Category: elementary

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Friction for Children: 4 Tricks to Help Children Understand Friction

By Lorie Moffat

If you’re looking for ways to aid in teaching friction for children then keep reading. So your child comes home from school with questions about friction. How can you help your child understand this concept? Without friction life as we know it would not exist. Every surface would be more slippery than ice. You could not walk, run, write, or even feed yourself without friction. Friction for children is as easy as using common examples to guide your explanation.

Friction for children starts with the basics. Friction is a push, pull, or a force which works against the motion of objects that are in contact as they move past each other. When objects are touching their surfaces tend to stick together, like the tiny loops and hooks of Velcro. Heat and sound are also produced by friction. If you rub the palms of your hands together quickly your hands get warm and you can hear the sound that friction creates.

There are three types of friction; sliding friction, rolling friction, and fluid friction. Sliding friction is caused by two objects touching each other that slide past one another. For example, when you push a large wooden crate across a floor you push against sliding friction. The entire surface of the crate that is in contact with the floor slides against the floor, slowing down the motion of the crate. Rolling friction uses wheels. If you move the identical large wooden crate with a wagon then you exert a force against rolling friction. Only the bottom of each wheel is in contact with the floor. Rolling friction is less than sliding friction; it takes less effort to push the crate on the wagon than to push the crate that is directly resting on the floor. When an object is in contact with a fluid, a liquid or a gas this is considered fluid friction. Airplanes and race cars are streamlined to reduce fluid friction. They have smooth, curved surfaces to reduce the friction, called drag, with the air.

When teaching friction for children it’s important to stress how friction can be advantageous. You light a match using friction. As you strike a match, friction creates enough heat to ignite a chemical compound in the match head that then burns the rest of the match head. Automobile brakes work because of friction. As the brake pads rub against the car’s wheels, the car slows down. Shoes designed for some sports have special soles to use friction to your advantage. Baseball shoes and football shoes have cleats to increase friction by sticking to cracks in the ground. A violinist puts rosin on his bow to increase friction between the bow and the violin strings, therefore producing sound.

However, friction can also be disadvantageous. If a door hinge squeaks, the noise is caused by friction. The space shuttle’s nose and wings heat up dramatically as it returns to Earth from orbit. The ceramic tiles on the shuttle’s nose and wings are designed to dissipate this heat caused by friction. The moving parts of a car’s engine rub against each other and can stick together, causing the engine to seize and to stop working. Using oil in a car’s engine protects the parts from friction. Cooked foods tend to stick to pans. Teflon on non-stick cookware reduces friction between the food and the pan, causing the food to slide. Competitive swimmers wear specially designed racing suits to reduce the friction between themselves and the water so that they can swim faster. A bowler wears extremely flat-soled shoes to slide on the lane right before he releases the bowling ball. Silicone aerosols, oils, grease, graphite (the very soft form of carbon in “lead” pencils), and ball bearings are all used to reduce friction.

By using every day examples, you can teach friction for children and help them better understand this concept. The three types of friction, sliding, rolling and fluid, can either be beneficial or detrimental to the motion of objects. Friction between your pen or pencil tip and the paper you write on allows you to write on the paper. Friction between the ground or the floor and your feet allows you to run or walk along these surfaces. Friction between your food and a spoon or fork allows you to eat with these utensils.

Lorie Moffat has 20 years of teaching experience in both public school classroom and science museum settings. Contact her about special summer online tutoring packages.

Source: http://www.homeschool-articles.com/friction-for-children-4-tricks-to-help-children-understand-friction/

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Everyday Science: Contrails

It’s fall, and that means leaves falling, pumpkin pie baking, calendars rapidly filling, and ….. contrails forming.  So what exactly is a contrail?

Contrails (short for condensation trail) are man-made “clouds” created by aircraft engines when the temperature and humidity conditions are just right.  Usually occurring at temperatures below -40°C, and at altitudes above 26,000 ft, contrails are formed when water vapor condenses and then freezes on the particulate matter in aircraft exhaust.  To form a contrail, the temperature must be low enough or the humidity must be high enough for water to condense on the exhaust particles.  Since the process of condensation is well understood, it is possible to predict when contrails will form based on prevalent temperature and humidity conditions.

Typically, with fall weather comes cool, moist air aloft and conditions at are perfect for contrail production.  Think about it: do you see very many contrails in the summer months when it is hot and dry?  Sometimes contrails dissipate rapidly with high winds or high turbulence aloft, and sometimes contrails linger for quite some time.  Contrails dissipate rapidly with low humidity, since the newly formed ice crystals evaporate quickly.  With high humidity, persistent contrails are visible, as ice crystals grow in size, absorbing water from the surrounding (humid) atmosphere.  You might see a contrail which has been stationary for some time right next to one which is dissipating rapidly.  These contrails are at different altitudes, with different conditions at each level.

