Phys 1210 Conceptual Physics
Child's Question-of-the-Day Part 3

Weeks 10-15 Waves & Sound, Electricity & Magnetism, Light & Color

"What makes sound loud?"
The greater the back and forth distance the source of the sound moves (ex: tuning fork; speaker membrane), the louder we will perceive the sound.
The greater the distance a vibrating object moves back and forth, the stronger the air nearby will be hit and compressed.*  A vibrating source's back and forth motion produces compressions and expansions in the air nearby, resulting in a longitudinal wave. As this longitudinal waves compressions and expansions come in contact with your eardrum, your eardrum will correspondingly move back and forth. (just like what happens when you pat on a drum). The greater the compression, the harder the air will "hit" your eardrum and the louder the sound will be. [Note: there are more effects that contribute to the loudness of the sound, effects related to our perception of sound.]
(* when the object moves back an expansion, or rarefaction, will be produced in the air).

"How does that paper cup telephone work?"
Vibrations causing vibrations causing vibrations...
Your vibrating larynx caused the air about your mouth to vibrate, the vibrating air hit the paper cup (at this point the sound emery becomes mechanical energy), causing the cup to shake/ vibrate, the vibrating cup (connected to the string) caused the string to vibrate, this vibration traveled down the string (just like a wave on a rope) and caused the second cup to vibrate, which caused the air inside that cup to vibrate (now the mechanical energy is converted back into sound energy), which caused your friend's eardrum to vibrate and now he/she can hear what you had to say. One important thing to keep in mind: keep the string between the two cups taut!

"Why does sound travel faster in water or in railroad tracks than in air?"
The sound travels through air, water, and tracks using the particles in that material. The vibrating source his the particles about it, causing those particles to vibrate. The closer the vibrating particles, the sooner they bump into each other, the quicker the energy of the sound wave (thus the sound wave itself!) is passed on.

"Do sound waves travel on forever?"
A sound waves will travel on forever if the energy of the sound wave does not change form (i.e., to another form of energy). A sound wave is made when a vibrating source hits the particles of the medium surrounding it, giving these particles motion/ kinetic energy. Any individual particle in the medium passes on its kinetic energy when it collides with the next particle. However, as these waves travel outward, the colliding particles might not pass on all of their newly acquired kinetic energy, but keep some of it in the form of its own "internal" vibrational &/or rotational energy. We call this heat, or thermal, energy.
[Teacher Note: The energy of a sound wave is not "lost" just because the wave is further from its source. As the sound waves travel out from their source, these waves do spread out 3-dimensionally; their amplitudes decrease, and their energy is spread out over a larger area. Sound decrease in intensity the further you are from the source of the sound. But the total energy of the sound wave will not have changed unless the energy is lost to the particles of the medium as discussed above.]

"Is there sound on the moon? If an astronaut on the Moon dropped a hammer, would there be sound?
How do the astronauts communicate with each other ?"
No, there is no sound on the moon. Because of the Moon's weak gravitational field, the moon does not have an atmosphere, therefore it has no air. Sound requires a medium to travel.  The source of sound is a vibrating object. When an object vibrates, it disturbs the air near it, and this in turn creates sound waves traveling away from the source of the vibration. Since there is no air on the moon, an vibrating object has no matter particles to disturb, therefore a sound wave cannot be produced. But you might want to note that when the hammer hit the ground, it caused the ground to shake a bit, which would send out a sound wave (kind of like a very small earthquake). His fellow astronaut might feel this vibration, but he would have to put his ear to the ground to hear this sound wave.

"How do the astronauts speak to each other (and mission control) on the Moon?"
Radio waves. Sound waves can travel inside the astronauts' helmets where there is a medium (his or her breathing air!) When the astronauts speak, the sound waves can not travel out of their helmets out into the empty space/ vacuum around the moon. But within the helmet, these sound waves are "picked up" by the microphone and converted into radio waves. See chapter 9. (The astronauts have helmets containing air for the purpose of breathing!)  The radio waves are then transmitted to the other fellow. Radio waves (electromagnetic waves) need no medium to travel. They can travel through empty space.

