I have noticed that schoolchildren are carrying ever increasing amounts of stuff with them (especially books, despite the one-laptop-per-child initiative). This can’t be good for a developing skeleton.
Today’s invention is therefore a schoolbag which has a handle hinged at one end. The handle requires that its sides be pressed together before the bag is lifted, in order to judge the strength of the user.
When next the bag is set down (detected by sensors within the base), the handle determines whether the bag has been carried for long enough to endanger the user’s joints. If so, the handle de-hinges for a preset period to give the user some time to recover.
The handle can also detect which hand is being used to lift the bag (by the relative pressure on each side) and thus can also encourage a change from left to right (by leaving the hinge open until the hand is changed).
Two such bags could even communicate wirelessly -to ensure eg that nearly equal loads had been placed in each.