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Table of Contents
A Guide to Microgravity for All Ages
Microgravity Desktop Demonstrations
Materials
Container-Milk Jug
Coloured Fluid
Coloured Fluid
Explanation
Under the influence of gravity, everything falls at the same rate. The reason
that objects like a sheet of paper or a feather fall more slowly than a tennis ball is not that they are lighter, but that air
drag affects them much more. When you pour fluid out of a container, it actually falls out of the container. If, however, the
container was falling with the liquid, they would both retain the same relative position.
Demonstration
Put a small hole in the top (to allow air to enter) and a small hole in the
bottom of a large, unbreakable and sealable container like a milk jug, or a 2 litre plastic pop bottle. Make the holes as
small as possible but large enough that the fluid inside can be seen streaming out when you hold the container up. Show that
the fluid actually does stream out when you hold the container up. Then place your hand over the hole to stop the flow of
fluid and drop the container. Point out that while the container is falling, no fluid streams out of the hole in the bottom
because the container is falling with the fluid.
Materials
Small Heavy Object
Chair, Counter or Ladder
Chair, Counter or Ladder
Explanation
The explanation for weightlessness is contained in the background information
on microgravity (see Weightlessness). When you are in free fall things appear to have no weight because they are falling at
the same rate as you. If you were falling with a heavy object it would feel as if it were weightless.
Demonstration
Weightlessness can be easily simulated. Hold a heavy object in your hands
(make sure it is small enough to fit into your hands) and jump off a chair or a counter at a comfortable height. While you are
falling you should feel less weight in your hands than when you are standing on the ground. Also try jogging with the
objects-there will be periods when the object will feel lighter-this is weightlessness. The effect can be accentuated by
making your strides higher rather than longer. You can also try this on a trampoline if you have access to one.
Materials
Clear Plastic Container
Coloured Fluid
Coloured Fluid
Associated Principles
Air Pressure
Hydrostatic Pressure Variation
Projectile Motion
Hydrostatic Pressure Variation
Projectile Motion
Explanation
Due to the force of gravity, as depth in a liquid increases, local pressure
increases. Similarly, in a stack of books, the ones near the top are much easier to pull out than those at the bottom. This is
because the ones near the bottom are being pushed down on by all the ones above them; the force on them is greater.
In a container of fluid, the fluid near the bottom is under a much greater force, and hence greater pressure, than the fluid near the top. This phenomenon is called hydrostatic pressure variation and is a direct result of gravity.
If a tank has holes at different depths, water leaving the holes at the bottom will travel the furthest horizontal distance. In a microgravity environment books do not push down on one another and the fluid at the bottom of a container is not being pushed down on by the water above it, hence there is no change in local pressure with depth. Water will not squirt out of a hole in the side of a container in microgravity at all and if a pressure is exerted, by a plunger for example, the water will travel an equal distance from each hole, regardless of hole depth.
In a container of fluid, the fluid near the bottom is under a much greater force, and hence greater pressure, than the fluid near the top. This phenomenon is called hydrostatic pressure variation and is a direct result of gravity.
If a tank has holes at different depths, water leaving the holes at the bottom will travel the furthest horizontal distance. In a microgravity environment books do not push down on one another and the fluid at the bottom of a container is not being pushed down on by the water above it, hence there is no change in local pressure with depth. Water will not squirt out of a hole in the side of a container in microgravity at all and if a pressure is exerted, by a plunger for example, the water will travel an equal distance from each hole, regardless of hole depth.
Demonstration
Install holes at various depths in the container and plug them; make one
close to the top and on the opposite side to the others to allow air to enter. Fill the container with a fluid to a level below
the topmost hole and then unplug the holes. Point out that the fluid comes out, perhaps ask why, and also that the fluid from
the hole closest to the bottom of the container travels the furthest horizontal distance-you may only be able to show that it
has the most horizontally level arc. Turn the bottle sideways (make sure that the air hole is above water level) and the
streams of fluid from each hole will be identical because all the holes will be at the same depth.
Materials
Small Clear Sealable Container
Transmission or Brake Fluid Water
Transmission or Brake Fluid Water
Associated Principles
Sedimentation
Hydrostatic Pressure Variation
Buoyancy
Hydrostatic Pressure Variation
Buoyancy
Explanation
In a fluid, particles or globules settle out such that the heaviest settle to
the bottom and the lightest rise to the top. This is caused by buoyancy forces, which are created by hydrostatic pressure
variation. Hydrostatic pressure variation simply means that as depth in a fluid increases, local pressure increases. Pressure
increases with depth due to the increasing weight above pushing down. As discussed, objects in free fall experience
weightlessness, and therefore the lower fluid layers do not experience the weight of the fluid above. Hence there is no
hydrostatic pressure variation, no buoyancy effect and no settling or sedimentation.