Since different gas composition, exhaust gas temperatures, and water vapor content exist in different aircraft engines, not all aircraft engines will produce a contrail at the same altitude (with identical weather conditions) at the same time.  Contrail formation has nothing to do with the type of aircraft or its speed.

Another form of contrail is produced when a portion of an aircraft such as a wingtip or winglet causes air cavitation in humid conditions.  Have you ever seen these vapor trails, perhaps at an airshow, when aircraft flying low over the airfield pitch up rapidly in high humidity conditions?  And since we’re mentioning winglets (shown below), you might be interested to know why they’re on the wing.  The winglet serves to reduce aerodynamic drag so the aircraft burns less fuel in flight.  This fuel efficiency is created by breaking up the turbulent wingtip vortices (pronounced VOR-ti-sees) produced by the pressure differential between the bottom and top of the wing.  No vortices = less drag.

Southwest Winglets

Back to the contrails, though… have you ever seen patterns in the sky produced by contrails?  Perhaps all paralleling one another or converging on a point?

This is no coincidence.  The world is criss-crossed with jet routes flown by all aircraft above a certain altitude.  At the junctions of jet routes are navigational aids, which you may have seen while driving or flying yourself.  Here is one navigation aid (navaid) in Oregon, shown courtesy of Wikipedia:

The aircraft whose contrails you see are each navigating with navaids similar to the one shown above.  Therefore the aircraft fly over the navaids as they transit the jet routes.  Parallel tracks of contrails are aircraft flying along the same route.  If you are ever curious about a contrail track you observe, you can check http://flightaware.com.  A screen shot near Dallas, Texas shows multiple aircraft tracks transiting along an east-west jet route using navaids.

Contrail predictions have been used since WWII, when the ability to spot enemy aircraft “conning” could make the difference in advance notice of an airstrike or positioning for air combat.  Here’s a graphic from p. 55 of the March 1943 edition of Popular Science identifying two types of vapor trail formation:

How about an activity to predict contrail formation?  NASA has an activity page where you can access  an Appleman chart.  Using the chart, you can construct a temperature profile to forecast contrail activity in your area.  The activity (recommended for 5th grade and up) begins this way:

…”Military planners have been interested in condensation trail (contrail) forecasts since World War II. Contrails can make any aircraft easy to locate by enemy forces, and no amount of modern stealth technology can hide an aircraft if it leaves a persistent contrail in its wake. In 1953, a scientist named H. Appleman published a chart that can be used to determine when a jet airplane would or would not produce a contrail. For many years, the US Air Force Global Weather Center used a similar chart to make contrail forecasts.

The first published reports of contrail formation appeared shortly after World War I. At first, scientists were not sure how contrails formed. We now know that they are a type of mixing cloud, similar to the cloud that sometimes forms from your breath during a cold winter day. Appleman showed that when the air outside of the airplane is cold enough and moist enough, the mixture of the jet exhaust and the air would form a cloud.

An example of a contrail-forecasting chart is shown below. We will use the chart to make our own forecasts, and make observations to determine whether they are true or false.

Appleman Chart

… Using either the temperature information provided by the teacher or the temperatures obtained from an Internet location (see note below), complete the table on the “Student Data Sheet”, then plot the temperatures corresponding to each pressure level on the “Appleman Chart: Student Graph Worksheet”. Connect the points to create a temperature profile of the atmosphere.

Note: Temperature and humidity information can be obtained from weather balloon soundings launched twice a day from several locations around the country. Several locations on the Internet including http://weather.uwyo.edu/upperair/sounding.html provide detailed sounding information. Choose the location nearest your school.”

This activity would make a perfect accompaniment to a physical science class, a weather unit study, or just a fun diversion.  If you have a weather station in your home, it would pair up nicely as an associated activity.  For younger elementary students, the NASA site also has a word search and a downloadable “Clouds and Contrails” craft.  Have fun!

Resources:

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Fossils: Stones and Bones, part 3: Searching for Fossils on the Internet

Use these helpful resources as you study fossils in your homeschool!

Fossil Sites and Collecting Locations
Straight-forward list by state.
http://www.fossilsites.com/index.html

Fossils for Kids
Great, creative website with fun things like the X Marks the Spot page, Now and Then (my favorite), and a Shark Teeth collection!
http://www.fossilsforkids.com/

St. Louis Science Center
Nice museum site: fossils, dinosaurs, and many other topics.
http://www.slsc.org/Home.aspx

The Creation Museum
70,000 square foot museum in Kentucky that brings the pages of the Bible to life!
http://creationmuseum.org/

San Diego Natural History Museum: Finding Fossils
Kids’ site on the who, what, when, where, why of fossils
http://www.sdnhm.org/kids/fossils/index.html

