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# Unit d - section 2.3 -- external forces

## on Mar 21, 2012

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## Unit d - section 2.3 -- external forcesPresentation Transcript

• Mr.Ilko
•  Internal Force – is a force that one part of the structure exerts onto another part of the same structure ◦ These are also known as forces that act within a structure ◦ EX. Press the palms of your hands against one another and push
•  There are three main forces that act within a structure You can classify them by the direction in which they within the object The three are; ◦ Compression ◦ Tension ◦ Shear
•  Is a force that acts to squeeze an object or push parts within an object together. Solid structures usually resist the force of compression due to the strong materials they are made from Structures with parts that must resist compression include the human body, chairs and shelves
•  Is a force that acts to stretch and pull apart something It can cause lengthening and possibly snapping of a component Structures that have parts that resist tension include ski lifts, hydro towers and running shoes
•  Is a force that acts to push parts that are in contact with each other in opposite directions Structures with parts that must resist shear include doors, airplanes, and scissors
•  When different kinds of internal forces act on a structure at the same time they are called complementary forces Bending is an example of this at work, both compression and tension are involved ◦ If the load is too great the beam may break By looking at were breaks occur, engineers can improve a structure