ingridscience

Introduction to the activity for the teacher:
Shoes are manufactured with many different soles, depending on the function of the shoe. (For example, runners have rubberized and inundated surfaces to grip the ground, whereas tap shoes have slick metal soles to enable the dancer to click out a rhythm and slide on the dance floor.) Friction is the force that counteracts a shoe and surface sliding past each other, caused by the surfaces rubbing against each other. A flat sole or a polished floor will generally reduce the friction between shoe and floor as the flat surfaces slide past each other more easily. But friction is a complex force determined not only by the roughness of the surfaces, but also by how hard the surfaces are pushed together (for example by the weight in the shoe), the chemical material that the surfaces are made of and whether there is any fluid between the surfaces. In addition, the force of friction opposing an object starting to move (“static friction”) is different from the friction once an object is moving (“kinetic friction”). Refs 1 and 2.
Pulling different shoes across different surfaces provide a system that is easy to set up and can explore all these aspects of friction.

Review or introduce friction with students:
The force between two materials, that stops them from sliding past each other. Two surfaces that slide past each other every day are the bottom of a shoe and a floor. Tell students that they will be measuring the friction between their shoes and the surface of their desks to start, before exploring other surfaces.

Measuring friction in different shoes:
Show students how to measure the friction between a shoe and their desk, by hooking the spring scale through a strap or lace on the front of the shoe, then using it to pull the shoe along. They should pull the shoe slowly but steadily until a consistent reading is obtained. It is often easier to have one person focusing on pulling the shoe while another reads the scale.
Show students the worksheet “Friction with different shoes” (page 1 of the attached worksheet), and indicate where they will place their friction data for one shoe type with no weight, the smallest weight they have (e.g. 200g) then the larger weight (e.g. 500g), before trying a different shoe. The weight should be placed at the back of the shoe over the heel (for consistency among the groups)
Allow students to choose their shoes and take their readings, but makes sure that each group tries a cleat, tap shoe, or other shoe with a slick sole.
Students will need a circulating adult to check that they are measuring sliding friction (as the shoe is moving) and not static friction (as the shoe just starts to move), as static friction will be a lot higher and give inconsistent class results.
Once all groups have readings for at least two shoe types, ask students to graph their data on the graph paper worksheet or on the board.
Discuss results, some points to be made follow:
Students should find that for every shoe, increased weight caused an increase in the friction. Why is this? If the shoe and the surface are pressed together more firmly, the tiny bumps and indentations in the shoe and surface get caught up in each other more so increasing the friction.
Expected results and discussion:
The shoes will vary in their friction, sometimes in surprising ways. In general though, tap shoes or other slick dance shoes will have less friction, cleats will have less friction, and some (though not all) worn out runners will have less friction. Discuss these results, including comments on how flat the surfaces are (tap shoes are very hard and flat, worn out runners can be very flat) and how large the contacting surfaces are (cleats are hard plastic and only contact the table in small spots). Also discuss the materials that the shoes are made of. Some runners have soles that are rubberized, which is a tacky material which sticks to surfaces and is hence high friction.

Measuring friction on different surfaces:
Tell students that they will be measuring the friction between one shoe and several different surfaces.
Distribute different surfaces around the classroom and point out other surfaces already in the classroom e.g. carpet, cardboard sheet, a piece of foam, a layer of sand in a tray, a tray of ice, pillow.
Tell students that their group should choose one shoe and one weight, and measure the friction on different surfaces. They should start with the desk top once again, then move to different surfaces. Using the worksheet “Friction with different shoes” (page 2 of the attached worksheet), they record the friction for each surface, as well as the change in friction from the desktop in each case.
Note: as the students work, the ice tray will need to be maintained - pour off the excess water so that the shoes are moving across the ice, not a puddle of water.
Expected results and discussion:
Ask students which surfaces decreased the friction and which increased the friction, or ask them to chart their results on a common graph (see photo - note the results will likely be a little messy). As a class try and figure out possible reasons. Some are listed here:
Carpet and foam - the carpet and other knobbly surfaces have lumps and bumps which get caught up in the (sometimes tiny) bumps in the sole of the shoe and increase friction. Foam may give differing results, depending on what kind it is - although bumpy it may have a slick texture that can make surfaces slip past each other and so decrease the friction.
Sand - sand in a thin layer will likely decrease friction. This is because the individual grains can roll. Rolling is a low friction motion, as the surfaces do not slide past each other but rotate past each other. Students can relate to marbles on a floor and how their rolling motion can be hazardous if stepped upon. If the sand is deeper, the friction may increase.
Ice - if there is a very thin layer of water on the ice, the liquid will fill the bumps and grooves on the sole of the shoe, allowing it to slide over the ice more easily, hence reducing the friction. Lubricants such as oil, grease and wax work in the same way to reduce friction between moving parts of a machine or other object. With more water on ice, the friction may increase as the shoe has to push through the puddle.

