MadSci Network: Physics

Re: Will Artificial Gravity increase with an increasing rate of acceleration

Date: Tue Dec 21 04:23:07 2004
Posted By: Andy Goddard, Staff, Teaching and Learning Resources, Strathclyde University
Area of science: Physics
ID: 1103520709.Ph

Hi there!

The short answer is that the acceleration felt onboard the spaceship (your
artificial gravity) will always equal the acceleration of the spaceship.
This is independent of the velocity of the ship. (Velocity and acceleration
are different things). For example, there's only a microgravity environment
- sometimes called wieghtlessness - in the space shuttle once it's safely
in orbit, even though it's travelling at nearly 8 kilometres a second -
here, no rocket acceleration means no "artificial gravity".

The slightly longer answer: Isaac Newton realised that force is
proportional to the rate of change of momentum. In simple terms,

F = m * a

Where "F" is the force, "m" the mass and "a" the acceleration. You can see
from this equation that the acceleration will rise if the mass falls and/or
the force rises. For chemical rockets, where the mass of the spaceship is
mostly fuel and oxidiser, the fall in the mass is quite dramatic, and the
rise in the acceleration is high.

In the shuttle's case, just before it enters orbit, given that the three
main engines can produce about 2278000 newtons in a vaccuum, and the mass
of the shuttle is around 105000kg, coupled to an empty external tank mass
of 26600kg (NASA figures), the equation is:

F = m * a
3*2278000 = (105000+26600) * a

a = 51.9 metres per second squared

Since 1 Earth gravity is 9.8 metres per second squared, the shuttle
astronauts would be subjected to over 5g of acceleration. This is deemed
too much the crew, so in reality the shuttle enters orbit with some
residual fuel left in the tank (thereby increasing its mass) and with the
engines throttled back to maintain around 3 gravities.

I hope this helps answer your question!

Andy Goddard

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