Science

Crazy Catapults – STEM Project with simple machines.

I love introducing STEM projects (like these catapults) to my 8th grade students. Because this is the third year I have taught most of the students, they know my rules, and I know their tendencies. By this time, I can foresee some problems that the students could run into and avoid them. I can also try new things with these students. They won’t have melt-downs if something doesn’t go as planned! I’m also continually impressed with how many cool ideas and designs they come up with… they are very creative!

These eighth graders recently wrapped up a unit on forces and simple machines. Last year, I saw a few lesson plans that involved building catapults and thought that would be a perfect way to tie everything together. The project went fine, but students didn’t quite use the simple machine concepts like I had hoped they would. So this year, I decided to amp up the catapult plan and make better! These eighth graders love a challenge and could roll with any minor surprises!

Lesson Overview

First, we discussed a little bit of catapults history. Together, we talked about the different types that were used for various reasons. Accuracy, power and distance are all important features of a quality catapult. Knowing this information, students received the challenge to design and build a catapult that would meet the three main criteria. Launching mini marshmallows as far as possible, trying to accurately shoot the marshmallows into a bucket, and using a sugar cube to knock down stacked cups were their tasks.

The catapults were a huge hit! The kids wanted to bring in materials from home to work on them (which I didn’t allow), and had unique ideas of how they wanted their catapults to work. I will say that next year, I will have to give a few more design restrictions. Some of the created designs had difficulty with one or two stations. Trebuchet type catapults seemed to work the best for the stations I choose.

Overall, I would say this year’s catapult project went much better than last year’s. I made sure students had to identify the simple machines in their design, and even calculate the mechanical advantage. Next year, I will adjust it more (aren’t we as teachers always tweaking our lessons–even the successful ones??) but I would say this project is a keeper!

Materials to use:

Popsicle sticks, spoons, rubber bands, various sizes of cups, tin cans, toothpicks, duct tape –really anything you can find that you think will work!

Other things you may need:

Cups to stack for the power station, sugar cubes (can be used for harder projectiles), meter sticks, a container for the accuracy station, and tape for starting lines. Use this worksheet packet as well – CrazyCatapults.docx. I adapted this from TryEngineering.org and from Vivify’s site. Both these sites contain great ideas for STEM challenges and activities and you should check them out!

Mystery Powder Investigation

Mystery time! Can you figure out what the four white substances are? This lesson can be used to show properties of difference substances or demonstrate differences between chemical and physical changes. Or it can just be for fun!

 

Lesson introduction:

I introduced this investigation to students after discussing chemical and physical properties of substances. For a “warm-up” I asked the students if they would ever accidentally mistake glue for milk. “Gross!” seemed to be the normal response. However, they easily listed several reasons – color, viscosity, density – it was clear which liquid students could drink. I even showed students what happens when you mix vinegar with both. Again, they were grossed out by the curdling milk.

Powder Investigation Set Up

Before class, I prepared the lab for the students. Containers A, B, C, D were filled with a different white powder. I also included a magnifying glass, beakers of water and vinegar and an eye dropper in their lab baskets. Sheets of foil were ready for them to use as “plates” or testing stations for their powders as well. I do use iodine, because this makes a chemical reaction with one of the powders, but I don’t let any of the students handle it. and we put any iodine mixture in separate spaces.

Materials used

I placed cornstarch in container A, salt in container B, baking soda in container C and sugar in container D. Feel free to use other white substances (safe ones please!), but I chose these four because I had them available in my classroom, and they are “safe” to use. Remember… middle schoolers want to eat everything. I’m not going to use things that might put them in danger! Each substance also has a unique reaction to at least one of the tests that students can choose from. Cornstarch changes the color of iodine, salt has crystal-like particles, baking soda fizzes with vinegar, and sugar tastes sweet!

Time to test!

Students test a powder by mixing vinegar and watching for changes that occur!

I let students choose which tests they would like to do with the substances. This includes mixing the substances with water, vinegar, or iodine, feeling the textures of each, using the magnifying glasses to observe the particles, and of course, the taste test (but I make them wait to do this last so it is not a giveaway!)

It is important to emphasize where students may see chemical changes happening. I ask the students these questions:

Are there bubbles?

Was there a color change?

Did something new form?

Can you get the substances back?

While testing, students fill out a chart like this: MysteryPowders. A “P” is placed in the blank if a physical change occurs and a “C” for any chemical changes.

Mystery Solved!

At the end of the time, I do tell the students what each of the substances were and they are excited whenever they guessed correctly!

Have fun investigating!

 

Density Rainbow – Using Colored Liquids to Explore Density

 

Density can be a tricky topic to teach. Students usually understand the concept of mass. They can feel the difference in something that is more massive (or heavy) than something else. Volume can be shown easily — which one is bigger? What takes up more space? When you put mass and volume together, sometimes students get mixed up. Does heavy always mean dense? Does little mean it will be less dense?

I have a fun activity that addresses some of these possible misconceptions. It uses simple materials and the results turn out beautifully (if students do the lab correctly!).

