Load Cells
A load cell is a specialized force sensor that is designed to measure a specific type of force acting upon it.
There are load cells to measure compression, tension and shear forces. For highly custom projects, you can attach tiny strain gauges to a material to measure specific forces acting on that member.
Load cells and strain gauges tend to output very low voltages, so most of them must be connected to a wheatstone bridge interface in order to be measured accurately.