Polymers: Glue + Liquid Starch

I've been playing with around with recipes to make assorted slimes and such in preparation for a library program this summer.

A simple slime to concoct uses glue and liquid starch (you can find it in the laundry aisle)

You can find people using all different proportions, but I use about equal amounts of each (I eyeball it) poured into a cup.  You can add food coloring to the mixture as you desire.  Stir until things gel up (if it's too sticky, add more starch).  Then you can knead it with your hands.  (You can rinse off any extra starch).  As you play with it, it will become more smooth and gel/putty like.

You might also want to try using clear glue , with or without food coloring for a different effect.

How Do I Solve for m?

Since we were on the subject of manipulating equations this week, I thought I'd share this other tidbit with you...

I've had plenty of students who could recite F=ma and could readily solve for F, given m and a.  But, given F and a, they lacked the understanding of how to solve for m. 

This little trick solved a lot of problems (and even students capable of solving for m enjoyed using this). 

Draw a triangle and divide the triangle into three parts by drawing a T in it (see below).

Now fill in the variables.  In the case of F=ma, the F goes on the top and m and a each go in a bottom section.

To use....
Use your finger to cover the variable you're solving for an "read" off the equation. 

If you're solving for F, cover the F and you'll notice the m and a are next to each other, which means they need to be multiplied to get F.

If you're solving for m, cover the m and you'll notice that you're left with F over a, so you'll need to divide F by a get get m.

And finally, if you're solving for a, cover the a and you'll notice that you're left with F over m, so you'll need to divide F by m to get a. 


Much like the popsicle stick, this trick can work for any three variable equation like density and speed. 

As long as you can remember one iteration of the formula, you can recreate the triangle!

Manipulating Equations

In an ideal middle school classroom, all students would understand how to manipulate simple equations and be able to explain what happens to one variable when another is changed.  But, the reality of the classroom often means doing what you can to help some struggling math students work their way through equations in science class.  For those students, these simple manipulatives may just provide the crutch they need. 

This idea for these popsicle stick manipulatives, to help your students better understand what happens to the different variables in a formula, came from the Bond with James blog, and I found it through Pinterest. 

In its original form, this manipulative is used to help students better understand the ideal gas law.

But, since I never did a whole lot of instruction on the gas laws, I immediately began thinking of the equations I did use with my students that fit this pattern (i.e. three variables). 

The equations that came to mind were:
Newton's second law: F=ma
Density = mass / volume
Speed = distance / time

The manipulative is simple a popsicle stick,  labeled with m (mass), F (force) and a (acceleration).  The biggest trick is get the right letters in the right spots. 

Once the stick is set up, you can put it to work.  For our first scenario, lets say we want to know what happens to an objects acceleration if we decrease its mass, but keep the force constant. 

Because you're keeping the force constant, you'll place a finger over the F.  The stick now pivots around that point. 

Move the m end of the stick downward, to indicate a decreasing mass and observe the a end of the stick rising. 

Therefore, when the force is kept constant while the mass decreases, acceleration will increase. 

For another example....
What happens to the acceleration of an object when we keep the mass constant, but apply less force to the object?

Place your finger over the m, because mass remains constant.  Move the F downward to indicate a lessened force and observe that a also moves downward.

Therefore, when an object maintains a constant mass, but a decreasing force is applied, the acceleration will decrease. 

Here's a manipulative stick for the density equation:

It's used in the same way....
What happens to the density of an object if its mass remains constant but it's volume increases?

Place your finger over the mass, raise the volume end of the stick and observe the density end. 

If an objects volume increases without changing the mass, the objects density will decrease.      And while I don't have a picture of one.... a stick for the speed equation would have distance in the middle and speed and time on either end.      Hopefully with enough practice, your students will begin to internalize these ideas.  And when that happens, they will have a much better understanding of whether or not their answers make sense. 

Conservation of Matter: Steel Wool & Vinegar

This is another versatile demonstration to use in your student of chemistry - learn about chemical changes, chemical reactions, conservation of matter and even air pressure.

Depending upon the take-home message you want your students to get, you might structure the activity in a few different ways, but the basics are the same.

You'll need some steel wool, vinegar, bottles or flasks and a balloon.

Pull apart some strands of steel wool and push some into each bottle.  Pour some vinegar onto the steel wool.  (Some instructions tell you to soak the steel wool in the vinegar for a few minutes and then remove the steel wool.  I just left mine in it).

Stretch a balloon over the opening of one bottle, but leave the other as is.