The set up:

This activity can be used before introducing density as an inquiry activity, or it can be used as a culminating activity. Since my sixth grade students have worked with density here and there, I incorporate the lab after our official density lesson. In the days before, we work on understanding what makes something dense, students practice calculating density and we may even play a few rounds of “Sink or Float.” (This is SO easy for any grade level and students love it! You can either do it as a demonstration, or have small groups do it. Just get a beaker filled with water and random items from the classroom and students must predict whether it will sink or float when dropped in the water!)

Density Rainbow

In the Density Rainbow activity, students find the density of five different liquids and pour them one at a time into a 100mL graduated cylinder. If the students are careful with their pouring, the result is a beautifully layered, colorful cylinder!

Before measuring a liquid, students predict where in the layer it will go. On the top? Bottom? Somewhere in the middle? Because I want to include the math, I make students find the mass and volume (about 15mL) of each liquid, and then calculate the density. Most students see the connection between the numbers they are getting and where the liquid will end up. The higher the density, the lower it will go in the cylinder.

Make sure you tell the students to pour each new liquid carefully! Tilt each cylinder and pour the liquid down the side of the 100mL cylinder SLOWLY! This is especially important with the rubbing alcohol. If students splash, the colors will get mixed and the final result won’t be as pretty.

Here are the liquids I use:

The liquids ready to go!
  • A) Water with green food coloring
  • B) Vegetable oil (no food coloring necessary – it won’t mix well anyway!)
  • C) Blue dish soap (you can use any color of dish soap you would like, but I like the blue best!
  • D) Corn syrup with purple food coloring (this gets very thick and sticky!
  • E) Rubbing alcohol with red food coloring.
I label all the cups so students know what liquid to use when.

Condiment cups are also extremely helpful in this activity. I can prep this lab the day before, pop the lids on all the liquids and not worry about spilling or evaporating. You can find the cups most grocery store in the paper goods aisle. If you have a Gordon Foods nearby, they have huge packs of them too!

The final product!

If you would like to use the handout that I do, here it is: Densityrainbow.doc

Notes and extensions:

Because I have students find the mass, they must first find the mass of the empty graduated cylinder they use to measure with. I am always double checking that they are subtracting the mass of the empty cylinder from the mass of the liquid plus the cylinder. If they don’t do this, their calculated density will be off!

Another extension I do is have the students change the volume and predict if the layers will still be the same. If we used 30 mL of vegetable oil and only 10 mL of water, what will happen? We do this as a group and it leads to the discussion of why adding MORE liquid does not change the density. A few of my quicker students pick up on the fact that when you increase volume, you are also increasing mass, so the density will be the same!

Have fun adding some color to your classroom! If you have any other ways you like to teach density, share them! I love introducing new activities to my classroom repertoire!

Gummy Bear Osmosis


I love working with food whenever I can in my science classroom. And I especially like using candy. You pull out a single M&M, and all eyes are on you. When you tell them they will be using any type of candy to do a lab experiment, they can’t wait to get started. Obviously, the first question I get is “Can we eat this?” Now, I’ve taught middle school students awhile now so I am extremely aware of the fact that even if I say “No,” students will still sneak in a lick or nibble! I’ve learned to keep a few extra samples of whatever food I’m using so at the end of class, students can get their candy fix!

In my seventh grade class, we have been discussing cells and how materials move in and out of the cell membrane through passive transport. This leads to discussing the concepts of diffusion and osmosis. When I found a lab that used candy to demonstrate the concept of osmosis, I knew it was a winner! I have been using a lab I found on this blog which is site that has many other resources and great ideas for teaching science. The link to the pdf file which I have used and adapted from year to year is linked below.

Day One

The lab must be done in two days. First, students will take a gummy bear and measure the height, width and mass. Next, the gummy bear is placed in a beaker of distilled water overnight. It’s always amusing to hear the predictions of what will happen. Without fail, I get at least one prediction of “It’s gonna explode!” What is it with science class and students’ expectations of exploding objects??

Students use electronic scales to find mass
I love using the triple-beam balance and so do the students!
Day Two

The students come in super excited to check out their bear the next day. Of course, half the groups have named their little gelatin blobs and are thrilled/mortified to see that their gummy babies grew overnight! Students check the height, mass and width again and find the percent change. (Always love the math tie in!) A graph is made and written responses are required. Then at least one student in every group tries to slurp down the bear or the water left behind. Disgusting, but amusing. (And don’t worry, I do not promote this, but it’s not worth fighting. I just make sure the beakers are clean and safe!)

While groups are working, I try to connect with them to see why they think the gummy bear grew to the size it did. Most students have no issue seeing the connection to osmosis! (Let’s be honest… there are always one or two that still remain oblivious to the fact that we science teachers DO have reasons for activities we choose to do in the classroom!) Other questions that can be used to dig deeper are:

“If we left the gummy bear in the beaker another night, would it continue to grow even bigger?”
“What might happen if the bear was left in salt water?”
“How might we make this process faster or slower?”

If you were to do a little google search on Gummy Bear Osmosis you can find many ideas and variations of how this may work in your classroom! This is the lab I’ve used and I encourage you to use it and check out the science blog here too! Thanks to “Mr. Poach” for creating this awesome lab packet! Happy diffusing!!