December 16th - Simple Machines

I was having so much fun teaching this topic that I forgot I had my camera and didn't take a single photo! :) We will be continuing this topic after the Winter Break so I'll try to remember to take some photos during that class session.

We started class with a quick introduction to the six simple machines: lever, inclined plane, wedge, screw, wheel-and-axle, and pulley. We talked about how all machines make life/work easier and that some need a power source to run while others, such as the simple machines, do not.

We completed the lab "Levers" to show just how one of the simple machines can help make things easier.
For this lab, the students were given a stack of four hardcover textbooks and were asked to try to lift the stack of books with their pinky finger. As you might imagine, they had a tough time with this! They were then given two pencils and instructed how to make a basic lever by placing one pencil on top of the other (in a + shape). The students then placed the pencils so the point of the top one was under the stack of books. They pressed down on the eraser end of the top pencil and saw how this lever was now able to lift the stack.

Levers - Rigid bars that pivot on a fulcrum (fixed point). In that first lab, the bottom pencil served as the fulcrum.

Levers are classified as either first-class, second-class, or third-class. Each class has a different fulcrum and load position. We spent some time discussing each lever and completed a short experiment for each one.

First-Class Levers - In a first-class lever, the fulcrum is located between the effort force and the load. To lift a load, a downward force must be applied to the opposite end of the lever. A seesaw is a good example of a first-class lever.
For this lab, the students were given a small cardboard crate, some marbles, a lever, a fulcrum, and a spring scale. We started out by placing the fulcrum far away from the load position (almost at the opposite end of the lever). The students then placed the crate of marbles (our load) on the end of the lever that was away from the fulcrum and the spring scale on the end near the fulcrum. The students then pulled down on the spring scale until the load began to move. They noted how much force (in ounces) was required to lift the load.
The students then repeated this lab after moving the fulcrum so it was located under the center of the lever. They noticed it took less effort to lift the load when the lever was in this position.

Second-Class Levers - These differ from First-Class Levers in the sense that the load is placed between the fulcrum and effort force. If you think of a wheelbarrow, the person pushing the machine (the effort force) is at one end, the load is in the middle, and the fulcrum is located near the front wheel.
For this lab, we taped the fulcrum to the edge of a desk then set up the lever by placing the fulcrum at one end of the lever bar. Our lever was hanging off the end of the table. We tied a string around the end that was hanging off and hung the marbles (in a drawstring bag) on the lever about 2 inches from the fulcrum. The spring scale was hooked onto the piece of string and the students pulled up on the spring, noting how much force was needed (in ounces) to lift the lever. We tried this again with the load (bag of marbles) 5 inches from the fulcrum and 8 inches from the fulcrum.

Third-Class Levers - In a third-class lever, the effort force is located between the load and the fulcrum. A fishing rod, with the effort force (reel) between the fulcrum (handle) and load (hook) is an example of a third-class lever. Tweezers are another example.
To demonstrate how third-class levers operate, the students taped the fulcrum to the underside of a desk (at the edge) with the point facing down. One student held the lever bar so one end was at the fulcrum. We tied a piece of string to the lever about 2 inches from the fulcrum and added the drawstring bag of marbles to the opposite end of the lever. The spring scale was then attached to the string. The students pulled on the scale and recorded the force needed to lift the load. We then repeated this with the scale placed at a distance of 5 inches from the fulcrum and again at 8 inches from the fulcrum.

Inclined Plane - An inclined plane is a smooth, flat surface tilted at an angle like a ramp. Instead of lifting a load straight up, an inclined plane allows a load to be moved over a longer distance to reach the same height. This requires less effort.

Inclined Plane lab - We used the lever bar from the previous labs to create our inclined plane or ramp for this experiment. The students used books to create an incline, starting with one book. The cardboard crate was filled with 40 coins to create a load. The students placed the load at the bottom of the ramp and used a piece of string to attach the spring scale to the load. They then pulled on the scale and measured the effort needed to pull the load to the top of the ramp. We repeated this lab using 2 and 3 books to create steeper inclines.

Wedge - A wedge is two inclined planes back-to-back. Wedges work by changing the direction and amount of force. Some examples of wedges include an ax, nails, a knife, and teeth!

