Electrostatics

It is possible to charge a balloon to several thousand volts using electrostatics, for example, by
rubbing it on one’s hair or on different types of clothing. Does this mean that the balloon is also
storing several Joules of energy? Why or why not?
?Only a small amount of the energy used in an incandescent light bulb (regular bulbs commonly
used in households) is actually converted into light. What happens to the rest of the energy? How
more efficient light bulbs (LEDs for example) are able to waste less energy?

Discussion 2
In Discussion Forum 2, post your response to the following discussion questions

?Your company’s main competitor has built an extremely efficient transformer and is trying to market
it saying that the new transformer is able to step up energy. Do you agree with their statement?
What would you say?
?Power transmission lines generally operate and high voltage and low current. Discuss the reason
for this choice.
?If visible light and radio waves are both examples of electromagnetic waves, why can’t we see
radio waves?
?Why spy cameras in satellites and high-altitude aircraft are designed with large apertures
Discussion 3
In Discussion Forum 3, post your response to the following discussion questions

?Air in a cylinder is compressed to one-tenth of its original volume without change in temperature.
What happens to its pressure? Imagine now that a valve is opened in order to restore the initial
pressure value. What percentage of the molecules have escaped?
?Consider a 40,000 km steel pipe in the shape of a ring that fits snuggly all around the
circumference of the Earth. We are heating now the ring so its temperature increased by 1 degree
C. Now, the pipe will no longer be snug. How high the ring will now stand above ground level?
(Make as many simplifications as necessary). Data: Coefficient of linear expansion for steel is
11*10-6 /degree C. This means, for example, that a 1-meter bar of steel that increases its
temperature by 1 degree C will expand 11*10-6 meters (11 micrometers)
?Farmers resort to spraying fruit trees with water before a frost to protect the fruit from freezing.
Using the concepts learned in this module, discuss why this does or does not work.
?An electric fan not only does not decrease the temperature of the air, but it actually increases air
temperature. How can you then explain that you are cooled by a fan on a hot day?

Discussion 4
In Discussion Forum 4, post your response to the following discussion questions.

?Helium and lithium are two elements that differ only in one electron. Why do you think they exhibit
such different chemical and physical behavior?
?Why is food irradiated with gamma rays from a Cobalt-60 source? Does the food become
radioactive? Discuss your answer.
?Is carbon dating more appropriate to measure the age of materials that are a few years old, or a
few thousand years old or a few million years old?

Discussion 2

Discussion 1
In Discussion Forum 1, post your response to the following discussion questions

?Consider a plane that flies due east on a trip, and then returns due west following the same exact
route. Imagine also that there are no winds in each trip. Flying due east, the plane flies with the
rotation of the Earth, while flying due west, it flies against the rotation. Will the flight times be the
same? Different? Why?
?The velocity of an object falling in free fall increases with time. Does the acceleration also
increase? Why or why not?
?Why is that a cat that accidentally falls from a 50-story building hits a safety net below with the
same speed as if it fell from a 20-story building?
?What is the acceleration at the top of a jump?

Discussion 2
In Discussion Forum 2, post your response to the following discussion topic.

?A 5-kg fish swallows an absentminded 1-kg fish swimming towards it at a velocity that brings both
fish to a halt immediately after lunch. What is the velocity of the smaller fish before it becomes
lunch?
?Use the concepts of this chapter to describe what would happen if you fire a gun that has bullet ten
times as massive as the gun.
?An apple falls from a tree and strikes the ground without bouncing. What happens to its
momentum? Is momentum conserved?
?You and your friend toss a ball back and forth in the middle aisle of an airplane in flight. Does the
kinetic energy of the ball depend on the speed of the airplane?

Discussion 3
In Discussion Forum 3, post your response to the following discussion questions.

?One of your friends says that astronauts in orbit are weightless because they are beyond the pull
of Earth’s gravity. Do you agree with your friend?
?An astronaut lands on a planet that has the same mass at the Earth but twice the diameter. How
would the weight of the astronaut differ from the weight on Earth?
?If a piece of an airplane suddenly becomes detached during flight, it will crash to Earth. Would it
happen the same to a piece of satellite in orbit?
?When a satellite is placed into a higher orbit, what happens to its period?

Discussion 4
In Discussion Forum 4, post your response to the following discussion questions

?Imagine a superfast fish that is able to swim faster than the speed of sound in water. Would this
fish produce a “sonic boom”?
?Use the concepts from this module to explain why flying bees buzz.
?If the handle of a tuning fork were to be handled firmly against a table, would the sound from the
tuning fork change? If so, what would change?
?The strings of a harp have different length in order to produce different notes. However, given that
the strings in a guitar have all the same length, how are the different notes produced?