You could find the mass of each system at this point, if you're interested in conservation of matter.

Allow the bottles to sit and the reaction to occur. 

The vinegar removes the coating from the steel wool, and the steel will be begin to oxidize in the presence of oxygen. 

As the reaction is occurring, the balloon will be pushed into the bottle.  Why?

The oxidation reaction is using up the oxygen in the bottle, which will lesson the number of air molecules in the bottle, thus reducing the pressure in the bottle.  Because the pressure outside the bottle is greater than the pressure inside the bottle, it will push the balloon in. 

You can stop there if you're interested in simply looking for evidence of a chemical change, studying the chemical reaction or seeing the affects of air pressure. 

If you're interested in conservation of matter, continue on. 

Find the mass of each system once again.

The closed system (i.e. the one with the balloon covering the opening), should have the same mass it had in the beginning. 

The open system's mass should have gained mass, as it continued to pull more oxygen into the system to carry out the reaction further. 

Compound Story

Have your students write some "science fiction".  

Each student chooses a compound (see below for some ideas) about which to write a story.  While not a report, the story should include scientific information about the compound and include the compound's empirical and structural formulas. 

Encourage your students to be creative in their writing and get into character - they could tell the story from the compound's point of view.  They could "be" one of the elements within the compound.  They could be reporting on a big news story involving the compound. 


If students are having a hard time getting started, they may want to look up their compound to find out what it's used for and where it's found - what they learn may be the start of a story. 

To make sure students don't get too carried away with the fiction aspect and forget the science part, you might wish to require them to use 12 (or whatever number you deem suitable) science terms.  Some possibilities:

• metal
• nonmetal
• solid
• liquid
• gas 
• chemical change
• physical change
• compound
• mixture
• periodic table
• family(ies)
• atomic number
• atomic mass
• stable
• unstable
• positive
• negative
• neutral
• valence electrons
• valence number
• empirical formula
• structural formula
• subscripts
• octet rule
• arms
• giver
• taker
• bonds
• share
• scientific name
• react
• reaction
• atom
• molecule

A list of compounds, to get you started:

• methane
• ethane
• propane
• butane
• octane
• acetylene
• benzene
• toluene
• carbon tetrachloride
• methanol
• ethanol
• propanol
• butanol
• carbon monoxide
• carbon dioxide
• calcium bicarbonate
• calcium oxide
• hydrochloric acid
• carbonic acid
• nitric acid
• water
• hydrogen peroxide
• hydrogen sulfide
• sulfuric acid
• ammonia
• nitric oxide
• nitrous oxide
• sodium chloride
• sodium nitrate
• sodium bicarbonate
• sodium hydroxide
• ozone
• silicon dioxide
• fructose
• sucrose
• potassium chloride
• citric acid
• vitamin C
• silver fluoride
• sodium fluoride
• silver chloride

Rate of Reaction: How Does Surface Area Affect the Rate of Reaction?

 The combination of Alka-Seltzer and water produce a chemical reaction.

To see how surface area affects the rate at which this reaction takes place, you'll need two Alka-Seltzer tablets and two glasses of water. 

 Keep one of the tablets intact and crush the other tablet (crushing it into an actual powder would be even better than the pieces I've shown here - good chance to break out the mortar and pestle if you've got them).

Drop the whole tablet and the crushed tablet into the water (each tablet into its own glass of water) and observe the length of time it takes each reaction to finish. 

Newton's 3rd Law: Popping Canisters

 This activity can be done as one activity in a series of stations on Newton's 3rd law, or it could be done as a demonstration if performed on an overhead projector* (does anyone still have those in their classrooms?!?!)

You'll need 2 film canisters (another relic), Alka-Seltzer, water and a pan with a line drawn down the center. 

I took the set-up picture with the transparent canisters, but later switched to the black**

Fill both canisters about half full with water.  You'll want to have the same amount in each canister.  

Cap one of the canisters and lay it on its side so the cap is against the line in the pan. 

For the next portion, you'll need to work quickly....
Add about 1/4 - 1/2 of an Alka-Seltzer tablet to the second canister and cap it.  Then lay that canister so its cap is against the line in the pan. (The two caps should abut one another). 

When the Alka-Seltzer creates enough gas to fill the canister, it will pop the top off.  At the same time it will push the second canister.  Equal force will be applied to each canister, but in opposite directions.  After the explosion, the two canisters will end up in mirrored positions.  

*If you want to do it on an overhead projector, draw a line down the center of a transparency using a permanent marker.  And use a minimal amount of water.  