Closure Discussion
Friction is a complex force that resists objects sliding past each other. We use products that have increased friction, for example to stop our shoes slipping, or to brake a bike. We also use products that have decreased friction, such as dance shoes that can slide across a floor, low-friction ice skates lubricated by the thin layer of water between the ice and skates, or oil to lubricate moving parts on a machine.

Thank you to Brenda Koch, then from Xpey’ Elementary, for teaching Ingrid how to twine.

Twining is a method of twisting strands around each other, used by BC Indigenous People, as well as many other cultures worldwide, for making ropes, fishing lines and nets, as well as for binding the thicker strands of a basket, hat or mat together.

Teach students how to twine. It is easier to start with grass, as it is stiffer and holds in place more easily than wool.
Lay two grass blades side by side and tape securely to the desk. Twist the right hand strand twice to the right (using the right hand, so that the thumb rotates over the top of the hand). Pass the right hand grass blade over the left hand blade and hold in your left hand (without letting it untwist). Twist the new right strand, then pass over the new left hand strand. Repeat down the length of the strands, not too tightly, so that the strands relax into each other to make a coil.
Optional: A twined strand can be twined again around another one, to make a stronger cord.
Twine wool with contrasting wool colours, to make a twisted pattern that can be used as a bracelet, hair piece or to hang on their backpack. The twisting motion each time is in the same direction as the twist already on the wool.

The physics in twining:
When you twist, you force the grass or wool to twist into a new position. You are putting energy into it - elastic potential energy - a stored energy in materials that are elastic and can deform. When you let go, the elastic energy is released and the wool tries to unwind again. As it is twisted around the other strand, they tighten onto each other to keep the coil in place.

Twined roots make strong fishing line or basket handles.
When strands are twined around uprights, they can make baskets or hats or other objects.
Students can try weaving in and out of small branches to mimic basket-making. Securing everything on a clip board helps.
Look at twined objects e.g. clam basket or Haida hat photos (twined so tightly it is waterproof).

Great to do this activity outdoors, near native grasses and plants that are used for twining and weaving.
At Trout Lake we found:
Willow bark (used for ropes, fishing line and nets) and willow branches for making a fish weir (they take root in the river bottom). Small flowered bullrush for basket weaving. Cedar for woven bark (clothing). Iris leaves are woven into snares strong enough to catch elk and large animals.

The inner bark of the Western Red Cedar tree is often used for twining to make baskets, mats, hats and regalia.
Harvesting cedar bark by Snuneymuxw people, with images:
https://gabriolamuseum.org/connections-from-the-ground-up/
Video of harvesting cedar bark by shíshálh (Sechelt) peoples:
https://www.youtube.com/watch?v=A6KS4J8QyNQ
More information on twining used in basket weaving:
http://www.burkemuseum.org/blog/coast-salish-weaving-tools-technologies

Before the lesson:
Make frames, one per student. Use white glue to make a square from narrow popsicle sticks. Binder clip at each corner over night for a strong frame.

Introduction:
Indigenous people from BC make many kinds of baskets, often in the winter when there is more time.
An important basket is for collecting clams. It is called an open basket as it has holes in it. Clams are thrown in it with sand stuck to them. The basket is dipped in water to rinse off the sand, which is small enough to fall through the holes, while the basket catches the clams.

