A duck floats on a pond while ripples from a splash spread past it. The ripples sweep on toward the shore. The duck only bobs up and down, staying over the same patch of pond.
Something clearly travels to the shore, and the duck clearly does not. This lesson says exactly what a wave moves, and what it leaves in place.
Watch one thing at a time. The ripple pattern travels: each ripple ridge moves steadily toward the shore.
Now watch the duck, riding one patch of water. It rises, falls, and rises again, always over the same spot.
The duck shows what the water under it is doing. Each bit of the pond's water only oscillates about its rest position as the ripples pass.
Yet the ripples arrive at the shore with something real: they lift floating leaves there and slap the bank. Energy arrives.
In earlier grades, you saw that waves move energy without carrying the material along. Here is the particle picture behind that.
The pond keeps its water. The shore gets the energy.
Beata ties a ribbon to the middle of a long rope and sends waves along it from one end. What does the ribbon do while the waves travel the rope's full length?
The ribbon rides one particle's patch of rope.
Each particle of the medium only oscillates about its rest position and is not carried along.
The ribbon swings up and down about its own spot while the waves travel past it to the far end. It is not carried down the rope.
Far out on a lake, a speedboat passes. Minutes later, its wake reaches a drifting canoe and rocks it hard. What traveled from the boat's path to the canoe?
The canoe is rocked: energy arrived.
The water along the way only oscillated about its rest positions; it was not carried across the lake.
Energy traveled from the boat's path to the canoe through the water. The water itself stayed, bit by bit, near its own rest positions.
Ripples from a splash reach a toy sailboat across a pool and set it rocking. What traveled from the splash to the boat?
Cosmo watches waves crossing a harbor. He says: 'These waves carry the harbor water along with them toward the beach.' Is Cosmo correct?
Anselm sends waves along a backyard rope with a spot of paint at its middle. Beata says: 'The paint spot will stay near its own place while the waves pass.' Is Beata correct?
Which statement about a wave traveling through a medium is correct?
A wave travels left to right across a wave pool. How does a bit of foam resting on the surface move as the wave passes?
Ripples spread from where a kingfisher dove into a pond. Moments later, a lily pad near the far edge bobs. Which statement explains the bobbing?