Zero Gravity
No matter if you're in elementary
school, high school, or a triple doctorate astrophysicist, we
all have something in common. We're stuck on Earth. Why? Well,
if we remember Sir Isaac Newton and his apple, the Earth has gravity.
To go into exactly what it is would mean ugly equations and derivations.
Instead, just accept the fact that without a rocket ship, you're
stuck on Earth.
But there are ways to make it seem like you're not on Earth. For
example, when you're on a roller coaster and you're going really
fast over a hill, you feel you're stomach move up into your throat,
right? Well, in a sense, your stomach has escaped gravity for
a second or two. Now imagine an airplane going really fast over
a hill. Well an airplane goes much faster, and the "hill"
is much bigger, so the time in zero gravity is much longer. Even
better, if you're inside the belly of the airplane, YOU are in
zero gravity. Basically, you float.
So why does our experiment need to be in zero gravity? Would you
like the technical explanation or the non-technical explanation
(scroll down for non-technical)?
TECHNICAL
Rayleigh-Taylor flow is a body force driven flow triggered by
the acceleration induced upon it. On Earth, we are in a constant
1g environment. To vary the acceleration, we would initially have
to start at 1g = 9.8m/sec2 = 32.2 ft/sec2. If we wanted a final
to initial acceleration ratio of about 10, this means we'd finish
at 10g = 98 m/sec2 = 322 ft/sec2. By reducing the magnitudes of
acceleration by a factor of 10, we also reduce the final velocity,
track length, and final momentum by a factor of 10 as well. The
following table shows an example:
Table 1: Theoretical Test Parameters
| m (lbs) |
t (sec) |
ai (g) |
af (g) |
Vf(mph) |
d (mi) |
Pf (lb*ft/sec) |
| 12 |
20 |
1.0 |
10 |
>2400 |
8.5 |
>42000 |
| 12 |
20 |
.1 |
1.0 |
240 |
.85 |
4200 |
Keep in mind that because of the direction of acceleration,
the track length needs to be completely vertical. To comply with
our volumetric constraints, the time of testing is reduced and
our parameters are then as such:
Table 2: Actual Test Parameters
| m (lbs) |
t (sec) |
ai (g) |
af (g) |
Vf(mph) |
d (m) |
Pf (lb*ft/sec) |
| 12 |
1 |
0.1 |
1 |
13.5 |
4 |
240 |
Note that the final to initial acceleration ratio is still 10:1,
meaning we get the same data for what would be millions of dollars
less.
NON-TECHNICAL
For our experiment, we want to see how gravity affects fluids.
Unfortunately, because the Earth has so much gravity, the fluids
fall too fast and it’s hard to test it without a building
that goes 20 miles into the sky! Instead, if we test in zero gravity
and connect a motor, we can control how fast the fluids fall.
This way we don't need that huge building.
