3 questions 100927

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course PHY201

9/27 1:25pm

3 questions 100927 *****.

Careful. Don't put your name into the document.

In class the other day, you said that the magnet was a conservative force. What is this and what is its application?

A conservative force conserves energy. The work done to bring the magnets together is recovered (in this case mostly in the form of kinetic energy) when the system is released.

2. In chapter 4, Newton’s 2nd law of motion states that the acceleration of an object is directly proportional to the net force acting on it. Does proportional mean the same thing as being equal and opposite to?

To say that two quantities are 'directly proportional' is to say that the ratio of the quantities is constant. So, for example, if you double one quantity the other doubles as well; if you decrease one quantity to 1/3 of its original value, the other decreases to 1/3 of its original value.

This is equivalent to saying that the graph of one quantity vs. the other is a straight line through the origin.

So the ratio of force to acceleration is constant, and a graph of force vs. acceleration is a straight line through the origin.

In the experiment with the paper clips and toy car, with the clips suspended over the edge of the table, you constructed a graph of acceleration vs. force, where the force was indicated by the equivalent number of small paper clips.

3. I understand that with our magnets on the rotating strap, the magnet at the end has a higher velocity than the magnet toward the middle. However, how do we calculate how fast each magnet was moving?

The most direct way is to find the circumference of its circular path, which corresponds to 360 degrees of rotation.

If you divide the number of degrees per second by 360, you get the fraction of a rotation covered in a second.

If you multiply the fraction of a rotation by the circumference of the path, you find how far the object traveled.

So you can get the distance traveled in a second, which leads directly to its speed.

We will likely talk about these and others, in class tomorrow.

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