Strength of Shapes!
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The shape of a structure affects
how strong it is. Rectangles,
arches, and triangles are the
most common shapes used to
build big structures.
To understand which shapes
should be used it is important to
know what forces act on them.
Forces in Tension and Compression
How do we define a force?
A force is a push or pull exerted by one object on
another.
A tensile force expands or
lengthens the object it is acting
on.
A compressive force
compresses or shortens
the object it is acting on.
Forces in Tension
and Compression
The rope is in tension
The stand is in compression.
Forces on Shapes
Engineers consider shapes under heavy loads when building large
structures.
Triangles are the only shapes that
cannot be deformed without changing
the length of one of its sides
Arches are strong because the force Shapes Lab (click here)
resulting from a heavy load placed at
Use the slider to apply
the top spreads down the sides to the weight to each shape
foundation.
and see how they react
A group of arches placed around a
central point creates a dome, which
distributes loads down through
curving sides to the foundation.
Bank of China Tower
Eiffel Tower
Centre Pompidou
Stansted Airport
Roman Colosseum
San Lorenzo, Florence
Musee d'Orsay
Iron Bridge at
Coalbrookdale
Suleyman Mosque
Florence Cathedral
Dome tent -poles bent into arches
with nylon fabric in tension.
Campo Volantin Footbridge - arch with
cables in tension
US Pavilion at Expo '67 - spherical
structure made of triangles
Psyclone Rollercoastertriangles in structure
Newton's Laws
When an object is at rest or moving with
a constant velocity, it will stay at rest or
moving with a constant velocity until is is
subjected to an unbalanced force.
To understand these forces we must first
define force.
How do we define force?
Newton's Laws
If an unbalanced force, F, is applied to
a mass, m, then the mass will
experience an acceleration, a.
F = ma
Newton's Laws
Every force of action between
objects has an equal, opposite, and
collinear reaction.
Basically, what is pushing down
must be pushing up if the object is
not accelerating!
If the object is not accelerating the
sum of all the forces must equal
zero.
Static Equilibrium
Static Equilibrium is the state of an
object when it is at rest or moving
with a constant velocity. There may
be several forces acting on the
object. If they are canceling each
other out the object is not
accelerating, then it is in a state of
static equilibrium.