In a previous demonstration, we put a boiled egg into a flask with a mouth narrower than the egg. The challenge is now to remove the egg from the flask without breaking it.
Bunsen burner or candle
Pour some water into the conical flask.
Invert the flask quickly over a tray such that the egg seals the mouth of the flask, preventing the water from coming out.
Light a flame and place the part of the flask with water over the flame. This will help prevent the heat from cracking the flask.
Place a tray under the mouth of the flask as the egg slides out to prevent a mess.
The flame heats up the air and the water in the flask. The heated air expands while some of the water vapourizes. With the increase in amount of gas and temperature, the pressure within the flask increases.
This classic physics demonstration is used to show the effects of pressure difference between the atmosphere and a cooling volume of air. With a set of clean apparatus, you can even have the egg for a snack after that.
Flask or glass bottle with mouth smaller than the egg
Paper measuring about 2 cm by 5 cm
Peel the hard-boiled egg.
Light the piece of paper and drop it into the flask.
Place the peeled egg on the mouth of the flask such that the egg seals the flask.
Observe the egg being sucked in while the flame dies.
When the burning paper enters the flask, it causes the air within the flask to heat up and expand, with some escaping from the flask. When the egg seals the flask, the flame dies as the paper is about to be burned up while oxygen is also running out.
The air then cools down and the pressure within the flask drops. The pressure due to the atmosphere acting downward on the egg is then greater than that acting upward due to the pressure of the cooling air. This pushes the egg into the bottle.