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Challenge Variation: Calculating Current

In the Physics Level 1 Laboratory Workbook, Chapter 7’s experiment allows students to observe and record the effects of insulators and resistors on electrical current and the heat produced by the current. The experiment actually demonstrates “Ohm’s Law” even though the text does not refer to it that way. This variation is called a Challenge Variation, because students can use their original experiment and the formula for Ohm’s Law to uncover new information.

I. Prepare the lab notebook
Have students record the formula for Ohm’s Law (V=IR) in their notebook. They will want to write that V is the voltage, I is the current, and R is the resistance (resistance is measured in units called ohms).

II. Calculating the Current
Students could not measure the current in their Wookbook experiment, because they did not have their system hooked up to an amp meter. Can they still determine the current that flowed?

Using the equation V=IR, it is possible. Another way to write this equation is I=V/R (current equals voltage divided by resistance). The formula shows that when resistance goes up, the current goes down (I is inversely proportional to R).

So students can estimate the value of the current (I) by using the known value of the resistors (R) and the known value of the 1.5V battery (V).

III. What should the formula yield?
The students’ formula should look like this:
I (unknown current) = V (1.5V) divided by R (known ohms of the resistors used)

Feel free to write to us with information about how the experiment variations and expansions are received by your students. We appreciate all feedback.


Electrical Energy: Charging the Electroscope

The Chapter 6 Laboratory Workbook experiment for Physics Level I guides students through the process of building a simple electroscope and testing a few materials to create an electric charge. Let’s continue to make use of the fascinating little machine and allow students to learn more about which materials create the most charge.

I. Prepare the lab notebook
Students will want to create a quick table listing new materials to be tested and a space to record what happens to the strips of aluminum in the electroscope as each new material is tested. Was there enough data in the results of their first experiments for them to make more detailed hypotheses about each new category of material to be tested? Can they make a hypothesis about whether all materials in the same category will produce similar results?

II. Static electricity from various materials
Have students gather or locate a few samples of materials in categories such as cloth (cotton, wool, polyester or nylon), metal (copper, iron, or steel), or paper and plastic (plastic wrap, paper towels, gift wrap tissue paper, facial tissues). Students may also wish to vary the “rod” that is used to rub various materials in an effort to produce electricity. For example, if a plastic comb had been used, students may want to record the results of using that comb with these new materials and then repeat those experiments using a metal or plastic measuring spoon. Are results different when the “rod” is changed?

III. What happened?
Discuss with students their observations about which materials created the strongest separation of the aluminum strips and which made the least. Remind students that an object (the rod) is being charged because electrons are being moved from the source material.

Feel free to write to us with information about how the experiment variations and expansions are received by your students. We appreciate all feedback.


Chemical Energy of Atoms in Motion

Physics Level I Chapter 5 teaches students about the chemical energy released in a chemical reaction, that is, the energy of atoms and molecules. The voltaic battery experiment in Chapter 5 allows students to learn about the chemical energy of electrons. Let’s take this further with an experiment that allows them to observe the chemical energy of atoms in motion.

I. Prepare the lab notebook and materials
Have students read this experiment variation in full and create new Objectives and Hypotheses about how the size of the balloon may vary (or not) depending on temperature. They will need a small chart or Notes area to record any changes in size and a place to write their Conclusions.

The materials needed are a few balloons, a permanent marker, and a soft tape measure.

II. Molecules in Motion
Blow up a balloon and tie it off tightly. Explain to students that the air blown inside the balloon is actually a lot of molecules bouncing all around. The energy of motion from those molecules is what applies pressure inside of the balloon to keep the sides of the balloon expanded. What will happen if those molecules are slowed down? Decreasing the temperature of the air inside the balloon will slow the energy motion. (This process of cooling is actually converting thermal energy to potential energy.)

Once the balloon is blown up, carefully and lightly mark a line around the fullest part. It is okay for this to be approximate, as the line simply allows students to measure the balloon at the same place at differing temperatures. Measure the circumference of the newly inflated balloon and record the size. Place the balloon in the freezer. Students will want to take the balloon out after several minutes and quickly measure at the line. Record the new circumference. Place the balloon back in the freezer and allow it to remain there for a longer period of time before measuring again. The sides of the balloon will collapse, so if measuring is too difficult simply have students record their observations.

Now, let the balloon stay at room temperature again. Observe and, if possible, measure what happens as potential energy is converted back to thermal energy.

