Being "Pushed" Around
Non-Compressibility of Water
Levels 1&2

Connection with the Curriculum:

Sometimes a vessel will experience a "push" from the side of a channel that requires an adjustment to steering to stay on course. Water, trapped between the vessel and the channel side, is not compressible. A force proportional to the momentum of the passing vessel is generated by the interaction between the water, the ship, and the channel side. This can be a very dangerous situation.

Objective:

The students will understand that water cannot be compressed and be able to explain the importance of this fact in their daily lives.

Materials:

1. One 2-liter plastic soda bottle
2. One glass eyedropper (can be obtained from most drug stores)

Procedure:

1. Bring an empty 2-liter pop bottle and wash and remove labels.

2. Fill the pop bottle with water.

3. Partially fill the eyedropper so that in a cup of water, the eyedropper just barely floats below the surface.

4. Place the eyedropper in the 2-liter bottle and screw on the lid.

5. Squeeze the bottle(when they do this, the eyedropper will go down). Ask students to try and explain what happened. After the students have formulated some responses, question them as to why they thought that.

6. Squeeze the bottle again slowly and observe the water level in the eyedropper.

Tying it together:

As pressure is applied, the water level in the eyedropper goes up. The air is compressed and more water is forced into the eyedropper making it heavier and causing it to sink.

In designing navigation channels, the likely forces affecting ships are taken into consideration. If the maintenance of channels is not sufficient to maintain design parameters or the size of vessels using the channels exceeds the design vessel size, maneuverability in the channel is made more difficult.