"While out in space, is it possible for an astronaut to hear a star (or a starship!) explode?"
No, in "outer space" there is no air. If there is no air (or any other matter) between the astronaut and the exploding spaceship, then there will be nothing for sound to travel through. [So: did Bruce Willis really hear the asteroid blow up?! While standing on the asteroid, could he have felt the vibrations of the exploding asteroid?]

"How does my  (charged) balloon stick to the wall?"
The negative charge on your balloon is making the wall's surface positively charged, and then these unlike charges attract.
How did the wall become positively charged? The wall has atoms and all atoms have negative charges (electrons) and positive charges (protons). The positive protons are deep inside the atom in the nucleus; the negative electrons surround this nucleus. When a negatively charged balloon comes up to the wall, the negative electrons in the wall's surface atoms are repelled (like charges repel). The electrons are pushed to a degree to the "back side" of the atom. That will leave the "front side" (the surface of the wall) mainly positively charge (due to the protons). Now the charges that are closest to each o
ther (wall's protons and balloon's electrons) will attract each other. Walla - the balloon will now "stick" to the wall.

"How does my (charged) balloon bend the water stream?"
Water molecules naturally have a negative side (the oxygen) and a positive side (the hydrogens) This is because of how the oxygen and hydrogens share electrons. Water molecules are called "dipole molecules."  The negative charge on your balloon is attracting the molecule's positive side, and repelling the water molecule's negative side. This causes the water molecule to turn about so that its positive side (the hydrogens) faces the negative balloon. Now the balloon will attract the stream of water. This animation  that illustrates this force: http://www.colorado.edu/physics/2000/applets/h2ob.html (uses an electron and a water molecule)

"What is the tingling irritation that I feel when I touch my tongue to the ends of a 9V battery"?
You are feeling electric charge move across your tongue.
The terminals of the battery are the connections to the electrical potential energy stored within the 9V battery. When you touch both terminals with your wet tongue, you are providing a complete path for the charges to move from one terminal to the other. Your wet tongue is a great conductor of electricity. When you touch your tongue to both of these terminals, you have set up a path for the electric charges to easily flow through.

"Does the wall switch give the light its electricity"?
No, the wall switch does not give the light its electricity, it only controls the flow of electricity/ electric charge. This flow of electric charge needs a continuous path/ circuit. When you turn the lights off, the wall switch breaks this path (or "opens" the path). We say that the switch is "open." When you turn the lights on, you are "closing" the path, you are connecting the path for the charge to flow through. The switch is "closed".
The source of the electricity (what provides the electrical energy) is the electric power plant's generators. The power plant gives us electricity, it provides the voltage needed to push the charge around the paths/ circuits. This charge flows through the filament of the light bulb, the filament uses this moving energy to produce light energy.

"Why do all the Christmas light go out when I remove one of the bulbs"?
The bulbs are essentially wired is series, remove one bulb from the circuit (this will 'open' the circuit) and all the other bulbs go out. Why don't all the bulbs go out when that one  bulb burns out (i.e. its filament breaks "open")? Within each bulb is a tiny parallel circuit. If the filament breaks, there is an alternate path for the current to flow through.

"What is a short circuit?"
An electric circuit is a path where electron's can flow out from the voltage source, all the way around through an electric appliance (or light?) and back again. A short circuit occurs when the wires in the circuit totally bypass the appliance. The electron's will then have a path that they can flow through without going through the appliance. Not only will there be no electron flow/ current flow to the appliance, there will also be no resistance to the current that is flowing. The current flow will be very great and the wires could melt down and a fire could start.

"How do magnets lift objects?"
A magnet can lift an object by making that object a magnet!
Magnets can only lift certain objects. (What kind of objects can be lifted by a magnet?) These objects are made of the same kind of material that magnets are made out of. Let's consider a paper clip. The paper clip has within it regions that are magnetized. The paper clip as a whole is not a magnet, because these small magnetized regions are not all lined up together, with their north poles all pointing in one direction and their south poles all pointing in the other. When a magnet comes near the paper clip, the pole of the magnet closest to the paper clip will attract the opposite pole of the magnetized regions within the paper clip. These regions within the paper clip will line up together and the paper clip will become a  magnet temporarily. The two magnets (the permanent one and the temporary paper clip one) will be attracted to each other and stick together and you can then lift up the paper clip with the magnet.

