A couple of posers...

[Phantom1983]

I was asked these by a venerable old secondary school teacher of mine. They sound like modern day Zen "empty your mind" problems to me...

1. Why are things not upside down when seen in a mirror? What is so special about the up-down direction?

2. Why do microwaves carry the warning "do not use empty"? What will happen if I do use one empty?

An answer to either or both of these would be fantastic (I've been pondering them for the better part of 11 years...)

 

[DrPizza]

1. Should be covered in most high school physics classes... diagram helps the explanation. And, for #1, I assume that you mean a plane mirror (flat) rather than a curved mirror (concave or convex).

2. Go buy a microwave oven at a garage sale... should be able to pick one up for cheap. Plug it in outside (use an extension cord), "just in case." Set the timer to 2 hours. Start. When finished, disassemble.
Sometimes, science is more satisfying when you figure things out through experimentation.
However, before you conduct this experiment with the microwave oven, check for other fun microwave experiments (lightbulb, aluminum foil, LED's, flourescent lights, lit candles, and, of course, the split grape bipole antenna!

 

[Phantom1983]

By far the funniest "microwave curiosity" is a bar of soap. Just put it in, nothing else needed. I first saw this on TV and could not believe it. I won't spoil it but it isn't very dangerous at all.

 

[Corporate Thug]

Originally posted by: Phantom1983
By far the funniest "microwave curiosity" is a bar of soap. Just put it in, nothing else needed. I first saw this on TV and could not believe it. I won't spoil it but it isn't very dangerous at all.

ok, i'll do it

Ivory soap is one of the few brands of bar soap that floats in water. If it floats in water, it must mean that it?s less dense than water. When you broke the bar of soap into several pieces, no large pockets of air were discovered. Ivory soap floats because it has air pumped into it during the manufacturing process.

The air-filled soap was actually discovered by accident in 1890 by an employee at Proctor and Gamble. While mixing up a batch of soap, the employee forgot to turn off his mixing machine before taking his lunch break. This caused so much air to be whipped into the soap that the bars floated in water. The response by the public was so favorable that Proctor and Gamble continued to whip air into the soap and capitalized on the mistake by marketing their new creation as ?The Soap that Floats!?

Why does the soap expand in the microwave? This is actually very similar to what happens when popcorn pops. Here's the secret: All soap contains water, both in the form of water vapor inside trapped air bubbles (particularly important in the case of Ivory) and water that is caught up in the matrix of the soap itself. The expanding effect is caused by the heating of the water that is inside the soap. The water vaporizes, forming bubbles; the heat also causes trapped air to expand. Likewise, the heat causes the soap itself to soften and become pliable.

This effect is actually a demonstration of Charles? Law. When the soap is heated, the molecules of air in the soap move faster causing them to move far away from each other. This causes the soap to puff up and expand to an enormous size. Charles? Law states that as the temperature of a gas increases so does its volume. Other brands of soap without whipped air tend to heat up and melt in the microwave.

 

[jagec]

Originally posted by: DrPizza
1. Should be covered in most high school physics classes... diagram helps the explanation. And, for #1, I assume that you mean a plane mirror (flat) rather than a curved mirror (concave or convex).

2. Go buy a microwave oven at a garage sale... should be able to pick one up for cheap. Plug it in outside (use an extension cord), "just in case." Set the timer to 2 hours. Start. When finished, disassemble.
Sometimes, science is more satisfying when you figure things out through experimentation.
However, before you conduct this experiment with the microwave oven, check for other fun microwave experiments (lightbulb, aluminum foil, LED's, flourescent lights, lit candles, and, of course, the split grape bipole antenna!

don't forget CDs...

I haven't tried this one, but I HEAR it's really cool:
get a glass bowl. Light a match, let it burn down to the wood, blow it out. Put it under the inverted bowl, with a stream of smoke rising up. Turn the microwave on with the whole assembly inside.
Apparently it's pretty neat...

 

[Born2bwire]

Marshmallows, especially Peeps!

