Students need to be familiar with various terms and calculations that relate to electrical circuits. They should be able to define VOLT, AMP, conductor, switch, resistor, capacitor, fuse, circuit breaker, series and parallel circuits. They should be able to explain how a battery stores and releases energy.
Electrical circuit: manages the flow of electrons by shaping the conductor (often copper wire) and controlling the electrical field.
Volts: electrical potential
Lead acid batteries, common in cars, use an Oxidation/Reduction reacting to create electrical current. LEO the lion says GER. Loss if Electrons Oxidation, Gain of Electrons Reduction.
Resistance: how a conductor impedes the flow of electrons. Electrical heating devices use resistance in wires to create heat. For example, toaster, coffee maker, electric stove. There is resistance in all electric lines.
If resistors are in series the total resistance is the sum of the resistance in the resistors.
If the resistors are in parallel, the total resistance is 1/Rt=1/R1 + 1/R2 Therefore if two resisters (10 ohms ad 20 ohms) are in series the total resistance is 30 ohms. If they are in parallel, the total is 6.7 ohms. Go ahead and prove the math!
We demonstrated much of this with Snap Circuits. Each student was instructed to put together a number of circuits which used a switch, resistor ( and demonstrate to me the resistor worked ), rheostat ( a variable resistor ), sound device, light bulb, fan, etc. Also put together circuits which demonstrated how a series and parallel circuit worked. Each demonstration was then supported by a drawing in which the students had to use the correct symbol for the various electrical devices.
We discussed personal situations which demonstrated how fuses and circuit breakers worked in their houses. Older houses very often do not have enough power in their wiring that you can run your coffee machine and your toaster at the same time in the same room. You have to find an outlet on a different circuit to run the toaster if you have already started your coffee pot! Do not under any circumstances replace a fuse with a penny so that you can get more power to an appliance; good way to start a fire. There are various levels of power (amperage) in various circuits running in your house. Obviously it takes more power to run your kitchen than your bedroom. It takes more power to run your washing machine or your HVAC than your television, etc.
Thursday, April 11, 2019
Friday, April 5, 2019
Apologia Physics: Electrostatics
Electrostatics measure the instantaneous charge between two atoms. For examples see the pictures below. We rubbed balloons on our sweaters and on our hair to create static electricity. It is best to do this on a cold dry day so you may have to change the order of topics in your Physics instruction to get this demonstration done before Spring. Then we hung tape and yarn from rulers which extended beyond the edge of the table. The static electricity attracted the tape and yarn. We also applied tape to the table and ripped the tape off and hung it from a ruler. Repeat with another similar piece of tape and hang it close to the other one. They should repel because they have the same charge.
How is this static electricity created? You actually rip electrons off your hair or sweater when you rub with the balloon. Therefore the balloon takes on a negative charge. The tape rips electrons off the table and therefore the tape takes on a negative charge.
An atom has protons and neutrons in the nucleus. Electrons orbit the nucleus. To change the charge of an object you add or subtract electrons as we did above. The number of protons and neutrons does not change.
Apologia Physics: Current Topics for the study of Electricity
I struggle with anything concerning electricity and magnetism in my teaching of high school Physics. Maybe it is because most of the other topics in Physics I relate to the operation of a car! So I decided to veer away from the topics covered in our textbook and have the students do a small research project on topics that are relevant to current events. These projects would also serve to update my knowledge.
The topics below came from several sources. My wife and I helped judge a science fair for grades 6-8 at a local school in February. Several ideas came from projects done by those students. My students are also very interested in electric cars and of course all their electronic gadgets. I have eight students and we came up with eight topics. I have asked them to do some research, summarize their research into a one page paper including sources, present their findings to the class and lead a discussion of the topic with the class. Here are the topics.
How do very high and low temperatures impact the range of an electric car? How and why? Explain change in chemical and physical reactions.
What factors impact battery life in an electric car?
Compare operating costs over several years for three similarly sized cars: gas powered, electric powered and gas/electric hybrid.
What is an EDDY current? How is it created? What are its uses? Make a model.
How does a MAG LEV train work? Where are they in use?
How does a wireless charger work? Contact vs. Non-contact. See article by Joanna Stern in the Wall Street Journal May 5.
Compare various aspects of performance of a gasoline powered car vs. an electric car. Find comparable cars and/or cars in the same price range.
Compare the safety of a gas powered car vs. an electric car.
Projects are due after the Easter break. I will follow up at that time.
On Thursday April 11 I sent the students a summary of how to write a five paragraph essay. It is important to have an Introduction (containing your subject, hypothesis, scope, three main ideas), three paragraphs each discussing one of the main ideas, and a conclusion. The conclusion needs to be based on what was discussed in the preceding paragraphs.
The verbal presentation to the class should be based on notes or an outline. Do not read your essay and just refer to your notes if necessary. No one wants to listen to someone reading a Powerpoint presentation! I saw too much of this in my career in business.
The topics below came from several sources. My wife and I helped judge a science fair for grades 6-8 at a local school in February. Several ideas came from projects done by those students. My students are also very interested in electric cars and of course all their electronic gadgets. I have eight students and we came up with eight topics. I have asked them to do some research, summarize their research into a one page paper including sources, present their findings to the class and lead a discussion of the topic with the class. Here are the topics.
How do very high and low temperatures impact the range of an electric car? How and why? Explain change in chemical and physical reactions.
What factors impact battery life in an electric car?
Compare operating costs over several years for three similarly sized cars: gas powered, electric powered and gas/electric hybrid.
What is an EDDY current? How is it created? What are its uses? Make a model.
How does a MAG LEV train work? Where are they in use?
How does a wireless charger work? Contact vs. Non-contact. See article by Joanna Stern in the Wall Street Journal May 5.
