# Ask-a-Physicist by Topic

## Material Science

My friend and I are having a debate on wind turbines or anything that travels in a circular motion. One of us says that the very tip of the turbine blade is traveling faster than the inner part that is close to the axis. We both agree that it has the same rpm, but what part travels at a faster mph?
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I understand what happens and why, when I drop a tennis ball that is resting on top of a basketball. What I am trying to figure out is, why do I not get the same results with a ping pong ball on top of a basket ball. Any ideas?

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My 9 year old wants to know if a single atom exists in a certain state of matter — or must it be associated with other atoms in order to define a state?

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My 4 year old would like to know: "If marbles are made of glass then why don't they break when you throw them?
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On Saturday, I accidentally left a full cup of diet soda sitting in my car. It was originally full of ice, which of course melted over the course of a day and a half. When I got into my car on Monday morning, the straw was just over half full of soda, extending about 2" above the full level of soda in the cup. This condition held constant for quite some time, even when the cup was lifted and jiggled/disturbed. Once I had taken a tiny sip, the level of soda in the straw went back down to where I would have expected to find it (at the same level as the soda in the cup). Given that this was a standard lid (with an opening at the top for the straw that is certainly not airtight, nor was the top opening of the straw airtight at all) I could not imagine how the soda in the straw was being pushed or pressured to a higher level than the soda in the cup. The weather over the weekend was cold, but not freezing, averaging in the low 50's. Why did the liquid level in the straw from my soda rise above the liquid in the cup after being left in my car for the weekend?
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Do laws of physics pose limitations to biological evolution?
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Since the earthquake in Japan the country has been having trouble with their nuclear energy plants and possible meltdown. The question is why aren’t they using lead to absorb the radiation?

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How when pressure is decreased, volume increases?

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How do the machines that concentrate oxygen out of the air work? These machines are used by people with breathing problems - DK, New Orleans, LA
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What is mass? I thought mass was the same as weight, but my friend pointed out that in orbit you have no weight but you still have mass. So what actually IS mass? — TP, London, UK
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My brother asked me if there's a difference in weight between an empty and a full hard disk. He was kidding, but it made me wonder if there might be a small difference on the molecular scale. Is there? — RVO, The Hague, The Netherlands
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How does a catalytic converter work? - WK
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Why does a steel ball bounced on a steel surface bounce higher than any other ball on the same surface? - JL, California
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Do bubbles last longer in cold weather or hot weather? Why? — A, Alpharetta, Georgia
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We're confused about the difference between fluorescent and halogen bulbs. Fluorescent bulbs are classified as hazardous waste because they contain mercury. Do halogen bulbs also contain mercury? - LR and APM, Washington, DC
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What causes the smoke produced when you extinguish a candle flame?— SB, Plymouth, England
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If you fell into a swimming pool full of Jello, would you be able to swim to the other side? — LM, Charlottesville, VA
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