Day 5

Context

With our background of looking at physical phenomena we will now concentrate on a counter-intuitive phenomena, a box sliding on a table.

Explanation

If you construct a situation where a box is sitting on a table with a string attacted to the end of the box and the string hangs over the edge of the table with a weight on the end of it, a strange thing happens. When let go the box stops at the edge! It must be a pretty smart box to not fall off!

After this class you should be able to:

• Describe what a force is.
• Identify the forces on the box in this situation.
• Use the forces on the box to explain why the box stops at the edge.

Model

Modeling

Here is a model of a box on top of a table as described above. The string goes over a red pulley that doesn't interfere with the box.

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Today we will explore this situation. We can start by identifying the variables associated with this set-up. How many can you come up with?

Next lets focus on the box. How many forces are on the box? What is a force? What direction is each of the forces? Does this help you to identify more variables?

Now lets focus on why it stops at the edge (see Popup Video). What happens to the forces at the edge of the table?

Homework

The homework for this class is on Canvas. It will be to write a conditional argument with the conclusion: "The box stops at the edge."

The next class period will be asynchonous. The time is available to do the webpage homework, but it will be due at the normal end of the class at 12:15 on Friday, so you may want to trade some time before that to do this homework. To start the homework go to Day 6.