Compare various aspects of performance of a gasoline powered car vs. an electric car. Find comparable cars and/or cars in the same price range.
Compare the safety of a gas powered car vs. an electric car.
Projects are due after the Easter break. I will follow up at that time.
On Thursday April 11 I sent the students a summary of how to write a five paragraph essay. It is important to have an Introduction (containing your subject, hypothesis, scope, three main ideas), three paragraphs each discussing one of the main ideas, and a conclusion. The conclusion needs to be based on what was discussed in the preceding paragraphs.
The verbal presentation to the class should be based on notes or an outline. Do not read your essay and just refer to your notes if necessary. No one wants to listen to someone reading a Powerpoint presentation! I saw too much of this in my career in business.
Tuesday, February 12, 2019
Egg toss lab
We are studying impulse force. Impulse is the force an object experiences when there is a change in momentum. The change in momentum equals the impulse force times the change in time. What time? The time elapsed as the object changes momentum.
An easy way to demonstrate this is to toss an egg back and forth between two students. How do you reduce the impulse force? Look at the equation in the first paragraph. If a student tosses the egg to another student, the change in momentum is equal to the mass of the egg times the speed at which the other student throws the egg. The catcher can either catch the egg with his hands fixed or he can swing his hands and arms back as he is catching the egg.
If you catch the egg and it stops very suddenly, it will probably crack. This is great fun the first time!
If the catcher swings his hands and arms back as he catches the egg the egg usually does not crack. The difference is much more evident if you catch the egg on a cookie sheet instead of your hands. You can also use a bedsheet.
The key concept to understand is that the momentum is a constant in each situation so if you want to reduce the impulse force you must increase the time it takes to bring the egg from its initial speed to a stop.
There are several great examples in real life such as crush zones designed into the front of a car's frame and body, airbags in your car, etc.
The opposite is also true. If you are hitting a baseball, you only have so much strength. If you want the ball to have more momentum so that it goes further, you have to increase the time the bat is in contact with the ball as you are hitting it. In many sports such as baseball, golf and basketball, this is called follow through.
Have fun with the lab.
An easy way to demonstrate this is to toss an egg back and forth between two students. How do you reduce the impulse force? Look at the equation in the first paragraph. If a student tosses the egg to another student, the change in momentum is equal to the mass of the egg times the speed at which the other student throws the egg. The catcher can either catch the egg with his hands fixed or he can swing his hands and arms back as he is catching the egg.
If you catch the egg and it stops very suddenly, it will probably crack. This is great fun the first time!
If the catcher swings his hands and arms back as he catches the egg the egg usually does not crack. The difference is much more evident if you catch the egg on a cookie sheet instead of your hands. You can also use a bedsheet.
The key concept to understand is that the momentum is a constant in each situation so if you want to reduce the impulse force you must increase the time it takes to bring the egg from its initial speed to a stop.
There are several great examples in real life such as crush zones designed into the front of a car's frame and body, airbags in your car, etc.
The opposite is also true. If you are hitting a baseball, you only have so much strength. If you want the ball to have more momentum so that it goes further, you have to increase the time the bat is in contact with the ball as you are hitting it. In many sports such as baseball, golf and basketball, this is called follow through.
Have fun with the lab.
class discipline
It seems as though some of the homeschool students I teach are not accustomed to deadlines and remembering to bring their completed work to class. They also have a long list of excuses when they have not finished their work such a: the printer broke, they stayed late at sports practice, they were tired, etc. They also insist on maintaining some practices that are not correct such as not using scientific notation and forgetting to include units of measurement.
So we came to a mutual agreement. Offending students would do pushups, just like in basic training for the military for each infraction. Did not finish a report? Ten pushups. Present a problem solution and not express the answer in scientific notation? Ten pushups. The parents I have spoken to about this are all supportive. The point I am trying to make is that when these students are in college, the military, or have a job, none of these behaviors are acceptable!
So we came to a mutual agreement. Offending students would do pushups, just like in basic training for the military for each infraction. Did not finish a report? Ten pushups. Present a problem solution and not express the answer in scientific notation? Ten pushups. The parents I have spoken to about this are all supportive. The point I am trying to make is that when these students are in college, the military, or have a job, none of these behaviors are acceptable!
The importance of being able to write well and appropriately to a scientific audience
The class has been writing their egg toss lab reports. It is important that they write well but also write appropriately to a scientific audience. In all writing it is important to use proper punctuation, grammar, and sentence structure. It is also important to write succinctly and concisely and not use trite phrases.
I have never been able to write prose and poetry so I will not comment on the differences between what the students may have learned about writing in their literature, composition, and history classes and what I am teaching them about writing. Hopefully those differences are not too great.
Examples of phrases and words I do not want to see in lab reports: honestly, actually, grab the …, who would have thought?, etc.
We also write lab reports in the third person, present tense, active voice, indicative mood.
For example: The student rolls the ball.
I have never been able to write prose and poetry so I will not comment on the differences between what the students may have learned about writing in their literature, composition, and history classes and what I am teaching them about writing. Hopefully those differences are not too great.
Examples of phrases and words I do not want to see in lab reports: honestly, actually, grab the …, who would have thought?, etc.
We also write lab reports in the third person, present tense, active voice, indicative mood.
For example: The student rolls the ball.
Saturday, January 19, 2019
Apologia Physics Module 9 Horsepower calculation lab
This module is about power. Power is force exhibited over time. Attached is a lab that will help you understand the stair climbing horsepower calculation. Please complete the lab using these instructions and bring to class Tuesday. Please make sure you have completed three trials that are reasonably similar in time. If you have results that say you only have a quarter horsepower or that you have three horsepower try again!
Here is the horsepower lab with stairs. This lab has calculations.
Here is the horsepower lab with stairs. This lab has calculations.
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