Wedge lab - For this lab, the students used different materials to attempt to lift a crate of marbles. The students used the eraser end of a pencil, the point of a pencil, a crayon, and the pointy end of a pair of scissors to attempt to lift the crate of marbles. The students discussed which ones made the job easier. The pencil point and the scissors were found to be the best wedges.

Screw - A screw is an inclined plane wrapped around a cone or column.

"Lifter" lab - Each student was given a large wood screw. They placed two fingernails on the first ridge at the tip of the screw and then turned the head of the screw to observe its movement.
Screws are used to connect things but they can also be used to lift items. Screw jacks, for example, can lift houses or cars.

We had just enough time at the end of class to go back and complete some more labs on the simple machines we covered today.
"Ramp" lab - This lab showed how a winding mountain road is an inclined plane.
The students were each given a pencil, a ruler, a piece of paper, and some tape. They cut a 5-inch square from the piece of paper then drew a diagonal line across the square. The students cut across the line and colored the longest edge of one of the paper triangles. They then taped the triangle to the pencil so the shortest leg of their triangle was taped vertically to the pencil. The students then wound the paper onto the pencil and saw the colored line make a shape like a winding road or screw around the pencil.
As we discussed, inclined planes make work easier by gradually traveling upward over a long distance. A winding mountain road is a longer way up a mountain but it is easier than traveling straight up a side of a mountain.

"Weakling" lab - This lab demonstrated a second-class lever.
Each student was given a toothpick. They placed the toothpick across the back of their middle finger at the tip of their fingers and under the first and third fingers. The students then tried to break the toothpick by pressing down with the first and third fingers. We tried this again by moving the toothpick down to the first knuckle of the middle finger.
In this lab, the fingers were acting as a second-class lever similar to a nut-cracker. The fulcrum in this lever is where the fingers join the hand so more force is needed to break the toothpick when it if placed farther from the fulcrum.

The labs "Levers," "Ramp," "Lifter," and "Weakling" are from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

The labs "First-Class Lever," "Second-Class Lever," "Inclined Plane," and "Wedge" are from a Lakeshore Learning Science Activity Tub on Simple Machines.

**We will take two weeks off for Winter Break so there will be no class on December 23rd or 30th. Our last class for the Fall semester will be held on Thursday, January 6th. During that class we will finish up simple machines and see how simple machines can be combined to create compound machines.
Learning Center classes for the Spring 2011 semester will most likely begin during the week of February 21st. Check your e-mail in the new year for information about class offerings.

December 9 - Heat and Temperature (continued)

We continued our study of heat this week by learning more about the transfer of thermal energy. We also studied endothermic and exothermic reactions and conductivity of heat.

To begin class, I asked the students to name some sources of heat. These can include the sun, geothermal heat, and fuels such as wood, charcoal, coal, oil, gasoline, and natural gas. One of the first answers given by a student was friction which was a great segue into my next question: "Can friction be a source of heat?" :)

I asked the students what would happen if they pressed their hand against a cool tile wall or the cool metal cabinet in our classroom. They knew the cold object would make their hands cold. I told them that if they then moved their hand away and touched the same spot with their other hand, that the wall or cabinet would actually feel a little warmer. I then explained this happens due to the flow of heat from the students' warm hands to the cool wall or cabinet.

We then discussed how two drinks that were originally at very different temperatures could reach the same temperature over time. I asked the students to imagine they were working in a restaurant. Two customers had just left and you are cleaning up the table. One of the customers had a hot chocolate and the other had an ice-cold soda. When you picked up the drink containers, though, you noticed they are now the same temperature. How did this happen? The students realized the heat from the hot chocolate had transferred out to the cooler air while the warm air had transferred into the icy soda. Heat generally flows from a warm object to a cooler object.

Here's a fun lab to try at home (with minimal materials!)

"Heat - Energy Extraordinaire!"