III. What happened?
Discuss with students how cooling – or slowing down the thermal energy of the molecules – changed the size of the balloon. Re-warming the air within the balloon increases the motion of the molecules, which increases the pressure inside the balloon. The increased motion once again changes the balloon size. Have students write a conclusion from their data and/or observations.

Feel free to write to us with information about how the experiment variations and expansions are received by your students. We appreciate all feedback.


Friction and the Transfer of Momentum

In Chapter 4 of Physics Level I, students learn about three properties of motion: inertia, friction and momentum. The experiment in Chapter 4 allows students to observe the transfer of momentum from marbles of varying sizes traveling at varying speeds to other stationary marbles. The experiment demonstrates the conservation of momentum. To expand the experiment, students can also observe the relative effects of two extremes of friction.

I. Prepare the lab notebook and materials
Have students read this experiment variation in full and create new Objectives and Hypotheses. The various marbles will already be labeled and weighed, as recorded in the Results chart A they completed previously. They will want to label new sections in their notebook to record what they observe in this expanded experiment.

II. Observing the effects of friction
Variation #1: Have students freeze a long pan of water. Once frozen, mark the center with a small line scratched on the ice to the side or use a piece of tape to the side of the rolling surface so that the center marking does not interfere with the “track” of the marbles. Using the solid ice surface, conduct similar exercises of rolling various sizes of marbles at various speeds to impact a stationary marble in the center. Have students record their observations about each combination of mass and momentum. Discuss how the smoother surface produces less friction, and how less friction changes the way momentum is transferred.

Variation #2: Have students set up a measured area in which to roll the marbles on a section of carpet. They may designate the “center” by placing a pencil or temporary piece of tape to the side of the “center” so as not to block the roll-way of the marbles. Repeat the combinations of marble sizes and speeds being rolled to impact a stationary marble. Discuss how the texture of the carpet increases the friction that works on the marble’s momentum.

III. What happened?
What happened when the amount of friction changed? Students will have recorded what they observed for each size and speed combination on each surface. Ask them to read their experiment Results and make valid conclusions about the relative amounts of momentum conserved when differing amounts of friction are at work.

Feel free to write to us with information about how the experiment variations and expansions are received by your students. We appreciate all feedback.


The Spit Wad Experiment

Chapter 3 of Physics Level I explores how work gets done when potential energy is converted into kinetic energy. The Chapter 3 experiment uses banana slices to test the relationship of mass and speed to kinetic energy. For a variation, students can use spit wads to demonstrate how increased potential energy converts to more kinetic energy. You will need these materials:

A new (or good condition) rubber band
Paper for a spit wad (or other small, soft projectile such as a small marshmallow)
A ruler
A long tape measure or a ball of string

I. Prepare the lab notebook
The experiment Objective students create will have to do with learning how increasing “strain” or “mechanical” potential energy (by pulling back the rubber band) affects the amount of kinetic energy released as work. Students should make a chart to record how far the spit wad travels when the rubber band is pulled back one inch, when it is pulled back two inches, and when it is pulled back three inches. Help them plot these numbers on a graph by marking the inches the rubber band is pulled back on the horizontal axis and the number of inches the spit wad travels on the vertical axis.

II. Safety and conducting the new experiment
This experiment is an excellent time to discuss or review safe practices for laboratory experiments, because mistakes or unpredictable outcomes could happen. It is preferable to use a new rubber band to decrease the chance of the bank breaking and snapping back on a hand. Likewise, students should be careful not to pull the bank back so far as to risk breaking it. Safety goggles should be worn. The spit wads should never be pointed at person, and especially not toward someone’s eyes.

Have one student hold down the ruler on a flat surface, such as a table, with the “0” end at the direction of the spit wad shot – or temporarily secure the ruler to a table. The “shooter” should position the rubber band at the “0” end of the ruler. Place the spit wad in the rubber band and pull the band back one inch before releasing it. Students then measure how far the wad traveled from the end of the ruler. Repeat the procedure, but this time pull the rubber band back twice as far. Record how far this spit wad traveled. Continue to shoot and measure for additional “strain” (how far back the band is pulled) within the distances that are safe from breaking the rubber band. Students should then plot the results on a graph.

III. What happened?
Pre-Level I students should be able to describe the relationship of increasing strain energy to work produced (travel distance of the spit wad). That is, the spit wad traveled approximately twice as far when the rubber band was pulled back twice as far. Level I and Level II students should be able to observe, measure and record more precise measurements. Students should write valid conclusions about the results achieved.

Feel free to write to us with information about how the experiment variations and expansions are received by your students. We appreciate all feedback.