Ask-a-Physicist by Topic
Space & the Universe
Does Einstein's relativity of simultaneity mean that two events cannot be simultaneous or that we cannot prove that two events occurred simultaneously?
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Assume two photons are moving in opposite directions from each other from a common light source. How fast would they be traveling relative to each other? Twice the speed of light? If the speed of light is the ultimate speed limit in the universe, how can something travel twice that speed?
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Prof. Brian Cox recently stated that the universe is 100 billion light years in diameter. Since the universe is no more than 14 billion years old and nothing exceeds the speed of light, shouldn't it be about 28 billion light years in diameter, not 100? Find out the answer »
How was the universe created if physics states matter can neither be created nor destroyed? Find out the answer »
If you shake the sun, how long would it take before it had an effect on the position of the earth?
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Why does a stationary body above the surface of the earth not change its position after some time while the earth is moving? Suppose if we place an object above the surface of the earth, would it be at the same position after some time and why? Find out the answer »
Question: I want to ask why water is shaped like a ball when it is in space without gravity? Find out the answer »
Would a vertical pipe 50 miles long, one end at or near sea level and the other end in space, suck air into space? It seems as though the vacuum of space should create a flow through the pipe since the pressure at each end is different. - P Find out the answer »
On earth, two objects of different masses fall at the same rate. However, in space, larger masses exert greater gravitational attraction than smaller masses. This seems inconsistent. What am I confusing? - DD, Miami, FL Find out the answer »
Why are the earth and other large celestial objects always spherical? – SP, Mumbai, India Find out the answer »
In his book "Understanding Physics," Isaac Asimov writes "As the earth rotates about its axis, the surface of the earth is continually undergoing an acceleration inward toward the center of the earth (just as the moon does in revolving around the earth." Does that mean that the acceleration on the surface (g = 9.8 m/s2) is directly related to the centripetal acceleration of an object traveling in a circle (a = v2/r)? - DW, Raleigh, NC Find out the answer »
How do I explain the difference between the following two situations to my junior high son: (1) The horizontal velocity of a bullet fired horizontally from a gun has no effect on how long the bullet takes to hit the earth, i.e., how long it takes gravity to bring the bullet down to earth. (2) The horizontal velocity of the Space Shuttle orbiting the earth does affect how long it takes for the Space Shuttle to hit the earth. The velocity of the Space Shuttle makes it keep missing the earth in its free fall. – MMH, Ohio Find out the answer »
Why do we see only one side of the moon and the other side is permanently hidden? - KS, Vienna, Austria Find out the answer »
