One simple explanation and easy to draw for your students: The CG of
the glider is typically ahead of the "center of lift". An "up" gust
will cause nose to pitch down around the CG. Refer to "Aerodynamics
for Naval Aviators" for more details.

Be "one" with your glider. Feeling (and hearing) the slight airspeed
change is usually a faster indication of lift than your vario. So look
outside the cockpit to clear, pull and turn into the thermal core!

Burt
Marfa Gliders, west Texas USA
www.flygliders.com