Having trouble finding ways to keep your kids interested in math/physics?
Try using working models of bridges and cranes.
Here are a series
of videos explaining basic engineering principles, torque, center of gravity, overturning moment, applied trig etc.
I'll be posting videos on cranes, how to build a simple crane for under $20,
and lots of bridge videos including truss bridges, cantilever and lift bridges, tower cranes etc.
the tower crane