A paper clip "sticks" to the north pole of my magnet. If I turn the magnet around will the paper clip still be attracted to the magnet? Or will the south pole of my magnet repel the paper clip?
(Teacher Note: It is best to just give the student a magnet and pile of paper clips and let him/ her try it out!)

"How does this magnet pick up this long chain of paper clips?”
A magnet can lift a paper clip by making that paper clip into a (temporary) magnet! And in turn, that newly created “paper clip magnet” can lift up another paper clip! Magnets attract materials that are ferromagnetic (for example, iron). Let's consider a paper clip. The paper clip has within it tiny microscopic areas that are already magnetized. These areas are like tiny magnets (called magnetic domains) each with their own north and south poles. The paper clip as a whole is not a magnet, because these tiny south-north pole areas are all jumbled up. When the south pole of the magnet comes near the paper clip, it will attract all of the north poles of the small magnetic domains within the paper clip (and vice versa). These domains within the paper clip will now be lined up together and the paper clip will become a magnet (but only temporarily). The two magnets (the permanent one and the temporary paper clip magnet) will be attracted to each other and “stick” together and you can then lift up the paper clip with the magnet. The magnetism of the paper clip in turn aligns the magnetic areas within the next paper clip, attracting opposite poles one to another. The two “stick” to one another, and paper clip by paper clip, this process causes a chain of paper clips to hang down from the original magnet.

"When I break this magnet in half, will its magnetism be gone?”
When I break this magnet, will its magnetism be gone?
No! The magnet is magnetized throughout its whole body. Break the magnet in half and you will have two smaller magnets. If you were able to look deep within the magnet, all the way down to the microscopic atomic level, you would find groups of atoms that are magnetized. These groups (called magnetic domains) are like tiny magnets each with their own north pole and south pole. In a material that can be magnetized, ex: paper clip the magnetic domains are all jumbled up. But the domains within a magnet are lined up together, with all the north poles in one direction (attracted to the south poles) and the south poles in the other direction (attracted to the north poles). These domains start at one end and go all the way through the magnet to the other end. [Picture/ diagram?] You can break the magnet in half and each half will still have its tiny magnetic domains, all lined up and pointing in the same direction. You will now have two magnets.
[Teacher Note: In the process of breaking the magnet, the domains directly by the broken edges can be distorted a bit due to the stress while breaking the magnet.]

"How does water power turn into electricity?" (or "What is hydroelectric power?")
[First qualify with child as to what water power is.]
An electric power plant uses water power to generate electricity. These power plants use the moving energy of steam (from boiling water) or the moving energy of falling water (from dams or waterfalls). The moving water pushes against the blades of an electric generator's turbines. The turbines turn the wires within the generator electromagnet. Because of the relative motion of the wires and the electromagnet, the electromagnet exerts a force on the electrons in the wires. This force makes the electrons move through the wire. Now you have electricity flowing.
[There are different ways to get the water boiling. One method is to burn coal or oil, another is to use the energy of a nuclear reaction to heat and boil the water.]

"What is an electromagnet?"
An electromagnet is a device that "makes" magnetism from electricity flowing through a wire. To make an simple electromagnet strong enough to pick up heavy (magnetic) materials, you need to design the electromagnet in the following manner. Wrap an insulated wire many times around an iron core (for example: a large nail or a screwdriver). Attach the ends of the wire to a battery. The greater the voltage source, the greater the current. The thicker the wire, the greater the current. The greater the number of coils, the greater the magnetic field. Watch out though: if the current is too great, the electromagnet can get very hot!

"Why does the sun shine in the daytime and the moon at night?"
Daytime is the time when it is light/ bright outside, and the sun has to be in the sky in order for there to be a lot of light about. Our part of the Earth is facing the sun, when we have daytime. the other part of the Earth is facing away from the sun, they can not see the sun, and they have nighttime. They are actually in the shadow of the Earth! As the earth turns about, we move into the shadow of the Earth and the sun looks like it is setting. It is now nighttime for us. Nighttime is dark, because there is no sun in our part of the sky.
When we see the moon shining, it is not making its own light like the sun does, but it is reflecting sunlight to the Earth. It is easy to see the moon "shining" at night, because the sky is so dark, which makes the moon appear to be very bright. The moon can also be seen during the daytime, but you have to look carefully over the sky to find it. Because the sky is so bright with sunlight, it is harder to find the moon during the daytime than it is during the nighttime.
[Teacher Note: the subject of the phases of the Moon could easily come up at this point!]

