Ask-a-Physicist

Negative Mass

In general relativity, gravity is described as a distortion of space time. Most vulgarized books use the simplified image of a 2D plane being bent downwards by a mass, so that any matter traveling in the area would have to follow the bending of the plane, which would then explain why things are attracted to one another.

Keeping the same simplified metaphor, could we imagine something that would bend the plane upwards, thus causing objects to be repelled? Would such a thing be considered to have negative mass? Is the concept theoretically possible?


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Wind Turbine Speed 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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Never-ending light in a room full of mirrors

If you had a light in a room which was entirely sealed with mirrors, then switched the light off, would the room stay lit?

Would the light just keep reflecting off the mirrors?

Would it slow down? Perhaps to the point where it is no longer visible?


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Basketballs, tennis balls, ping-pong balls, and physics

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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Can particles have negative mass?

It looks like they are looking for positive mass particles at the LHC at CERN. Isn't it logical that there are negative-mass "anti-particles"? Does the LHC have the capability of measuring negative mass?


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