[Lex Computer & Tech Group/LCTG] Here is something I never knew. From an email I get

[john rudy]

If I have a solid object which is 1 light year long and I push it and there
is somebody else on the other end, how long would it take for them to notice
that I pushed it?

When you push on an object - even one that appears completely solid - the
movement takes time to move through the object. In pushing on the object,
you're actually generating a wave that propagates through the object, as
atoms push on adjacent atoms. When a baseball player begins to swing a bat,
the far end of the bat actually lags behind the near end of the bat. The
length of the bat is short compared to the speed at which the effect
propagates through the bat, so it appears to be completely rigid. But the
longer the object, the more noticeable it will be that the force takes time
to move through the object.

And how fast does the force move through the object? At the speed of sound.

And how fast is that? Depends on the substance. Suppose the solid object is
made of steel. Movement would propagate through the object at 5.960
km/second. So if you had a steel object that was a bit less than 6 km long
and you push on one end, someone on the other end would feel the effect 1
second later.

If you had steel rod that was one light-year in length, a force would take a
little over 50,000 years to propagate to the other end.

 

 

John Rudy

781-861-0402

781-718-8334 (cell)

John.rudy at alum.mit.edu <mailto:John.rudy at alum.mit.edu>  

 

13 Hawthorne Lane

Bedford, MA  01730-1047



 

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