If space is a vacuum, then why doesn’t it suck in all the air from Earth’s atmosphere?

Question Answered by Alana Jensen, Environmental Educator, INL ESER Program    www.idahoeser.com

You may say the answer is because gravity is pulling the air to the Earth and that is true.  Gravity is the reason for the existence of an atmosphere on Earth.

Another reason, however, is that the vacuum of space does not exert any force on the atmosphere at all.  It does not “suck” the air.  We associate the word “suck” with “vacuums,” but vacuums actually do not suck air at all.
If we pump all of the air out of a box and create a vacuum inside of it and we poke a hole in the box, what will happen?  Air will rush into the box and fill it.  Why did it do that?  Was it because the vacuum sucked the air into the box?  No.

What actually happened is that the air pressure around the box is forcing air into the space with no pressure.  The air that fills the box is being pushed by air pressure into the empty space.

Vacuums never “suck” air.  What they do is a provide an empty space and then air pressure forces the air into the vacuum.

On Earth, our atmosphere is air pulled to the Earth by gravity.  We call the pressure of the weight of air molecules air pressure.  The pressure of the air molecules changes as you move upward from seal level into the atmosphere.  The higher you go in altitude, the lower the air pressure.  In face, at the upper limits of the atmosphere, the air pressure reduces to basically nil.

And since there’s hardly any air pressure very high in the atmosphere, there is no force pushing the air into the vacuum of space.

If we could turn off gravity, then the atmosphere would be released and spread into space. 

Make a Vacuum
With the straw just sitting in the glass, the pressure on the surface of your drink is the same all over, including on the little bit of surface inside the straw.

When you suck the air out of the straw, you decrease the pressure inside the straw, allowing the higher pressure on the rest of the surface to push the drink up the straw and into your mouth.

Materials:  Screw-top glass jar, hammer, straw, nail, marshmallows, play-dough

  1. Use a hammer and nail to pierce a hole (big enough to fit a straw) into the lid of a screw-top glass jar.
  2. Stick a straw about 1/2 inch deep into the hole and seal the edges with play dough or molding clay so there’s no way for the air to get out other than through that straw.
  3. Place the marshmallow in the jar, screw the top back on.
  4. Take the air out of the jar, gulp by gulp, through the straw.  Be sure to cover the straw hole between breaths so no air makes it back in. As the air is removed, what happens to the marshmallow?
  5. Now blow into the straw to add air back into the jar.  What happens to the marshmallow?</li
Why it works: When you use a straw to remove all the air from the jar, you created a vacuum. Under normal conditions, molecules of air from the atmosphere are pushing on the outside of the marshmallow. When you remove the air that was once pushing on the outside of the marshmallow, the air trapped inside the marshmallow pushes out (expands) causing it to get larger. The marshmallows shrink when the vacuum broken and air rushes back into the container, reapplying the pressure onto the marshmallow.

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