Make your own weaving to separate glass counters (representing clams) and gravel (the sand that clams are separated from).
Try a kind of weaving called plaiting - alternately under and over. (Kindergarteners may just need to lay across.)
Use pipe cleaners on a frame. Pour the 'clams' and sand over the weaving, to try and catch the clams on the weaving, just as a clam basket catches clams.
To reset after each test, pour the clams and sand from the tub they fell into, back into the dixie cup.
Note: clam baskets woven by the Coast Salish are more often made by twining, another weaving technique, rather than plaiting.
See the Twining activity for how to twine and a short beginner of twining around uprights (which is how clam baskets are often made).

Look at pictures of a clam basket.
Search for clam basket in the Museum of Anthropology at UBC:
http://collection-online.moa.ubc.ca/search?keywords=clam+basket
Or try these weblinks:
http://ww2.glenbow.org/search/collectionsSearch.aspx then search AA 1817 (for a picture of a beautiful clam basket, including close up images).
http://www.burkemuseum.org/research-and-collections/culture/collections… found by searching "clam basket" in the Burke Museum Ethnology Collections Database: http://www.burkemuseum.org/research-and-collections/culture/collections…
Note that these clam baskets are not made by plaiting, but by twining around the uprights.

If students have already done twining, point out the twining that holds the basket uprights together.

Open (sieve baskets) are also used for catching fish and hulling (sifting the grains from chaff).

Excellent video for post lesson: Ed Carriere (Suquamish) making a clam basket - shows gathering the cedar branches and roots, splitting them and weaving them https://vimeo.com/37561426 (15 minutes long) and article on the same process: https://hakaimagazine.com/features/the-basketmaker/

More information on basket weaving:
http://www.burkemuseum.org/blog/coast-salish-weaving-tools-technologies
From this article: "Weaving is done with only the fingers. Plaiting is done with one horizontal weft yarn passing in front and behind the vertical warp yarns. Twining is done with two horizontal weft yarns one passing in front while the other passes behind the warp. This technique can be used to create a tighter weave and allows for elaborate geometric patterns to be created."

Tell students we will be making a simplified cake to understand the chemistry underlying making a cake.

Introduction as a demonstration:
Ask students what ingredients go into a cake, and for each one write up into colums as flavourings or ingredients needed for the structure of the cake. As flour, liquids and a rising agent are mentioned, mix these ingredients into a well of a muffin tin as a simplified cake batter: about 3 Tablespoons of flour, 3 Tablespoons of water, 1 teaspoon of baking powder. (Egg and milk in a real batter are needed for binding the ingredients together as they are cooked in the oven, but are omitted in our simplified cake batter.)
As discussion continues, the simplified cake batter will rise slowly, and students will start to notice.
Ask them which ingredient made it rise [the baking powder].

Introduction as a short activity for students:
Students each get a tray and a stir stick, and flour and water are in pots with their own scoop.
Ask students to mix a little flour (about 1/4 teaspoon) and water until they make a cake batter consistency, using their stir stick to mix them together.
Then they should add a small scoop of baking powder, mix it up, then wait and watch.
Their cake batter will slowly rise, and some of them will see bubbles appearing.

Continuing:
Tell students that baking powder has three ingredients - read them from the package:
1. cornstarch
2. sodium bicarbonate, which is baking soda
3. monocalcium phosphate and/or sodium aluminum sulfate, which do the same job as cream of tartar.
Ask students to figure out which two of these ingredients mix to make gas, by mixing small scoops of them with water in wells of their tray. If they add the powders to the tray first, the water can be added to mix them together, so the scoops can remain in the pots of powders.
The attached worksheet can help students keep track of what they find.
[Remove flour and baking powder from their tables, and add baking soda, cream of tartar and cornstarch to tables.]

Students should find that baking soda and cream of tartar make bubbles, but the other combinations of two ingredients do not. (Sometimes bubbles arise from the water being squirted in, but these soon pop, and do not count as bubbles being made.) Students may get different results from each other - tell them that this happens to scientists all the time, and they should simply both repeat the experiment until they get consistent results. Sometimes a powder may contaminate a nearby well to give differing results.