Mix a dish soap and water solution in a cup (use 1/2 tsp. of liquid dish soap and 1 tbsp. of hot tap water).
Add hot water to a second cup so it's about half-full.
Lower the mouth of a plastic bottle into the detergent solution so you have a nice film that covers the mouth of the bottle (think of the film you want when dipping a bubble wand into bubble solution).
Now, slowly push the bottom of the plastic bottle into the cup of hot water.
Observe.
As we learned, heat energy likes to travel from warmer areas to cooler areas. When you push the plastic bottle into the cup, the heat from the water travels into the bottle. This warms up the air that is in the bottle causing the air molecules to get excited and move faster. This increases the air pressure causing it to create a bubble at the mouth of the bottle. 

We switched gears at this point to learn about conductivity. Conduction is a point-by-point process of heat transfer. What that really means is that if one part of an object (say, the bowl of a metal spoon) is heated by direct conduct (or contact) with a heat source (say, a bowl of hot soup), the neighbouring parts of the object (in this case, the stem of the spoon) will also become heated. Heat travels along or through an object by conduction.
The molecules in any object, as we learned last week, are in constant motion. When one part of an object is heated up, the molecules start moving faster. This causes them to bounce off each other more and transfer heat as they bounce. Eventually, through bouncing and hitting and heating lots of other molecules, the temperature of the entire object increases. Through the process of conduction, all the molecules pass heat around to each other until they are all hot.

"Cold Foot" experiment:

For this lab, we placed a bathroom rug and a piece of aluminum foil on the floor and left them undisturbed for about 10 minutes (while we completed the next lab, "Heat Conductors"). Each student stood with one bare foot on the foil and the other bare foot on the rug. They then compared how their feet felt.
A good conductor of heat (the foil) will allow for the flow of heat. This happens due to those bouncing molecules passing heat around to each other. A poor conductor (also called an insulator) does not allow for this flow of heat. In fact, insulators work to keep the heat from escaping the warm object and transferring to a cooler object.
The aluminum foil felt colder than the carpet because, being a good conductor, it allowed for heat to flow from the students' warm feet. The carpet is a poor conductor so it kept the students' feet warm by trapping their heat in.

"Heat Conductors" experiment:
For this lab, each student was given three spoons: a metal spoon, a ceramic spoon, and a wooden spoon. I asked them which spoons they thought would make good conductors of heat and they gave their predictions. They were also each given a foam cup that was about half-full of very hot water. The students placed the three spoons in the hot water at the same time and let them sit for a few minutes. They then pulled the spoons out one-by-one and felt the temperature differences. The metal spoon was the clear winner/the best conductor. The ceramic spoon came in second since its stem was a little warmer but nowhere near as warm as the stem of the metal spoon. The wood spoon's stem did not heat up at all.
I then gave some examples of conductors and insulators. Metal, of course, is a great conductor of heat. I also pointed out that it is a good conductor of electricity which is why wires are metal. Plastics (such as the foam cup) and ceramics are often used as insulators since they are poor conductors. We talked about the use ceramics in cars (brake pads) and space shuttles to help protect engine parts from heat. I showed the students a pan with a copper bottom and asked why they thought the pan had that on the bottom. We also discussed whether it would be a good idea to stir hot soup on the stove with a metal spoon as well as a better alternative for this job.

To finish up the lesson, I taught the difference between endothermic and exothermic reactions. I wrote the two words on the board along with the words "thermal energy" and asked the class to point out the similarity. We talked about how "therm" relates to heat.
I then circled the prefix "endo" and explained that this means "inner" or "to draw into." We discussed the endoskeleton that humans and all other mammals have in common. I repeated this with the prefix "exo," explaining this one means "outer" or "to give off." We talked about the exoskeleton that ants have.
Endothermic reactions take in or absorb heat while exothermic reactions give off heat. A very simple example of an endothermic reaction is the process of ice changing from a solid to a liquid. In order for an ice cube to melt, it has to take in heat from its surroundings. It melts because thermal energy flows from a warmer object to the cold ice cube.
A basic exothermic reaction would be lighting a match. Striking a match causes the release of heat from the chemical on the match head into the air.

"Heat Changes" lab:

This lab demonstrated an exothermic reaction.
For this lab, I filled a baby food jar with water and then added a teaspoon of powdered bleach. I stirred the mixture and then inserting a thermometer. The students checked the thermometer every few minutes.
Because bleach contains oxygen, adding water to it creates a reaction that gives off oxygen gas. Heat is also a product of this reaction.