"What makes a shadow get longer or shorter?"

"To see my feet in the mirror, do I need a larger mirror, or can I just step back from my mirror?"
If you can not see your feet in the mirror when you are close up to the mirror, you will not be able to see them when you step away from the mirror. A larger mirror will not help you! If you can see your feet when you step away from the mirror, try stepping forward a bit and with each step, look carefully into the mirror, as far down as you can and you will be able to still see your feet. In order to see you full image, you need a mirror about half of your height.
[Note: I am assuming a vertical mirror and a flat horizontal floor. Also, if there is a cabinet or dresser in front of the mirror, this might block your view of your feet. It will be in your "line-of-sight", so to speak.]

"Is fluorescent light better than regular light?"
Fluorescent light uses less electricity than regular, incandescent light bulbs. Therefore it is cheaper. However, fluorescent light does not produce all possible light waves that make up white light. It looks like white light, but not all of the colors that make up white light (visible light) are in it. As a result, some shades of red, or green, or blue, etc., will look different under  fluorescent light than under an incandescent light.

"Why is the sky blue?"
The sun produces white light, which is actually a combination of all of the colors. It is the blue and violet wavelengths of sunlight that are scattered the most by the molecules in our atmosphere. Thus when we look up in any direction in a clear sky, we see light coming to us from the molecules scattering about this blue light.
What happens to the rest of the sunlight? It passes straight on through the atmosphere, though some of it may be scattered out by dust or other larger molecules. Water droplets in clouds scatter about all of the different colors/ wavelengths, thus clouds tend to look white.

What does the moon's sky look like? On the moon there is no atmosphere, therefore no air molecules at all to scatter light about. No light is coming from the different parts of the "sky", except for the part of the sky with the Sun and the distant stars. As a result, the astronauts standing on the moon saw a black sky surrounding the sun and stars.

"What is a rainbow made of?"
A rainbow is made from sunlight passing in and back out of water droplets in the sky. These water droplets act like tiny little round prisms, separating the white sunlight into all of its colors. The sunlight is bent/ refracted as it enters into the water droplet, bounces/ reflects of the back of the water droplet and passes back out of the front of the droplet. Each color from each droplet will now has its own path. We see red light coming from the droplets at the top of the rainbow and violet light coming from the droplets at the bottom of the rainbow. And in between those droplets, all of the other colors are also being separated out (from the white light) by other droplets.

Have you ever heard of a moonbow? That's a rainbow made from moonlight - The best time to see one is when the moon is full, don't forget to "turn your back to the moon"! http://wug.physics.uiuc.edu/courses/phys150/spring02/slides/chap23/sld009.htm (In this image the sky looks blue and the grass green, like they do during the daytime. It may be hard to believe that this picture was taken at night. The photographer had to expose the film for a "long" period of time (30 sec.) in order to "catch enough" the moonbow light. At the same time he or she caught a lot of scattered moon light from the sky and grass, etc.

It depends on the kind and the amount of radiation that your body is exposed to.
Radiation is made up of electromagnetic waves. There are lots of different kinds of radiation: visible light, ultraviolet light, heat radiation/ infrared light, microwaves, radio waves, X-rays, gamma rays. (Each of these electromagnetic waves have different frequencies.)
Visible light is great to see things by, but too much light can hurt our eyes. (Never look directly at the Sun!)
from a bonfire feels great on a cold day, but too much can burn your skin.
Ultraviolet (UV) light helps our bodies' cells form Vitamin D, but too much will burn/ tan our skin and cause premature aging of our skin and for some people skin cancer. (UV photon frequencies can trigger chemical reactions.) We can enjoy and our bodies can tolerate visible light from the sun all day long, but not the ultraviolet light from the sun.
X-rays help a doctor find a broken bone or a tooth cavity - but too much can damage cells in our body.  Dentists do not like to take more than two annual X-rays of your teeth (and each time they do, they stand behind a heavy wall to protect themselves from those X-rays).
Gamma radiation can be used to kill cancer cells, but they can also kill healthy cells.

