MASS Mass is defined as the amount of matter in an object. Mass and weight are two different things. Weight is the force of an object due to the earth s gravitational pull. Weight changes as the elevation gets higher because the object gets farther away from earth. Mass however does not change, no matter where you are, because it measures the amount of matter in an object.
Compression is the force that s acts to shorten or compress the object it is acting on.
For example when you lay thin slab of wood across two chairs and then add force, the bridge will bend causing it to shorten in length. Tension is the force which lengthens or expands what it s acting on. For example when you lay a board across two chairs, just like with compression, when you apply force the bridge expands underneath. It also makes the sides of the board resting on the chair begin to lift up. There is much to learn about bridges before you can actually start designing them safely.