 

[Smilin]

Try that shiney plastic that pop tarts come in.

for the record it really does count as metal. burns in a really cool "parched earth" kind of pattern too.

Marshmallows are fun.



This soap thing... is it messy? I haven't tried it.

 

[Smilin]

Originally posted by: Phantom1983

1. Why are things not upside down when seen in a mirror? What is so special about the up-down direction?

It would be hard to put yourself in front of a mirror to test this if you were symmetrical in an up down direction instead of left-right.

You would either have to walk with your lips or see with your toes.

 

[Peter]

Mirror: The point is that the left-right direction isn't flipped over either.

 

[Vee]

Originally posted by: Phantom1983
1. Why are things not upside down when seen in a mirror?

Well mirrors do "turn things upside down". ...In the sense that anything "turns" at all. It's your choice how you turn anything around so that it faces the mirror. Normally people tend to turn things - including themselves - towards the mirror by rotating the vertical axis.

Consider for instance some mirrored writing. It's readable by turning it away from you towards a mirror. When you turn it, you typically exchange the right and left sides. If you don't and flip it instead, exchanging up and down when turning it towards the mirror, you would typically go "oops, upside down" and correct it. But you don't have to. What if the mirrored text is written from the left towards the right as usual, but the letters are mirrored upside down instead? Just flip it towards the mirror, and voila, the text is readable again, with the correct side up.

Look at this pattern:

++++------+
+++------++

One mirror image of that would be:

+------++++
++------+++

If you turn that around facing the mirror, you will get the right side to the left and you will again see the original pattern in the mirror:

If you flipped it to face the mirror around the horizontal axis however, you would see:

++------+++
+------++++

Which proves that mirrors indeed "turn things upside down" as well!

 

[Vee]

Originally posted by: Phantom1983
2. Why do microwaves carry the warning "do not use empty"? What will happen if I do use one empty?

I don't know this. I know very little about microwaves. But, I could make a wild guess that an empty microwave maybe presents some radiation hazard. My speculation is that all those microwaves are reflected around inside by shields. That's fine as long as there is something sucking up the waves. Something has to absorb the energy. If there isn't anything, the energy still has to be absorbed by something in the end anyway. Some of it will probably destroy the oven, but maybe a good deal of the energy will also leak out and be absorbed by the environment? Kinda like a laser.

 

[Markbnj]

Mirror: The point is that the left-right direction isn't flipped over either.

This is correct; it's all perception. The best way to check this is to face the mirror wearing a tshirt with writing on it. The first letter of the sentence is on your right when wearing the shirt, and when you look at the mirror it is still on the right. You're seeing exactly what you would see if you were looking "through yourself" from the back.

 

[Phantom1983]

Originally posted by: Vee

Originally posted by: Phantom1983
2. Why do microwaves carry the warning "do not use empty"? What will happen if I do use one empty?

I don't know this. I know very little about microwaves. But, I could make a wild guess that an empty microwave maybe presents some radiation hazard. My speculation is that all those microwaves are reflected around inside by shields. That's fine as long as there is something sucking up the waves. Something has to absorb the energy. If there isn't anything, the energy still has to be absorbed by something in the end anyway. Some of it will probably destroy the oven, but maybe a good deal of the energy will also leak out and be absorbed by the environment? Kinda like a laser.

The answer I most frequently received is that the microwaves eventually migrate back to the magnetron when no water is present to absorb their energy. The opening for the magnetron is the only real gap in the microwave's interior (microwaves will bounce off the walls, floor and door) so the waves could accumulate in the magnetron and not be reflected back out.

 

[Wreckage]

Originally posted by: Phantom1983
What is so special about the up-down direction?

Gravity.

2. Why do microwaves carry the warning "do not use empty"? What will happen if I do use one empty?

With nothing to absorb the microwaves and turn them into heat, it can cause an adverse effect on the equipment.

Short answer.

 

[Sunner]

Ok, for DrPizza's post, I've heard about all those microwave "experiments", except for the burning candle.
I don't keep any burning candles around at home(and definitely no disposable microwave ovens ), so, what's supposed to happen?