Demonstration
Fill the container with a mixture of water and brake or transmission fluid.
Shake up the jar and watch what happens. One of the liquids will settle to the bottom and the other will rise to the top. This
is called sedimentation. If you add a third immiscible fluid and mix them up, you will observe three separate layers.
Materials
Candle Non-flammable Cup, Mug or Bowl
Associated Principles
Convection Buoyancy
Hydrostatic Pressure Variation
Hydrostatic Pressure Variation
Explanation
Candles burn on earth because as the air near the wick heats up, its density
changes and it rises. Fresh air is drawn into the wick, replenishing the needed oxygen for combustion. These are convection
currents. In microgravity there is no convection. As the wick burns, there are no air currents to bring in oxygen, and the
gases around the wick simply collect. As the local oxygen is depleted, combustion ceases and the candle burns out.
Demonstration
Place a burning candle in full view. As it burns, explain convection,
buoyancy and hydrostatic pressure variation. Interrupt convection by placing a cup over the candle, just above the flame.
Carbon dioxide will collect near the wick and as oxygen is depleted, combustion will stop.
Materials
Ten Magnetic Marbles
Tiltable Surface
Tiltable Surface
Explanation
Magnets exert a fixed force on each other. Depending on what other forces
are exerted in a situation, structures and shapes are affected. A group of magnets, such as magnetic marbles, form a ring on a
flat surface. If the ring is placed on a tiltable surface, when the surface begins to tilt, the shape will change from
circular to elliptic. Where before the only force acting was the magnetic force, causing a circular shape, now gravity also
acts causing the ring to deform. As the angle of tilt increases, the ring collapses more and more. In a microgravity
environment these gravity effects are not seen. The ring remains circular in any orientation and does not collapse.
Demonstration
Find a tiltable surface with a lip at the edge so that the marbles cannot
slide off. Start with it in a horizontal position. Put the marbles on the surface and observe that the magnetic attraction
causes them to form a circular ring. Slowly tilt the surface until one side of the ring comes into contact with the lip. As
you continue to tilt the surface, observe that the shape of the ring becomes deformed due to the force of gravity. Return the
surface to a horizontal position and observe that when the effects of gravity are eliminated, the ring returns to a circular shape.
Materials
Bubble Blowing Kit
Associated Principles
Surface Tension
Explanation
Structures on earth deform as gravity and resistive forces balance each other
out. Fluid droplets placed on a surface flatten out instead of remaining spherical as they would if they were in free fall.
Droplets retain some surface curvature because surface tension combats the flattening influence of gravity. In microgravity
fluids retain a spherical shape.
Soap bubbles can be used to simulate the effects of microgravity. The forces of surface tension on a soap bubble are large compared to the weight of the bubble so it retains a circular shape. Fluids have a much greater weight than surface tension, so they change shape. In microgravity, surface tension is the dominant force in dictating droplet shape. Fluid droplets in microgravity retain a spherical shape.
Soap bubbles can be used to simulate the effects of microgravity. The forces of surface tension on a soap bubble are large compared to the weight of the bubble so it retains a circular shape. Fluids have a much greater weight than surface tension, so they change shape. In microgravity, surface tension is the dominant force in dictating droplet shape. Fluid droplets in microgravity retain a spherical shape.
Demonstration
Use a fluid to display a suspended droplet, for example, a drop at the end
of tap or a medicine dropper. Point out the shape of the droplet. The smaller the droplet the more circular it will be. Slowly
add fluid to it. It will assume a parabolic shape. Blow a soap bubble and point out its circular shape. As the weight of a
droplet increases, the deformational effects of gravity alter its shape. Soap bubbles have a very small weight, so even in
gravity, deformation is small and a spherical shape is retained.
Materials
Rectangular Clear Container
Coloured Fluid
Rotating Platform
Coloured Fluid
Rotating Platform
Associated Principles
Centrifugal Acceleration
Resolution of Forces
Resolution of Forces
Explanation
As fluid is spun in a centrifuge, two forces (centrifugal force and gravity)
dominate over surface tension and act on the fluid. As material is pushed to the sides by the centrifugal force, it is also
pulled down by gravity, creating a parabolic shaped surface. In a microgravity environment, since the only force in effect is
centrifugal, instead of the parabolic shape, we will simply see a larger and larger hole develop at the centre of the
centrifuge. A certain rotational speed is required to overcome surface tension, before separation occurs.
Demonstration
Fill a clear rectangular container with a coloured fluid. Set it turning on
a rotating platform. As the container rotates, the surface of the fluid will change from flat to parabolic, and as the speed
of rotation increases, the parabola will deepen.
