The important contrast is that rhythmn photographs suggest dynamism, leading the eye through the image, whereas pattern images are static.
I chose an image taken at the Champions League Final in May to demonstrate rhythmn:
The colours in the crowd appear from coloured card left on people's seats - these are raised over their heads to spell out a message and, also in this case, alternate between the red and blue of Barcelona's colours.
The rhythmn effect derives from the eye being lead to the right by the three banners on the pitch, the half written "football" leading off frame, and the curvature of the stadium.
A school exam room provided an ideal location for a photograph demonstrating pattern. This is most definitely static. The notes made clear that patterns should extend beyond the frame with no boundaries thus enabling the eye to see beyond them - this effect is enhanced in this image by the perspective induced from the camera's position.
This image taken at the Champions League Final demonstrates both pattern and rhythmn. The pitch lines created by the mower clearly are a pattern and extend way beyond the shot, whereas the umbrellas seem to be more of a rhythmn - there is no definite pattern, that came later in the first shot above when the girls arranged themselves on the pitch, but the eye roves along the row looking for more order than exists.
I partially desaturated this shot by extracting the green channel in order to emphasise the umbrellas; the pattern on the pitch was strong enough not to risk losing some of the rhythmn effect by having a dominating colour.
This was a very useful exercise making me think about how to photograph pattern and how to view rhythmn in one's images - what do I imagine my viewer is going to see and in what order? Stressed to me the importance of having empathy with the viewer.