Next week: Simple Machines

The lab Heat - Energy Extraordinaire! is available as a PDF from the American Chemical Society (www.acs.org or www.acs.org/kids). A link to the PDF can be found on this website:
http://search.acs.org/search?q=Heat-Energy+Extraordinaire&client=acs_r2&output=xml_no_dtd&proxystylesheet=acs_r2&sort=date%3AD%3AL%3Ad1&entqr=3&oe=UTF-8&ie=UTF-8&ud=1&site=acs&x=0&y=0

The lab Heat Conductors was found on this website:
http://www.kids-science-experiments.com/heatconductors.html

Cold Foot is from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

Heat Changes is from Chemistry for Every Kid.
VanCleave, J. (1989). Chemistry for Every Kid: 101 Easy Experiments That Really Work. San Francisco: Jossey-Bass.

December 2 - Temperature and Heat

We started this week with a review of kinetic and potential energy as well as the law of conservation of energy. I then used a science kit to demonstrate some other energy changes.
Using a D-cell battery, a rubber band, some wire, a motor, and a propeller, I showed how chemical energy in the battery can be changed to electrical energy (through the wires). This then made the propeller spin which was a change to kinetic energy.
After this, I showed how the battery's chemical energy and the electrical energy from the wire could be changed to sound energy by connecting the battery and the wire to a buzzer.
Finally, I showed how chemical energy can be changed to heat (thermal) and light (radiant) energy. All we had to do here was light a candle.

The candle's thermal energy provided a nice segue into today's topic: Temperature and heat. I showed a transparency which had the three states of matter: solid, liquid, and gas, and how the particles in each of these states move. The students learned that solids have particles that are tightly packed together and are unable to move very quickly. Particles in liquids are a little more loosely packed so they can move around a bit more and are also able to move faster than those in solids. Gases have particles that are spaced far apart and move very quickly.
We used this to discuss kinetic energy. While we can't see the particles in a desk or a book move, they are constantly in motion! That desk or book, then, have kinetic energy. The faster those particles move, the more kinetic energy the object has.

Here's how kinetic energy relates to temperature. In science, temperature is the measure of the average kinetic energy of the particles in a sample of matter. Basically, as the particles in an object move faster, their kinetic energy becomes greater and the temperature of the object increases. I asked the students if they thought the particles in a mug of hot tea or those in a glass of iced tea moved faster.
The students were then asked if they thought temperature and heat are the same thing. Heat is the type of energy while temperature is the measure of that energy.

We moved on to complete a few experiments on temperature and heat.
"Hot Band" - This was a very simple lab but it demonstrated the concept. Each student was given a rubber band. They placed the rubber band against their forehead and described the temperature of the band. They then stretched the band and placed it back against their forehead and then told how it felt different. The students noticed that the stretched band felt warmer. When the students stretched the band (using mechanical energy), they caused the particles in the band to move farther apart. This increased the kinetic energy of those particles and allowed it to be transferred to heat or thermal energy.

"Smoke Rings" - This lab showed the downward flow of cold water through warmer water.
We used a bowl, a baby food jar, some food coloring, a piece of aluminum foil, cold water, and warm tap water. I filled the baby food jar with cold water and then added an ice cube to chill it further. The bowl was filled with warm water. We removed the ice cube from the baby food jar and added 7 drops of red food coloring. I then covered the jar with the foil, held it in place with a rubber band, and used a pencil to poke a hole in the foil. We turned the baby food jar over and placed it in the bowl so the top of the jar was just below the surface of the water. The students then took turns tapping the bottom of the jar.
The students observed the cold water from the baby food jar flowing down through the water in the bowl. When we looked really closely, we saw the cold water coming out of the baby food jar in spurts and then dispersing a little (it is supposed to look like rings, hence the name of the lab). The particles or molecules in the cold water are closer together than those in warm water so the cold water weighs slightly more. This makes the cold water sink to the bottom of the bowl of warm water.