Use molecular models to figure out what gas is being made as the baking soda and cream of tartar are mixed and a chemical reaction happens to make gas.
Students are given HCO3 (baking soda) and H (in the cream of tartar). Ask the to rearrange the atoms to make two new molecules. Tell them that one molecule is water (H2O) and ask them to figure out the other one, by joining all the remaining atoms and bonds and filling all the holes in the atoms. They should arrive at CO2, which is carbon dioxide, a gas.

Summarize that when cakes are made with baking powder, the baking soda and cream of tartar (or other acid) in the baking powder mix together in the wet environment of the cake batter. They chemically react to make carbon dioxide gas, which makes bubbles which are trapped within the cake batter. We can see these bubbles as holes in cake. They make the cake light and fluffy.

Test the materials to determine how rigid, elastic and malleable they are. These are the properties of rigid, elastic and malleable materials:
Rigid materials do not deform easily.
Elastic materials can be deformed, then return to their original shape.
Malleable materials can be deformed, and do not return to their original shape.
(Note that technically, I should use the term "plastic" instead of malleable. But as the word plastic is used so often in another context, it would be confusing for students. Materials with plastic properties come in different types: malleable materials can be flattened easily, and ductile materials can be drawn into a long thread easily.)

The classification of the materials will depend on their thickness and shape, for example metal can be quite rigid if it is thick, or malleable if it is thin. Any answer is fine as long as the students are manipulating the materials and thinking about how they deform.
Our results: rigid materials were marble, rock, hard ball, bow tie pasta (spaghetti would be elastic too). Between rigid and elastic were metal strip, popsicle stick, plastic spoon, bouncy ball. Elastic materials were balloon, foam sponge. Between elastic and malleable were styrofoam and pipe cleaner. Malleable materials were play dough and tin foil. Between malleable and rigid is ping pong ball (though nearer rigid than on the photo).

If students are given several types of balls, ask them to see how elastic or rigid they feel, then based on that, predict how high they will bounce. The more elastic balls will generally bounce higher than more rigid balls. The elastic material stores energy as it is deformed, which is released again as it returns to its original shape, giving the ball energy to go higher.

At a molecular level, some of these properties can be explained.
Elastic materials are often made of long molecules that can bend and stretch, then return to their original shape e.g rubber. Elasticity may also be due to air pockets in the material that can be compressed e.g. foam.
Rigid materials will be made up of tightly-bonded molecules that are hard to move past each other. Sometimes rigid materials are brittle, so that with enough stress they break apart suddenly as the bonds are
Malleable silly putty has many weak bonds between long molecules that can be broken, then remade in new positions.

Make a slide with a drop of 2% milk, and place under the microscope.
Wait until the milk has stopped streaming around the slide, and the individual fat droplets in the milk stay within the field of view.
Look closely for the fat droplets jiggling around - caused by water molecules bumping into them!
Brownian motion was the first convincing evidence that atoms and molecules existed.

(Milk is an emulsion, a type of colloid - tiny fat droplets held in the watery parts of milk. The fat droplets are all small enough to stay in the milk, and not settle out as a separate layer.)

This activity adapted from pdf: https://www.acs.org/content/dam/acsorg/education/resources/k-8/science-…

Give students tubs of glue making materials, scoops, water bottles, trays, stir sticks.
Ask them to make the best glue possible, mixing the ingredients in a well of the tray. They should test their glue by putting a blob of it on a cardboard strip, pushing a marble into it, then hanging the strip upside down - the longer the marble holds, the better the glue. Students should count seconds to see how long their marble sticks (one mississippi, two mississippi...)
Distribute worksheets/use board space for students to record the recipes they make, so that they can keep track of their own changes, try others' recipes and start to quantitate the data.
A long-lasting recipe can be taped upside down over the edge of the table so other recipes can be tried while it is hanging - note the time that it was taped along with the seconds counted up to that point. When the marble drops, calculate the seconds elapsed. At the final discussion calculate the stick time for those still sticking - do the math together to calculate the number of seconds from the number of minutes.
Discussion around the data can include how to more accurately measure out the quantities (e.g. use standard teaspoon measures) and to time the sticking-times (use a stop watch), for fair comparison.
Students may well discover that their mixtures work better once they have dried out a bit, for good discussion on how commercial glues often require a drying time until they are full strength.

