WAVES

Students:

3rd grade and up, max of ~20 students, min of 6

Note:

Participants will be very likely to get WET! A good summer project for scence camps.

Objective:

To use the amplitude and frequency of waves in water to judge the size of objects tossed into the water, and the distance and angle to the source (when one cannot "see" the source). Distance and angle will be hard to do, and will lead most groups to realize that without more information, distance and size are hard to deconvolve. Teams taking on the more sophisticated approach described below should come away with an appreciation of the process of developing, building, testing, and calibrating an instrument. A wading pool is a lot less tricky than space!

Minimum Facilities Required:

• A sheet of still water - preferably quite large
  • Could be a wading pool
  • Could be a pond
• A collection of objects of graduated sizes and weights; small s tones, etc.
• A device that will bob up and down while tethered in place, for example, brightly colored fishing float attached to a stick
• Stopwatches
• For advanced groups or groups that have access to equipment, a strip-chart recorder that transforms the action of the float into a time-stepped trace on paper. An ingenious group could 'invent' this with an electric motor or clockwork motor from an erector set and a felt-tip pen attached to the float. Do NOT use anything but small batteries because of the risk of electric shock. Writing implements and surfaces should work in the wet or be protected - a challenge for the engineering team.

Organization:

Depending on the level of sophistication, the group can be split up into only two groups, tossers and measurers, or into several groups each in charge of a portion of the process. In the two-group mode, the students take turns tossing rocks into the water, while the other group splits up into pairs or trios and records the how many times the float bobs up and down in a short period - e.g. 30 seconds. The toss zone needs to be at least 20 feet from the float or the ripples will be too close together to measure. It also needs to be some distance away from the measurers for safety. The tosser group should be positioned to toss away from the measurers.

In a more sophisticated situation, one group is charged with the responsibility of trying to develop the measuring device (engineering team). They can investigate a 'systems' approach, developing a requirements document, a design, and specifications. Another group (the theorists) is charged with figuring out what 'ought' to happen. Another group (the technicians) is employed rigging up equipment and finding rocks. When the experiment is set up, all groups cooperate to improve the measurement technique and interpret the results.

Procedure:

The float measuring device is placed in the water and calibration runs are attempted in which a series of 'known' rocks are tossed into known zones. The zone can be varied so that a matrix can be constructed and graphed of zone/stone-size. The stones should be dropped or lobbed in

a consistent way rather than hurled. Then the measurement team is shielded from the rock-tossing team who are free to drop any rock in any zone (which they record). Using its calibration data, the measurement team tries to figure out the sequence.

If the team has a high level of function and appropriate equipment, they may realize that they can use the shape of the waves as a clue to the arrival direction.

The calibration/test sequence can be iterated a number of times to allow the group to improve its equipment.

Enhancements:

Use two synchronized wave-sensing stations a nd see if there is information in the comparison of their results. If you can see the angle of approach of the waves on both, the normal to their direction of arrival should intersect at the location of the rock splash.

Reflections of the waves against the side of the pool and back to the sensors will set up interference patterns. Is there any way of figuring

Tie-in to Ulysses URAP experiment:

Ulysses measures the amplitude and frequency of waves impinging on the spacecraft antennas to identify a variety of oscillations known to occur

Tie-in to Earth:

Wave obervations are used in detection of submarines and surface vessels as well as in radar sensing of planes.