Fossils, Rocks, and Time
Produced by the US Geological Survey, a very informative site for your older students
http://pubs.usgs.gov/gip/fossils/contents.html

Everything Fossils…Fossil Facts and Finds
An educational site that tells you everything you need to know about fossils, including activities, coloring pages, specific dinosaur information, articles, links, and lesson plans
http://www.fossils-facts-and-finds.com/

Black Hills Institute of Geological Research, Inc.
“the leader in paleontological excavations and preparation since 1974, BHI has been helping supply museums and collectors the finest in professionally prepared fossils and cast replicas.”
http://www.bhigr.com/

United Kingdom Natural History Museum: Dino Directory
Online guide to 333 dinosaurs, images, and classroom activities with printable data files.
http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/

Champlain Sea Fossils
See pictures of sea fossils from Canada.
http:www.geo.ucalgary.ca/~macrae/t_origins/champlain/champlain.html

Collecting Fossils in California
All you need to know if that’s the state you hail from- check it out!
http://www.gtlsys.com/

Fossilicious.com
You can purchase fossils from this outfit: specializing in low-cost, quality fossils.
http://www.fossilicious.com/

Fossil Lesson Plans from Dinosaur Train!
I couldn’t resist.  I will definitely be using this with my little Dinosaur Train fanatic.
http://www.pbs.org/teachers/dinosaurtrain/lessonplans/fossils/

Print Resources:

An Illustrated Guide to Fossil Collecting by Richard Casanova and Ronald P. Ratkevich.  A fundamental book on fossils and fossil collecting, it starts out with a brief history of collecting incuding some of the famous collectors of the past like Mary Anning who was twelve when she found a complete skeleton of Ichthysaurus.  Following a description of fossils and  how they are formed, is a discussion of fossil classification.  Sounds technical but it is written for the real person who collects for his or her own bookshelf.  There is a generic chapter on the history of the Earth, evolutionary, of course, but written from the ecological standpoint.  Chapters on how to collect and display your fossils are included.  Lists of resources with museums, geological surveys, societies and paleontological libraries finish up the book.  The best chapter in number seven.  This is the chapter on fossil collecting localities in North America.  This is definitely the resource you need to find fossils on your vacation trips.  Recommended for all ages.

Dry Bones…and other fossils by Gary Parker.  A Master Books publication, this one is written from a Creationists viewpoint.  It is a dialog between Dr. Gary Parker and his family on a typical fossil hunting trip in Indiana, Dr. Parker covers most of the bases in the creationist story of the Earth from creation to the big flood, explaining fossils and how they are made.  This book also comes in a read-along tape version for your little ones.

The Illustrated Origins Answer Book  by Paul S. Taylor.  A wonderful reference book for older readers, the Answer Book has two parts: a textbook and a reference section.  The text is very concise having good definitions which are not oversimplified on the page the word occurs.  This book is not for young children, but for interested adults and older children who have been wondering about some little problem with scientific creationism, but didn’t know where to look.  There many quotes from scientists, creationists as well as non-creationists, in the reference section.  A handy reference for creationists who may become involved in debates or lively discussions.


Field Guide to North American Fossils by Ida Thompson.  Photographs!  In color!  This field guide claims to be the first all-photographic one published. Written for the field, the guide is valuable to have in your field pack so that you can identify that odd fossil without losing face before your children.  Actually, any age can use this great little guide.  It is, of course, evolutionary and has a description in the first part of the history of the Earth period by period.  There are interesting details of recent research in this discussion, so don’t overlook it just because of the evolutionary bias.  After the photo section is a chapter which uses words to describe the fossils of that type.  The discussions are correlated to the photos.

Roadside Geology Series This series is wonderful for keeping in the car on a trip and reading along as you ride through the countryside.  Most of the major routes through a state are covered in the books and a lot of the minor ones.  Geology is best studied outside and these books help you do that.  They help you figure out what is going on with the Earth as you travel past roadway cuts and outcroppings.  The book for Texas covers the different geographical sections (examples are from Southeast Texas: Upper Gulf coast), the typical landforms (like saltdomes and rivers), the different processes still going on (like longshore drift and hurricanes), and the larger routes (like Interstates 10, 35, and 45)  and US routes (59 and 290) and state routes (36)  The glossary in the back and lots of pictures throughout the text make it simple to understand.  Most states are covered, you can purchase the books at The Geology Store.


Dino-Trekking:  The Ultimate Dinosaur Lover’s Travel Guide   by Kelly Milner Halls.  This is another traveling book, but you’ll use it before you get in the car.  Well-known and not so well-known dinosaur sites are listed and described here.  In the margin are the details like address, admission prices, and facilities available. There are side boxes with interesting notes from the curators of some of the museums and parks. The last section is a description of many dinosaurs plus a few non-dinosaurs which are included.  Useful for dinosaur lovers.