Air Pressure - Egg in a Bottle (Rana Khan)
Rana Khan
version 1
This is a an investigation into “forces” discrepant event in which students make observations of an event and then explain the science that caused the event.
This simple; however complex, investigation is a great attention getter for learning about forces and atmospheric forces.
May the Force be with You
Materials: (per group)
One hard boiled egg with shell removed
One clear plastic or glass bottle that has an opening narrow enough that the egg will not fit through
One strip of paper about one inch by six inches
One box of matches
Procedures:
Light the piece of paper with a match and place the paper inside the bottle
Place the egg in the opening on top of the bottle
Observe what happens
Expected Observations:
As the paper burns inside the bottle, the bottle will fill with smoke. Shortly thereafter, the students will observe the egg begin to slowly change its shape to fit through the bottle opening as it slides through the opening. Suddenly the egg will fall through the opening and land at the bottom of the bottle.
Questions to Ask Students:
What did you observe about the egg? (Common answer is that the egg was sucked into the bottle.)
What force or forces caused the egg to enter the bottle? (Common answers include air in the bottle forced the egg inside or gravity pulled the egg inside.)
Science Behind the Discrepant Event
The burning piece of paper heats the molecules of air in the bottle. This causes the molecules of air to move further away from each other. When the flame goes out, the molecules of air in the bottle cool down and move closer together. This is what scientists refer to as a “partial vacuum “. Normally the air outside the bottle would come rushing in to fill the partial vacuum created inside the bottle. However, the egg is in the way! The “push” or pressure of the air molecules outside the bottle is so great that it literally pushes the egg into the bottle. Gravity causes the egg to fall to the bottom of the bottle.
version 2
Brief Description:
Demonstrate the relationship between temperature and pressure by trying to fit a hardboiled egg into a flask, and then trying to get the egg out of the flask.
Difficulty / Time Commitment:
6 out of 10
Coolness Factor:
10 out of 10
Materials:
· 1000mL Erlenmeyer flask with a mouth of 1.5” diameter (or anything with an opening barely
too small for the egg to fit through)
· matches or lighter
· paper that burns easily
· hard-boiled egg (large or jumbo)
· glass of water
Instructions:
1. Hard-boil a large or jumbo egg.
2. Peel the shell off the hard-boiled egg.
3. Place the egg on the mouth of the flask and observe that it won’t slide into the flask. Then
take the egg off of the beaker.
4. Curl up a piece of paper into a narrow spiral that will fit into the flask.
5. Light the paper on fire and drop into the flask, taking care that the fire keeps burning after it
is dropped into the flask.
6. Quickly place the egg back onto the flask mouth, and watch it slide in.
7. Pour water into the flask to wash out the ashes.
8. Turn the flask upside-down, and make the egg plug up the narrow part of the flask, making a
valve.
9. Blow hard into the flask, holding the flask nearly vertical, and the egg will slide out.
What Happened?
Putting the burning paper into the flask increased the pressure because of the temperature
increase. When the egg was placed onto the flask mouth, the fire suddenly went out inside the
flask and thus the temperature suddenly dropped, thereby creating lower pressure inside the
flask compared to the pressure outside the flask. The higher pressure outside the flask then
pushed the egg into the flask. Blowing into the flask got the egg out of the flask because we
forced more air molecules inside, which increased the pressure inside the flask relative to the
pressure outside the flask.
Basic Concepts Learned:
The egg always goes from high pressure to low pressure, just like the wind blows from high pressure to _ low pressure.
The ideal gas law states that pV=nRT. Pressure (p) can be changed by either changing the
temperature (T) or by changing the number of air molecules (n). (R is a constant.) More air molecules and higher temperatures lead to higher pressure.”