"Puff Signals" - This experiment also involved hot and cold water. However, rather than showing cold water moving through warm water, this one showed hot moving through cold.
For this, we used two large-mouthed glass jars. We also needed more red food coloring, a baby food jar, aluminum foil, and 5 ice cubes. We placed the ice cubes in one of the large jars and then filled the jar with cold water. The baby food jar was filled with hot water and 7 drops of food coloring were added. Again, the baby food jar was covered with some foil that was held on with a rubber band. The baby food jar was then placed inside the empty large jar. I removed the ice cubes from the cold water in the other jar and then poured the water into the jar holding the baby food jar. We used a pencil to make a hole in the foil and then used the blunt end of the pencil to tap the foil.
The students saw the hot water puff up out of the baby food jar. As was explained earlier, the hot water is lighter (due to the spacing of its molecules) so it is able to rise to the top of the cold water.

We had a little help from my friends Ben and Jerry for this next experiment. :)
I asked the students what they thought would happen if they placed an ice-cold spoon on top of a scoop of ice cream. I then asked what they thought would happen if a hot spoon was placed on the scoop. What about two hot spoons?
I placed a metal spoon for each student into a baggie of ice to cool it off. One metal spoon for each student was left out at room temperature. A third spoon for each child was heated in steam coming from a kettle. The students tried the room temperature spoon first and noticed little difference (unfortunately our ice cream was already a little melty but they didn't see it melting any more from this spoon). They then tried the ice-cold spoon and discussed what they saw. Last came the hot spoon which, as they had predicted, caused quite a bit of extra melting!
I explained what happened while the students enjoyed their ice cream. The hot spoon caused the ice cream to melt due to a transfer of energy from the spoon to the ice cream. When I placed the spoon in the steam, this caused the particles of the spoon to start moving faster which increased the temperature of the spoon. This energy was then transferred from the hot spoon to the cold ice cream. Two spoons would cause more melting since they have twice as much mass. The more mass an object has at the same temperature, the more thermal energy it has.

We finished up by trying out another lab to demonstrate the transfer of thermal energy. We didn't have much success with this one so feel free to try it out at home!
"Magic Coin" - For this lab each student needed a glass soda bottle and a coin that was larger than the bottle's opening (we used quarters). They also used a bowl of cold water.
The students held the coins and bottle mouths in the cold water for a little while. After removing the objects from the water, they placed the coin on top of the bottle opening. The students then grabbed the bottle neck with both hands and held their hands in place for several seconds. The coin will "jump" (one student actually got it to work).

The warmth from the students' hands caused the air inside the bottle to warm up. As we learned, this caused the particles to move faster and expand. As the air expands, the coin has to move or jump to allow those air particles to move around freely.

Next week: Look forward to continuing our discussion of heat. We'll talk more about the flow of heat (build on what we saw in the ice cream experiment) and we'll also talk about exothermic and endothermic chemical reactions.

The "Magic Coin" lab came from this website:  
http://www.kids-science-experiments.com/magiccoin.html


The lab "Hot Band" is from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

The labs "Smoke Rings" and "Puff Signals" are from Chemistry for Every Kid.
VanCleave, J. (1989). Chemistry for Every Kid: 101 Easy Experiments That Really Work. San Francisco: Jossey-Bass.

November 18th - Kinetic & Potential Energy; The Law of Conservation of Energy

We started out this week discussing different types of energy. I asked the students to name any types of energy they could think of. They did a great job and named almost all the ones I had listed! We also talked about where energy can be found - everywhere.

Energy: The ability to do work or the ability to move something with a force.
We spent some time comparing the two categories of energy: kinetic (working energy) and potential (stored energy). We then moved on to a quick discussion of renewable and non-renewable energy sources.
To provide some examples of kinetic and potential energy, I used the image of a flowerpot sitting on a windowsill. If something, a cat for example, knocked the pot off the windowsill, gravity will cause it to fall toward the ground. As it falls, its potential energy changes to kinetic energy.
We each stretched rubber bands and discussed what type of energy the band will have if we were to let it go. Again, the energy changes from potential to kinetic if you let the rubber band go. The stored energy in the stretched rubber band, or any other stretched or compressed elastic object (a spring or bungee cord, for example), is known as elastic potential energy.
We placed a textbook on the edge of a classroom table and talked about the energy in the book when it is just sitting on the edge and the energy in it if we pushed it off the table. Since gravity will work on the book to push it to the ground, the stored energy in the book is known as gravitational potential energy.

