 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 lt t i t th i kl ? Wh dsalt water mix together quickly?  Why do you 

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 endthe end

VocabularyVocabulary 

• States of matter: solid, liquid, gas• Mass• Volume

D it• Density• Heat• TemperatureTemperature• Convection • Wind• Ocean surface currents• Plate tectonics 

Heat vs. TemperatureHeat vs. Temperature

Heat is energy produced by the random vibrations of atoms or molecules. eat s e e gy p oduced by t e a do b at o s o ato s o o ecu esHow many/ how rapidly molecules are vibrating

Temperature is an object’s response to input or removal of heat. Measure of how rapidly molecules are vibratingof how rapidly molecules are vibrating

Which has a higher temp.?

Which has moreWhich has moreheat?

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!and burst bottles in the freezer!

• When ice forms, salt is excluded h l i l• Water at the poles is very salty

• As ice melts, the water becomes fresher Red = saltier, blue= fresher water

CurrentsCurrents• Does the air in the atmosphere stay in the 

lsame place?  How do you know? 

• Does the water in the oceans stay in the same place? pHow do you know? 

Currents• Does the air in the atmosphere stay in the same place?• Does 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 

ll d tiprocess called convection.