Originally Posted By: paul

I thought you could just imagine them sliding on a support.


OK. Those 4 sliding supports together carry the entire load applied by the mass. All 4000N, and they apply that to the pipe, pushing it backwards.

There's no "law of conservation of magnitude of force". You can't convert a 4000N longitudinal force to 4 x 1000N lateral forces. Sure you can get 4 x 1000N lateral forces using that mechanism, or you can get 1,000,000N laterally if you want. Either way it doesn't reduce the 4000N longitudinal component.