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This page last updated:
25 January, 2007

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eeps media

Hanging Impulse

Check out this graph:

This is a Force-Time graph for the tension in a string when you drop an object (a hexnut in this case) attached to the string, and the object "bounces" when it reaches full length.

You can see that the blips are the bounces; this is just like the Impulse lab in the book except the force probe is above the object and you (therefore) don't need platforms.

How do you suppose the graph would be different if...

  • You dropped the nut from a different height?
  • You dropped something heavier or lighter?

To study these questions, it will be useful to quantify some characteristics of the graph. For example, for each run you might want to record the maximum force in the first impulse, or the time between the first two bounces.

Ultimately, you'll want to figure out how these quantities depend on the height (and on anything else). You can do that through the data, or through your understanding of physics—or through a combination of the two.

A practical application might involve the breaking strength of the string. Suppose it's 200 N. Your force sensor goes up only to 50 N. Can you make a mathematical model that will tell you, for a 500-gram weight, how far it can fall and still not break the string?

We hung a Vernier dual-range force sensor off a stand, and off the edge of a table so that there was a clear drop from the hook to the floor. We attached a regular old string about 70 cm long to the hook, and at the other end tied on a hexnut (weight 0.156 N).

This particular drop was from a (net) height of about 40 cm.

Data aquisition and analysis is using Fathom.