"What is the difference between 'good' ozone (which protects the Earth from UV radiation) and 'bad' ozone (in smog)?"
'Good' ozone and 'bad' ozone are chemically the same thing (both are the same molecule, O3, made up of 3 oxygen atoms). Ozone is highly (chemically) reactive and what makes one 'good' and the other 'bad' is their location.
We live (and breath!) in the bottommost part of our atmosphere (the troposphere). Ozone in this part of the atmosphere (due to pollution) could chemically react with our respiratory/ lung cells, causing respiratory problems.
Above the troposphere is the stratosphere, within which there is the "Ozone layer" (~20 kilometers above our heads). This layer of our atmosphere blocks ultraviolet (UV) light. The chemical reaction cycle O3 (ozone) <=> O2 (oxygen) absorbs some of the sun's UV radiation (and emits IR radiation).

"What makes this "glow-in-the-dark" lizard/ frog glow after I turn out the lights?"
When then light was on, the atoms and or molecules within the frog were "storing up" the light energy. These are special atoms/ molecules that have the ability to absorb light energy, and release this energy later (in the form of light). It doesn't release the light all at once, but bit by bit, until all of the "stored energy" is gone. This process is called phosphorescence.

"What makes neon colors so bright?"
These neon or fluorescent colors look bright because they are absorbing high energy packets of light (ultraviolet light) and releasing that light in the form lower energy packets (visible light). The ultraviolet light is not visible to our eyes, but this "newly produced" light is. So it looks like that bright green sign is producing its own light. Instead, it is the fluorescent atoms in the sign that are changing invisible light into visible light.

"Does 'Nuke it in the microwave' mean that there is a nuclear reaction going on in the microwave?"
No, there is no nuclear reaction taking place inside of your microwave! Microwave ovens produce microwave radiation. This electromagnetic radiation is absorbed by molecules of water (& fat!). When these molecules absorb this energy, they start to move more. They have more heat energy. This absorption process changed the electromagnetic energy into heat energy. These changes took place between atoms and molecules. No change occurs in the nucleus. No nuclear reactions will take place!

"What makes seasons and why do we have four of them?"
When our part of the Earth is directly facing the Sun for most of the day, we have summer. You probably have noted how the Sun is up high in the sky on summer days. In the winter time, the Sun is low in the sky. Our part of the Earth, during wintertime, is not facing the Sun directly, and less of the Sun's energy is able to reach us. Thus in the winter it is colder. What is happening in order for this change to take place? The Earth moves/ revolves around the Sun. The Earth's axis is not straight up and down with respect to how it moves around the Sun. Our part of the Earth is titled back, away from the Sun in the wintertime. By the time the Earth has revolved half-way around the Sun, our part of the Earth will be tilted toward the Sun and it will be summertime. In between winter and summer, our part of the Earth will be warming up as the Sun's ray are more and more directly shining on us (springtime). In the fall, as the Earth continues on its journey around the Sun, the Sun's rays will be gradually shining less and less directly on us, our part of the Earth will be cooling off more and more.

"What makes the moon change shape?"
The moon is not really changing its shape. It is just changing the amount sunlight that it is reflecting on to us.
One side of the moon is always facing the Sun. (Just like on Earth, there is always daytime somewhere. Except for, of course, during an eclipse!) If the part of the moon that has full sunlight is also completely facing us, then we will see a full moon. If that part of the moon is not facing us at all, then we will not have any sunlight reflected to us from the moon. The moon will appear "black". We call that a new moon, even though we see nothing at all!
How much of the sun lit part of the moon is facing us depends on where the moon is in its orbit about us. If the moon is between the Sun and the Earth (but not directly, or else there would be a solar eclipse!), then we would have a new moon. During approximately a half month's time, the moon will revolve halfway around the Earth, and the sunlit portion of the moon will "grow" more and more. This is referred to as the "waxing" of the moon. When the moon is on the back side of the Earth (but not directly, or else we would see a lunar eclipse!), we would see the full sunlit side of the moon, a full moon. As the Moon continues on its revolution about the Earth, it slowly, but surely, turns its dark side to us. Exposing less and less of its sunlit side. We call this the "waning of the moon."