Where does thrust collide?

The forward reaction force that drives a vehicle, produced when an engine expels mass rearward and, by Newton's third law, is pushed forward in return: a jet engine or rocket accelerates air or exhaust backward and the equal and opposite reaction is the thrust. Anderson's 2016 Introduction to Flight derives it from the momentum given to the exhaust plus any pressure difference at the nozzle, so it is quoted in newtons and compared with a vehicle's weight as the thrust-to-weight ratio. The referent is a physical force acting on a body right now, not a fracture in the crust that took ages to form, nor a platform that reaches into a theatre audience.[1]

Unit

A propulsive force on a vehicle, quoted in newtons

Recovery means

Not applicable

Measured by

Measured directly on a test stand with a load cell, or computed from exhaust mass flow and velocity, and often reported as a thrust-to-weight ratio

A low-angle reverse fault along which horizontal squeezing pushes a slab of older rock up and over younger rock, stacking the crust and shortening it: the displaced slabs are thrust sheets, and where many stack together across a mountain front they build a fold-and-thrust belt. Boyer and Elliott's 1982 Thrust systems set out the geometry by which such faults join into imbricate fans and duplexes and mapped how the slices form in sequence. The referent is a fracture surface in solid rock, built slowly by compression over geological time, and it has nothing in common with a force pushing a rocket or a stage pushed toward an audience.[2]

Unit

A single low-angle fault surface carrying older rock over younger, scaled by its displacement

Recovery means

Not applicable

Measured by

Mapped in the field and in seismic sections by the offset of marker beds, the shallow dip of the fault, and the distance the upper block has travelled