Chapter 7: Machines, Work, and Energy
In the 7.2 screen cast, Mrs. Morales came upon a confusing slide. The publisher's slide actually has WRONG information in the table! Below is an edited version of the slide along with my corrected version of the table. The mechanical advantage of a rope and pulley system is equal to the number of sections of rope supporting the load.
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Mechanical Advantage and Friction
This video has a fun explanation of mechanical advantage. Near the end it also introduces the idea that friction will decrease the amount of work a machine can do. Our textbook chooses to wait until Section 7.3 to consider the effects of friction on simple machines. For all our calculations prior to 7.3, we are assuming the machines are perfect (that there is no friction, and output work equals input work). |
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How Do Pulleys Work?
This is another explanation of pulleys. They are using pulleys to lift fairly heavy objects. How to Make a Simple Pulley System
If you don't have true pulleys, you can still devise a system of ropes and carabiners with the same mechanical advantage. Impress your parents or siblings! (Get creative but don't put nails in anything without parental permission.) |
Chapter 9: Matter and Energy
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Expansion and Contraction
This video explains why gases expand and contract when temperature changes. It's generally a good explanation, but they show gas molecules changing direction randomly, which is not accurate. A gas molecule will continue in the same direction until it collides with another gas molecule or an object, such as the side of its container. How Hot Can It Get?
This video is just for fun and is not necessary to your understanding of our class content. However, it tries to answer a great question! |
Chapter 10: The Atom
If you want to know more about any element on the periodic table, check out this clickable periodic table from Thomas Jefferson National Accelerator Facility in Virginia!
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Chapter 12: Electric Circuits
Mrs. Morales misspoke in the 12.1 video when she talked about reflex arcs. One reason the reflex is so fast is that the signal does not go to the brain. It only goes to the spinal cord, which sends the electrical signal to your muscles. Here's a detailed explanation.
Ohm's Law mathematically shows the relationships between voltage, current, and resistance. Voltage is measured in volts, current is measured in amperes (amps), and resistance is measured in ohms. The units can be related by using the same equation.
The ampere is one of the base units of the SI-system. For those who are curious, Khan Academy explains the meaning of the ampere as well as other units related to electricity. Volts and ohms can be expressed in terms of kilograms, meters, seconds, and amperes as shown below.
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