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# External and internal forces - PowerPoint PPT Presentation

External and internal forces. There are TWO types of forces that designers MUST consider when designing structures. External Forces: forces that act on a structure from the OUTSIDE Internal Forces: forces that act a structure from WITHIN. External forces.

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## PowerPoint Slideshow about 'External and internal forces' - nimrod

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Presentation Transcript

• There are TWO types of forces that designers MUST consider when designing structures.

• External Forces: forces that act on a structure from the OUTSIDE

• Internal Forces: forces that act a structure from WITHIN

• What are some external forces you can think of?

• The most obvious external force is gravity

• External forces occur when……..

• You push a swing, pull an elastic or throw a ball

• External forces on buildings include…..

• Wind, earthquakes, weight of people on the floors of the building and the weight of the building itself

POINT OF APPLICATION:

The precise point at which the force is applied

PLANE OF APPLICATION:

An imaginary flat surface through which an applied force passes

****the point and plane of application make a difference in how an applied force affects a structure. See page 278 in your text

• Tension

• Examples include: a stretched skipping rope, a trampoline, an electrical power line, a guitar string, the cables of a suspension bridge

• Once the particles pass their breaking point the objects are unable to return to their original shape

• Compression

• Examples include: kicking a soccer ball, step on the sole of your shoe, lay your head on a foam cushion.

• Torsion

• Examples include: when a skater twists in a jump, a washcloth is wrung out, a doorknob is turned.

• Created when both ends of a structure are twisted or when one end is twisted and the other is left stationary

• Shear

• Examples include: scissors cutting paper, strong wind bending a tree

The force acting within the rope is called?

shear torsion tension compression