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Centripetal Force - Bungeeman in Circular Motion

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Now we are going to look at Newton's first law in a different way than we've been doing. Up until now, we have been looking at objects moving in a straight line, either speeding up, slowing down, or staying at the same speed. But Newton's law deals in general with objects whose velocity may or may not be changing. We know that velocity is a vector and has both magnitude and direction. And so, in this demonstration, we will be looking at changes in direction. Again, Newton's first law says that an object remains at rest or constant velocity unless acted upon by a net external force. In this particular case, we are going to look at the force causing the object to change its velocity by changing its direction. We do this by swinging an object in a circle. We are going to use bungee man here for the object that we are going to swing in a circle. And as it swings in a circle, as you know its velocity vector is tangent to the path, and that direction is always changing as bungee man swings. So let's take a look at the force that is causing that direction to change. The force must be coming somehow from the elastic here, and the fact you an see how big that force is. So I'm going to start swinging bungee man like this, its not very stretched, but as I swing faster and faster, then the cord stretches more and more. Let's go down here slow to begin with, and then speed it up. And so you can see that more and more force is being applied. That force is being applied first by my hand, to the spring, and then from the spring to bungee man, and that force is a force that is pulling bungee man to the center of the circle.

So in conclusion, of what we have seen, by applying a net external force, in this case a circular inward force, we are able to change a object's velocity vector.


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