"Loser" Lab - This lab determined the effect mass has on kinetic energy. We attached a string to the handle of a bucket and then taped the other end of the string to a table. A wooden block was placed on the floor in front of the bucket. A student pulled the bucket back and let it swing into the block. We observed how far the block moved. The students then added several large pieces of modeling clay to the bucket and repeated the exercise, again measuring how far the block moved.
Kinetic energy is increased as the mass of a moving object (in this case the bucket) is increased. This allowed the heavier bucket to push the block further than the empty bucket.

"Bump!" Lab - This lab showed the transfer of kinetic energy. Each student was given a textbook and 6 marbles. The students opened the book and placed 5 of their marbles in the book's center groove and pushed them close together. The students then positioned the last marble in the groove about an inch from the other marbles. They gave the marble a push to make it bump the others. The students noticed that the 6th marble stopped once it hit the first marble in the row. They also saw the last marble in the row move away from the group.
This happens due to a transfer of kinetic energy from the marble that was pushed to the first stationary marble which then transferred energy to the next marble, and so on. The last marble eventually receives this kinetic energy and is able to move forward as a result.

"Energy Change" Lab - This lab demonstrated the effect height has on the energy of a moving object. The students were each given a paper cup, a pencil, a ruler (one with a center groove), a pair of scissors, and a marble. The students cut a "door" in the paper cup and then placed the cup over one end of the ruler. They used the pencil to raise the other end of the ruler and then rolled the marble down the ruler. The students observed how far the cup moved after the marble hit it.
The students were then each given a textbook and replaced the pencil with the book. This raised the ruler a little higher. They repeated the experiment and discussed the results.
The students discovered the cup moved farther when the marble started from a higher point. Objects that are higher off the ground (or table, in our case) have higher potential energy than those closer to the ground. As we learned earlier in this lesson, when the object falls or rolls, the potential energy changes to kinetic energy. The height increase also served to increase the kinetic energy, allowing the marble to hit the cup with more force.

At this point in the lesson, we took a break from labs to discuss the law of conservation of energy. This law states that energy cannot be created or destroyed. The students learned today that energy can change; it is just always there in some form.

We completed two labs to demonstrate the law of conservation of energy.
"Bonk!" Lab - The students were given a ruler, a 2-foot piece of string, some tape, a book, and 2 small bouncy balls (equal size). One end of the ruler was placed inside the book. The students then tied the center of the string around the other end of the ruler. They used small pieces of tape to attach the two balls to the two hanging ends of string, making sure they were at the same length. The balls were then pulled away from each other and released.

The students saw the balls continue to hit and bounce off each other until they eventually stop moving. This is another lab showing the change from potential to kinetic energy. After the students used their energy to pull the balls away from each other, the balls had potential energy. When the balls were let go, this energy changed to kinetic energy. The balls will then change their kinetic energy to heat (thermal) and sound energy.

"Shifter" Lab - For this lab, each student used two classroom chairs, some string, and two washers. The students placed the chairs about 1 yard apart and tied a piece of string between them so they had a tight light between the chairs. They then cut two 24-inch pieces of string and tied a washer to the end of each piece. The free ends of these strings were tied to the string between the chairs. One of the strings with an attached washer (String A) was lifted and pulled away so it was level with the top of the chairs. The students then let their String A go and watched it swing back and forth. As this happened, they noticed String B start to move.
Again, this shows the transfer of energy from one object to another. The strings form a pendulum and the energy is constantly transferred back and forth between String A and String B until friction eventually causes them both to stop swinging.

The labs "Bonk!" "Loser," and "Energy Change" are from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

The labs "Bump!" and "Shifter" are from 200 Gooey, Slippery, Slimy, Weird, and Fun Experiments.
VanCleave, J. (1993). 200 Gooey, Slippery, Slimy, Weird, and Fun Experiments. New York: John Wiley and Sons, Inc.