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External and internal forces

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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External and internal forces

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  1. 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

  2. External forces • 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

  3. Important things about external forces 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

  4. Internal forces

  5. Examples of the 4 internal forces • 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. • Compressed objects usually return to their original shape

  6. Examples continued • 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

  7. What do you remember? The force acting within the rope is called? shear torsion tension compression

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