**This is definitely a demonstration to play around with before you plan to do it in front of your students!  I've done it successfully several times in the past without problems, yet when I went to photograph it, I ran into problem after problem.  The first canisters I grabbed to use leaked so that enough pressure never built up to pop the top off.  Then I used too large a piece of Alka-Seltzer and sent the canister flying out of the pan and off the table (fortunately it didn't go through the brand-new dining room window!).  It's a great little activity, just give yourself a chance to practice it in advance! 

Dandelion Curls

It's spring in the northeast and that means (at least in my yard): Dandelions!

Did you know you can use dandelion stems to teach a simple (and pretty fun) lesson in osmosis as well as introducing the terms hydrophilic and hydrophobic?

Separate the stem from the flower and pull the stem into long strings.

Drop the strings into a tub of water and watch the stems curl up into all kinds of fun shapes! 

 If you drop the stem pieces one at a time, you can actually watch the curling process take place within just a minute or two.  Or you can dump a whole bunch in and have fun sorting through the results!

 What's happening?

The inside of the stem is hydrophilic, which is sometimes referred to as water-loving.  It's the part of the plant that absorbs the water.  And when it's placed into a tub of water, there's a whole lot of water to absorb!  The water moves into the cells through the process of osmosis. 

The outside of the stem is hydrophobic - it repels water.

The cells that make up the inside of the stem absorb so much water that they swell up.  The cells on the outside of the stem stay the same size.  The increasing size of the cells on the one side of the stem forces the stem into curls of various shapes.  

There's definitely something fun about sitting outside on a warm day and watching the curls form!  And if you can't be outside, grab some dandelions on your way to school and bring a bit of the outdoors in for your students.   

PS The idea of one side expanding more than the other side is similar to the way a bimetallic strip in a thermostat works.  The expansion is caused by temperature instead of water movement and it isn't as drastic as this, but it's conceptually similar. 

Purple, Green and Yellow: Marker Solubility

Purple, Green and Yellow by Robert Munsch

Brigid is a little girl in want of colouring markers, her mom isn't so sure.  Eventually Brigid convinces her mom to buy her some washable markers.  After a successful run with those, Brigid convinces her mom to buy her some scented markers.  And eventually, Brigid convinces her mom to buy her some super-indellible-never-come-off-till-you're-dead-and-maybe-even-later colouring markers. 

Brigid quickly learns about water soluble and water insoluble and your students can too.  In fact, your students can do Brigid one better and learn what makes those super-indellible-never-come-off-till-you're-dead-and-maybe-even-later colouring markers come off.

Place a paper towel over a short length of PVC pipe (or a small plastic container). 

Hold it in place with a rubber band. 

Students begin by using a water-soluble marker to make a circle on a paper towel. 

They then use a dropper to place drops of water in the center of the circle and observe.

Repeat this process using a permanent marker and water.

Finally, complete the process one more time using permanent marker and drops of rubbing alcohol. 

If time and budgets allow, students can create the Pinwheel t-shirts using the same process on shirts instead of paper towels. 

Snowflake Bentley: Sparkly Snowflakes

While both the book and activity have been featured on the Science Matters blog previously (here and here, respectively), it's been awhile and it's such a great pairing that it bears being part of this month's Picture Book Science.

Snowflake Bentley is a beautiful non-fiction picture book outlining the life of Wilson Bentley, the first man to photograph individual snowflakes. 

The highlights of Bentley's life are written as a child-friendly story.  Greater detail is provided in the margins of each page. 



This is a fun, artsy-craftsy project in which students can learn about solubility, super-saturated solutions and crystal shapes.  

Make a super-saturated solution of Borax and water:
--Fill a jar with hot water (boiling is best).
--Add Borax, a little at a time, until no more will dissolve (you'll know you're there because instead of dissolving the Borax will settle to the bottom)

Use pipe cleaners and thread to make a snowflake.

Attach a piece of thread to the snowflake.

Place the snowflake in the Borax solution and leave for several hours or overnight. 

In the morning, you'll have a beautiful, sparkling snowflake, covered with large crystals. 

If you'd rather not make snowflake shapes, you can shape the pipe cleaner into stars or other shapes.  You could also just place a straight pipe cleaner into the solution.

The pipe cleaner works well because all the fuzz on it gives the crystals nice places to attach, and thus works much better than just a string.  (Which may explain why all my attempts at making rock candy as a kid were met with utter failure (and a sticky mess)).


Safety Note: The Borax and the finished snowflake should come nowhere near the mouth.