Water Waves: Surface Disturbances Due to Energy Transfer
Water waves behave in a similar manner to waves moving through a rope. A rope moves up and down as the waves move forward, but the rope does not move forward with the waves. Similarly, waves pass through water but do not carry the water with them. It is the wave energy that moves forward.
In this project, you will learn about water waves and model their structure and movement. You will use models to distinguish between movement of water molecules and wave energy.
Purpose: To model the parts of a wave.
- Two 5 × 8-inch (12.5 × 20-cm) index cards
- Transparent tape
- Sheet of typing paper
- Colored, transparent plastic report folder
- Black marking pen
- Along a long edge of one index card, centered left/right, cut a 3 × 4-inch rectangular U-shaped piece out of the card (discard the piece).
- Place the cut card on top of the second index card with the cutout shape at the top.
- Secure the two cards together with tape only on the long sides (top and bottom). Do not put tape on the cut-out part. These connected cards will serve as the wave viewer.
- Fold the paper in half, long sides together.
- To make a wave for your viewer, unfold the paper and lay it over the diagram of the wave in Figure 21.1A: match the corner of the paper formed by the fold line and the paper's left side with the corner of the diagram where the dashed lines meet.
- Trace the wave diagram, including the letters T and C.
- Move the paper to the left until the right end of your traced wave touches the left end of the wave in the diagram. Make sure the fold line of the paper is lined up with the horizontal dashed line (see Figure 21.1B). Then repeat step 6.
- Repeat step 7.
- Refold the paper so that your traced waves show. Insert the paper into the viewer from the side with the folded edge at the top so that the waves show through the cut-out window of the viewer.
- Move the paper strip sideways so that the letter T of one wave is centered in the cut-out window of the viewer.
- Cut a 4 × 6-inch (10 × 15-cm) piece out of the plastic folder (discard the folder).
- Lay the plastic piece over the window with the long side of the plastic piece along the top edge of the viewer.
- Tape the plastic piece to the top of the viewer so that the plastic can be lifted or lowered over the window.
- On the plastic, with the black marker, label the wave height and wavelength, as shown in Figure 21.2.
- Hold the bottom of the viewer with one hand and pull the paper sideways through the viewer until the letter T of the next wave is centered in the window. Observe the wavelength C to C) and the wave height (T to C) of this wave.
The viewer shows three waves, each with equal wavelengths and wave heights.
A wave is a disturbance in a material, such as the surface of water, that repeats itself. Most waves are caused by the wind blowing across the surface of the water. Waves move across the surface of the water. The water itself does not travel with the waves but moves up and down instead.
The highest part of a wave is called the crest (labeled C in the model) and the lowest part is called the trough (T). The horizontal distance between similar points of two consecutive waves is called the wavelength. The vertical distance between the crest and the trough of a wave is its wave height.