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Subject: Science , asked on 1/4/13

# With the help of an experiment demonstrate that air exerts pressure.

A very easy experiment to show that air exerts pressure:

Experiment: Take a plastic bottle ( the thinnest plastic that you can find). Suck the air out of the bottle. You can do this by using a vaccum pump.

Observation: The bottle distorts in shape as the air is being sucked out the bottle.

Conclusion: The air outside the bottle exerts pressure on the bottle because of which the shape of the bottle is altered.

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 Materials needed:n                                 Experiment In                                Bionic Fingern              1.  One heavy rubber plunger (to unplug a sink).n              2.  A stool or chair with a smooth seat.nn                                 Experiment IIn                               The Collapsing Cann              1.  One empty gallon (or 4-5 liter) can, or any other tin cann                  that can be closed off air-tight.n              2.  A hot plate or burner and tripod.nn                                 Experiment IIIn                             The Balloon In A Flask                1.  An Erlenmeyer flask (150-200 ml).              2.  A round balloon with a large mouth (uninflated).              3.  A hot plate or burner and stand.  Strategy:n                                 Experiment In                                Bionic Fingern      1.  Make a small hole in the plunger with a scissor's point.n      2.  Show the students the plunger and ask:  "What is under the plungern          when I place it on the table?"  (anticipated answer: 'nothing').n      3.  Ask one of the students to come up and put his/her cheek close to the n          hole in the plunger.n      4.  Push the plunger in: air rushes out and blows against the cheek!n          Air occupies space!n      5.  Show the students the plunger on top of a stool.n      6.  Tell them that you possess a bionic finger and that you can holdn          down the plunger against the stool with one finger.n      7.  Push down on the plunger and hold it down with one finger coveringn          the hole (a wet finger will work better), and ask a student to come n          up and pull the plunger up.n          The whole stool will stick to the plunger and be lifted!nn                                 Experiment IIn                               The Collapsing Can         1.  Put about 20 ml of water in the can (just enough to cover the bottom)          and heat it over the hot plate or burner.      2.  Let the water boil vigorously for about 2 minutes (vapors should          come out of the can).      3.  Take the can with the boiling water off the heat (don't burn your          fingers!) and immediately close off with the cap very tightly.      4.  Let it stand upright on the table and cool off to room temperature,          or, for faster results, cool off with wet towel.                                  Experiment III                             The Balloon In A Flask        1.  Put a little water (about 20 ml) in the flask and heat it to a boil.      2.  Let the water boil vigorously for at least one full minute.      3.  Take the flask off the hot plate and immediately place the balloon           with the mouth over the flask's mouth.      4.  Let cool slowly at room temperature (the balloon will be pushed          inside out into the flask).  Performance Assessment:n                                 Experiment Inn    Have students collect items that operate on this principle:  suction cup ndarts, soap dishes, coat hooks, portable pencil sharpeners, dashboard cups, etc.  nHave students make comments or write poems about how they use "Air pressure in ntheir lives." nn                                 Experiment IInn     Set up four work stations for students to be assigned to for an experiment nusing soda pop cans.  Fill each can with 5 ml of water and heat it over the hot nplate or burner.  Let the water boil vigorously for about 2 minutes.  Using a npair of tongs take the pop can with the boiling water off the heat.  Use the ntongs to grip the bottom of the pop can.  Invert the can in a pan of cold water.  nExplain what happen?  (The can popped, and crushed immediately.)  Why? nn                                 Experiment IIInn     Have students divide a chart into two parts.  Label one side "Air pressure nhelps" and the other "Air pressure hinders."  Brainstorm ways in which air npressure helps people.   Record ideas on the chart.  Have students be on the nlookout for instances of air pressure helping/hindering people.  Add these to nthe chart. nnConclusions:n                               Bionic Fingern                             n     When holding the plunger down with one finger, the hole was covered and nthis prevented the air from coming back in under the plunger, causing a lower npressure under it.  A moist finger works better to plug the hole because the nwater acts as a seal.n    The force holding down the plunger is equal to the surface area of the nplunger multiplied by 1 kg (about 75 kg for a plunger with a 10 cm diameter). nn                              The Collapsing Can             When the water vapor which pushed out the air (which took up the interior space of the can) after heating was allowed to cool, its volume was reduced by approximately 1000.  When the volume decreased inside the can, the outside pressure crushed the can.      The total force working on the outside of the can is the total of the can's surface area in cm2 multiplied by 1 kg.                               The Balloon In A Flask        By boiling the water in the flask, it was changed from the liquid state into the vapor state.  The cooling of the flask will slowly condense the water vapor and thus create a partial vacuum in the flask.  This will cause the balloon to be pushed in and the atmospheric air pressure will further blow up the balloon inside the flask.
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As we know air is everywhere and we can't survive without air. It consists of various gases, dust particles, water vapors, etc. Air exerts a particular pressure on every single thing. Air pressure is calculated with the help of an instrument called barometer and according to it, the Earth's atmospheric pressure is 14.7 psi (pounds per square inch). We can't feel this pressure because it is everywhere. But if we are in a vacuum or in outer space where there is no air we have to use pressurized suits to protect our body. This is the reason why astronauts wear space suits. Here we are going to take a look at some air pressure experiments which will prove the existence of air pressure and will show that it has weight too.

Interesting Experiments to Measure Air Pressure

The experiments given below are easy to perform and need few things which are easily available at home.

Marshmallows Experiment
Take a glass jar and empty it completely. Add small pieces of marshmallows inside the jar and seal it with a wine vacuum cork. Attach a manual pump over the cork and try to pump as much air out of the jar as you can. This will make the marshmallows pieces swell and you will observe them growing. Now break the seal. As soon as the seal breaks and air comes rushing inside the jar, the marshmallows cramp down and return to its old size.

Water Glass Experiment
This is one of the best experiments to measure air pressure. Take a glass and fill one-third of it with water. Place a cardboard over the mouth of the glass. The cardboard should be bit bigger than the glass' mouth. Now apply some pressure on the cardboard from the left hand and invert the glass with the right hand. Slowly remove the hand and see what happens. The water does not fall from the glass, retaining the cardboard and the water in the same place as before. This takes place because the air pressure outside, i.e., 14.7 psi, is heavier than the combined weight of water and air inside the glass.