Acting out the glue molecules:
Flour-and-water glue forms in the same way that dough forms: gluten proteins and starch molecules of the flour are bonded together by water molecules.
Divide the students into two groups, A and B. Each group will make a glue molecule.
Four students in group A link hands in a line to make a long starch molecule. Then other groups of four students make starch molecules, to make a total of two starch molecules in group A and two starch molecules in group B (using a total of 16 of the students in the class).
The remainder of the students will be water molecules.
Ask the two starch molecules in each group (A and B) to line up facing each other, with a space between them.
Then ask the water molecules in each group stand between the starch molecules, and reach out their arms to touch both starch molecules, forming 'bonds' between the starch molecules. As more bonds form, the starch molecules are more fixed in place. In the same way, the glue the students made got thick as water was added to the flour.
Optional: race the As and the Bs. Which starch molecules in flour can combine with water to make a glue the fastest? First make your starch chains, then link them with water molecules.

Discuss how these glues work:
The long molecules in some of the ingredients (starch molecules in flour and cornstarch, and protein molecules (gluten in flour and casein in milk powder) are able to reach into the tiny cracks in the cardboard and hold onto it, like fingers reaching into cracks in a wall. (The smaller sugar molecules of the icing sugar is not so good at making a glue, unless it is made really thick). This mechanical mechanism is just one of the ways that real glues work.

Mechanisms of all types of glues:
The molecules of a glue need to be good at sticking to each other and to the material(s) it is glueing together. There are several molecular processes at work.
Adsorption - the glue and the material have charged molecules that attract each other. It is a weak attraction, but with many of these bonds they can hold the glue and surfaces of the material together.
Mechanical - the long molecules of the glue creep into the tiny holes in the surface of the material(s) and hold them together.
Diffusion theory. The adhesive can diffuse into the surface and vice-versa, with molecules swapping over at the join and mingling together.
Chemisorption - there is a chemical reaction between the glue and the material. (not the mechanism for the glues made in this activity)
From www.explainthatstuff.com/adhesives.html

This activity is from the Children's Museum of Houston: https://www.cmhouston.org/classroom-curriculum/stretch-your-potential-2

Fold the elastic band flat.
Tape one end of the flattened elastic band to the end of the skewer, making the tape really tight around the skewer, so that the elastic band is held on firmly.
Slide the straw onto the other end of the skewer.
Lay the free end of the flattened elastic band over the straw and tape tightly to secure the elastic band to the straw, but without taping the straw to the skewer.

Hold the jumper upright on the desk and pull the straw down to the desk so that the elastic band is stretched.
Make sure your head is back (not over the jumping stick).
Let go of the device in one go, by separating your fingers wide quickly.
It will jump in the air by a metre or more.

Students need to be instructed on using it safely - do not jump it towards anyone.

Students enjoy games with their jumping sticks (see photos) after discussion of the science.

For energy transformation discussion:
Ask students to think about the chain of energy transfer that happens as the toy is used.
Chemical energy - from our hands as they pull down on the toy
Motion energy - as the toy is pulled down
Elastic energy - as the elastic band is stretched
Sound energy as the device is released and the straw hits the top of the stick
Motion energy - as the elastic band pushes the toy upwards
Gravitational energy - as the toy is up in the air
Motion energy - as the toy falls back down

For chains of forces discussion:
Draw on the board the toy with step-by-step forces.
Our fingers hold the toy (with the force of friction) - a push
We push the toy down on the desk with a downwards force
The elastic band stretches - a pull - as we push down
When we let go the elastic band pulls
The straw moves upwards and pushes against the top of the toy
This pushes the whole toy into the air
Gravity eventually pulls the toy back down