Pressure Bottle Barometer
(Teacher or Parent Instructions)
This project teaches students the fundamental concepts of pressure and how they relate to the temperature of a liquid. Upon the completion of this project, students should understand enough about pressure so that they are able to predict the weather through the use of a barometer.
Basic
Principles of a Barometer
Atmospheric pressure, the air pressure in the surrounding area, can be determined through the use of a barometer in which the height of a column of mercury or water is measured. The measured height can be converted into pressure using the following equation:
where:
PO = The pressure at the reference point (This is the point on the bottle where the
tape is applied)
P = The pressure that you are trying to determine
= The density of the fluid
(mercury = 13550 kg/m3, water = 999 kg/m3)
g = The force due to gravity (9.8 m/s2 or 32.2 ft/s2)
h = The change in height of the liquid inside the barometer
** It is not necessary for the students to understand this equation.
Results
of Homemade Barometers
At higher temperatures, there is a higher pressure within the bottle and therefore when the water in the bottle cools or if the bottle is submerged in cold water, the pressure inside the bottle will decrease and the water level in the straw will go down.
The students will notice that over time, the water level rises and falls. Tell the children to make sure to pay attention to the change in weather and its relation to how the water level inside the straw changes.
The water in the tube rises and falls because of air pressure exerted on the water in the glass. As the air presses down (increased atmospheric pressure) on the water in the glass, more water is pushed up into the tube, causing the water in the tube to rise. Similarly, when the air pressure decreases on the water in the glass, some of the water will move down out of the tube, causing the water level in the tube to fall. The change of barometric pressure will help students to forecast the weather. Decreasing air pressure often indicates the approach of a low pressure area, which often brings clouds and precipitation. Increasing air pressure often means a high pressure area is approaching, bringing with it clearing or fair weather.
Children's
Instructions are Attached
Paper Plunge
(Teacher or Parent Instructions)
This
project teaches students the princples behind air pressure. Upon completion
of this experiment, students will learn more about the principles behind air
pressure and mass.
Basic
Principles of the Paper Plunge
In order for this experiment to work properly, the glass must be plunged
straight down into the water. This will prevent any air from escaping. The
air is what prevents the water from entering the cup and coming in contact with
the paper. In order for the water to enter the cup, the air must first be displaced.
Air tends to rise, so it moves to the top of the cup to try and escape, only
to find a solid cup. With the air trapped, the water tries to push into the
cup, but will merely compress the air molecules more. This will increase the
air pressure, which will in turn push against the water and prevent it from
entering the cup. The deeper the cup is placed in the water, the harder the
water will push against the air to try and get into the cup. However, no matter
what the water tries, it will not be able to enter the cup and touch the paper.
If the cup is not plunged perfectly straight down, air will be able to
escape from the cup, which will allow the water to flow up into the cup. This
will possibly cause the water to touch the paper if the student is not careful.
Crushing with Air
(Teacher or Parent Instructions)
This
project will teach students the princples behind air pressure and its curshing
abilitiy.
Basic
Principles of a Barometer
Once
hot water is poured into the soda bottle, this increases the air pressure and
energy of the air inside the bottle. This causes the air to flow out of the
bottle, into the atmosphere. Once the student seals the bottle however, this
will cause the bottle to have a lower air pressure than the atmosphere. However,
the air molecules inside the bottle are full of energy from the heat, and therefore
will push against the bottle walls, keeping the bottle in its proper shape.
When
the bottle is placed is cold water, the temperature of the air will drop rapidly.
This causes the air molecules to lose their energy and begin to slow down.
This causes the air pressure inside the bottle to drop. Since the bottle is
sealed, there will be no more air to try and equalize the air pressure in the
bottle. Thus, the air pressure outside the bottle will be sufficient to overcome
the pressure inside the bottle and crush it.
Seal with Air
(Teacher or Parent Instructions)
This
experiment will teach students about the power of suction and air pressure.
Basic
Principles of a Barometer
When
the water is poured into the cup, air is displaced from the cup. When the plate
is placed on top of the cup, a seal of sorts is formed. Once the cup is flipped,
the water willhelp complete this seal and prevent any air from entering the
cup. This causes a suction effect. If there is any hole in the cup or if the
plate doesn’t fit relatively tightly onto the cup, this will fail and the water
will spill all over the place.
For
the suction effect to be created, the water cannot exit the cup. The plate
and to a degree the water itself forms a seal and prevents air from entering
the cup. The air in the cup will rise to the top, and try to push out without
success. Since no new air can enter the cup, only gravity will be acting on
the water to try and pull it out of the cup. However, for the water to exit,
something must take its place in the cup. If the water was somehow able to
exit the cup, a vacuum would be formed. Nature typically dosen’t like vacuums,
so the water is held in, thus holding the plate as well.