Internal and
External Forces
·
External force: acts on an object from outside the object; e.g., wind, gravity,
earthquakes
o Gravity
§ is a natural force of attraction
§ acts on all structures all the time
§ pulls structures towards Earth’s centre
·
other external forces
o a person on a ladder
o pulling a drawer open
o sitting on a chair
o cars on a bridge
o wind/snow/rain
·
Internal force: one part of a structure acting on another part of a
structure; e.g.,
o tension in stretched cables on a bridge
o compression by the weight of a roof on the walls
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