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Newton's First Law: Extracting a Hoop from under a Pen Cap

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According to Newton's first law an object continues in a state of rest or uniform velocity unless acted on by an external unbalanced force. In this demonstration we are going to look at the first part of that assertion, namely that an object continues in a state of rest unless acted on by an external unbalanced force. For the demonstration we will use this equipment a glass flask, a wooden hoop and I'll begin by balancing the wooden hoop on the flask. The object is that we are going to experiment with will be the top of my ballpoint pen here and I'll begin by balancing that on the hoop. Now because the pen cap is balanced on the hoop, we know it is directly above the mouth of the flask. Now the goal is to get the cap to drop directly down into the flask and we can do this if we use Newton's First Law correctly. So, you watch what I do very carefully.

Now I'm going to do that again and I'm going to do it the wrong way and we are going to compare what's going on. Ok watch again. That time the cap flipped up into the air. Now let's see what was different between those two methods. You may have noticed the first time when I grabbed the hoop I grabbed from the inside, and the second time I grabbed from the outside. When I grabbed from the inside the hoop deformed, and when it deformed it pulled out. You may notice the top of the hoop comes down. Well what this means is that the top of the hoop will retract from the pen and because it retracts from it immediately there's no way the hoop can exert any force on the pen cap. As a result the hoop cap comes out very quickly and the pen cap just falls down. The pen is only acted on by the external force of gravity, so it will fall straight down into the flask. There's no horizontal force that would make it fall one way or the other. Now let's see that one more time.

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