Lesson: Sink or Float

We are now beginning our unit on density and buoyancy and I like to use this learning activity to introduce density. Making students aware of their misconceptions is one of the most powerful methods in teaching science. When you demonstrate the actual reality of the concept it can break their misconception and students are forced to change their thinking. I give the students the following challenge statement (word document):

“Ojbects that are high in mass sink in water.”

Students have to write a paragraph stating if they agree, disagree, or are somewhat in between with the statement. They have to explain in detail their reasoning. It is not important that they are actually right or not, they just need to be able to clarify their thinking. I then do the following (see video below).

Afterward the students need to explain in a paragraph if their thinking has changed and if so, they need to explain how. The items that were used in the demo can be found at Educational Innovations. Here is a list of the items, with their masses and densities (excel spreadsheet).

Lesson: Egg Saver

The egg drop is a staple of science classes. I love the egg drop. It is one of the few learning activities where all students can construct an apparatus that doesn’t require a parent to take over the student’s work, doesn’t require expensive or hard to get materials, and hey you might get to see eggs break! I like to do my version of the egg drop at the end of the year when middle school students are getting a major case of spring fever. I call my version of the egg drop, the Egg Saver project. I introduce the project by showing the students the video tittled Understanding Car Crashes: Its Basic Physics. The video, made by the Insurance Institute for Highway Safety, is hosted by a high school physics teacher and demonstrates how inertia, momentum, and impulse are essential in designing safe cars. We next go over the project parameters. The parameters are designed so that students must construct a container in which an egg can be quickly inserted and then extracted after a drop. Also no liquids or packing material are allowed. These rules are implemented so that students design a container that that has to conform to real life requirement like a car. Passengers need to be able to get into and out of a car quickly and passengers in a car are surrounded by liquids. I ban packaging materials so that students are a little more challenged. The size requirement is because I want it to be more car size than tractor trailer size, and it also forces students to be a little more creative. I then give the students the handout (word document) to the project. The project has 5 parts:

Part 1: Preliminary Design & Materials List
Students brainstorm and write a brief description of what their egg saver container would look like and how it would work. They also must write a list of materials that they might use. The purpose of this part is to get them started, which is the hardest part. They do this in class so that I know they have something written down.

Part 2: Final Design Specifications
Students have to draw a detailed diagram of their final container that shows the parts, dimensions, and the functions of the parts.

Part 3: Data Collection & Analysis
Students collect data on the mass of the egg and container, height dropped, time from release to impact, velocity, and momentum.

Part 4: Graph of Data
Students construct a line graph that shows momentum versus height.

Part 5: Final Analysis & Conclusion
Students write a paragraph that discusses the results of the experiment.

For an incentive to design a container that works, if a student’s container is successful at the highest height, 14 feet, the student is exempt from doing part 4 and 5.

We do the drops in the classroom with a 10 foot ladder. My classroom has a high ceiling which can accommodate the tall ladder. Watch a video of design that works.

Video Demo: Lava Lamp

A while back I posted an item from Steve Spangler’s Science site that demonstrated how to make lava lamps. I decided to go ahead and try it and I filmed it. The materials that are required for the demo are shown below. As the video shows the peanut butter jar is filled with 3/4 vegetable oil and 1/4 colored water. Place an 1/8 of an Alka-Seltzer tablet into the jar. The Alka-Seltzer reacts with the water to form carbon dioxide gas bubbles. The gas is less dense than the water or oil. The carbon dioxide gas bubble attach themselves to the colored water, causing them to rise to the surface. When the gas breaks through to the surface the higher density colored water droplets sink back down into the jar. The second part of the video shows the same demonstration, this time in a large test tube.

Handboiler

Educational Innovations’ website teachersource.com sells tons of unique science related items. One of those items is the handboiler. When you wrap your hand around the base the colored liquid (probably alcohol) heats up and moves up to the top where it eventually bubbles. My guess is that the molecules of the liquid speed up causing them to move up. When you let go the liquid eventually cools and goes back down via gravity. You can make the liquid go down faster by grabbing the top with your hand. I do this demo with student volunteers. We make observations and they hypothesize what is causing it. We also record who is able to send the liquid up the fastest.

Precautions: Don’t squeeze the handboiler. It can break easily.

Video Demo: Flame Tests

Every chemical has its unique characteristic properties. These properties can include hardness, density, melting point, boiling point, color, taste, texture etc. No matter what sample you have of a pure substance they will display its characteristic properties. This is how a an unknown chemical can be identified. The properties of the unknown chemical can be compared to the properties of known chemicals. In this activity there are 3 unknown chemicals (X, Y, and Z) that are to be identified based on 5 properties: color, boiling point, melting point, density, and color when burned. This is a simple and quick lab activity. The handout has the density, boiling point, and melting point filled in already. The students must observe the color and the color when burned–a flame test. Slide 1 shows the materials needed for the activity (the 3 chemicals are copper sulfate, strontium chloride, and lithium chloride). Slide 2 shows the Bunsen burner flame with the typical blue color. Slide 3 shows the inoculating loop collecting some of chemical Y. When the different chemicals are put in the flame, they burn at different colors (Slide 4 shows copper sulfate’s green flame, and slide 5 shows lithium chloride’s red flame).

Tips: Make sure students are careful to not contaminate the tubes and to thoroughly clean loop before testing each chemical.

Safety: Make sure students wear goggles, and know how to properly use a Bunsen burner safely.

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This is a variation on the flame test lab. Instead of using a Bunsen burner, a denatured alcohol flame is used (the best results is achieved by using methanol). Put a spoonful of strontium chloride into a Pyrex petri dish (this glass can take the heat, any other non Pyrex glass will break). Put about 2-3 spoonfuls of denatured alcohol into the dish. Swirl around to mix. Carefully light the alcohol on fire. You will probably need to swirl it so that the strontium chloride will burn and produce the red flame (lower left image). Try this with other salts and compounds that are safe to burn and will give color (like copper sulfate–lower right image).

Precautions: ONLY TEACHER DEMO! Be sure to use only Pyrex petri dish. The dish will get very hot! Don’t let water hit it right away. Be sure to blow flame out.