Definition and Theory
Applied forces are forces, such as a push or a pull, that act on the outside of an object. The ability for an object to resist these externally applied forces and remain static (not moving or breaking) is the result of an objects internal structure to resist these forces and in some cases external anchoring to a larger body. Three basic types of internal forces or stresses that keep a structure static are compression, tension and bending. Large structures such as towers, cranes and bridges are composed of many small internal structural members. These small internal structural members are primarily designed to translate loads into compression and tension and try to avoid bending. This is because bending generally uses more material (costing more) than tension or compression for a similar load and length.

Procedure

• Using an 1/8" x 1/8" x 12" piece of balsa wood, conceptually test tension, compression and bending as shown in the diagrams above.
  • Tension: Place both hands on each end of the piece and pull. DO NOT BREAK THE PIECE.
  • Compression: Place both hands on each end of the piece and push until the wood bows. DO NOT BREAK THE PIECE.
  • Bending: Place the piece over an 11.5" span and push down in the middle until the piece bends. DO NOT BREAK THE PIECE.
• Record your observations.
• Lookup the formal definition of tension, compression and bending in an encyclopedia or engineering mechanics book.
• Sketch several common objects in your classroom or school. Label the kinds of stresses that may occur in each part when loads are applied for proper use.
• Answer the questions in the lab.

Laboratory Worksheet