I just moved to a Nikon D7100. On my previous camera (D40X), I used to be able to press playback, then use the aperture/speed dial/wheel to scroll quickly through pictures in playback mode. I can't figure out how to do it on the D7100 (my friend has a D7000 and it works perfectly on his). On mine, when I scroll, nothing happens.. Do you know how to on this model?
On the back of the camera, there is a dial like this:
Use the arrows to scroll back and forth through your images, after pressing the playback button. You can press up/down to scroll through additional information about an image (view histogram etc)
This is on page 35 of your manual
Edit: on page 257 of the manual, it says about custom menu f5 (Customize Command Dials): if it is set to Off, then the multi-selector (that I described above) is used to scroll through images. If set to On, then the aperture dial can be used.
So try going into custom menu, item f5 to On, and it may work as you expected. It has other side effects which you can read in the manual