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Egg-zactly the Point

This experiment is the result of breakfast. I needed to have a quick bite and then get to work, packing for a trip. Instead, I wanted ham, eggs and hash brown potatoes, so I compromised and decided to work on an experiment that I could research while cooking the breakfast I wanted. This is an experiment that has been used in physics classes for quite a while, but I am hoping that most of you have not seen it. We will be using an egg shell to show some interesting things about the scientific laws of motion. You will need:

- several egg shells
- a ball point pen

First, crack some eggs. Crack the shell carefully, to get them basically into two halves. Use the egg itself for something yummy. Wash the shells and set them aside. Take a ball point pen and hold it in your fist, with the point sticking upwards. Balance one of the egg shells on the point of the pen. Now, the idea is to bang the pen against the table top so that the point of the pen punches a hole through the egg shell. Try this and watch carefully to see what happens.

Did it make a hole in the shell? Probably not. Instead, the shell probably either rattled around on the point or fell off. Ready to try something different? Put the egg shell back on top of the pen. This time, instead of holding the pen in your fist, hold it about a foot above the table top and drop it so that it lands on its end. What happened this time?

When you drop the pen, it easily makes a hole in the egg shell every time. Why is this? Why would dropping it work when banging it with your fist would not? We need to think carefully through what is happening each time.

Think about it, and when you think you know the answer, then continue.

First, when you held the pen in your hand and banged it on the table, your hand was moving the pen downwards faster than the egg shell was falling. When the pen hit the table, it bounced back and most of the energy was absorbed by your hand. Then the egg shell caught up and landed on the pen. Since the egg shell is very light, it did not have enough energy of motion to force the point of the pen through the shell.

When you dropped the pen, both the pen and egg shell fell at about the same speed. The shape of the egg shell caused enough air resistance to slow the egg shell a tiny bit, but not much in the short distance it had to fall. The pen hit the table and bounced back. Just as it started to bounce upwards, the egg shell hit it. The pen was moving upwards, and the egg shell was moving downwards. The combination was enough to force the pen point through the shell.

This is the kind of science experiment that was very popular in the days before TV and radio. During Victorian times, science challenges such as this were common as after dinner entertainment. They usually involved giving the group a challenge, such as using the pen to pierce the egg shell. After everyone tried and failed, then the challenger would show them the trick and explain the science behind it. Sounds like a fun idea for a party to me.