Loads
Distinguishing between Mass and Weight
Mass - is the quantity of matter in an object. It
can be measured using a balance or scale.
Common units of mass are grams and
kilograms.
Weight is the force of Earth's gravity acting on
an object. It is measured in Newtons (N).
The mass of an object remains the same
anywhere in the universe, but its weight can
change depending on its location.
Internal and External Forces
Loads
A structure must be able to withstand all of
the forces that act on it (wind, rain, weight on
object on top of it, etc). The force acting on
a structure is called the load.
To describe how a force is acting on a structure,
engineers talk about 3 main things:
Magnitude - The size of the force compared with the size
and weight of the object.
Direction - The direction the force is coming.
Point and Plane of Application - The point is the exact
location where the force meets the structures. The plane is
the side of the structure affected by the force.
Vector Despicable Me.mp4
External Forces
Every structure needs to support a load. There
are 2 types of loads:
Static Load - is the effect of gravity on a structure.
Dynamic Load - is the forces that move or change over
time.
The total load is the sum of the static and dynamic loa
Example Think of a bookcase. Its static load consists of the materials the
bookcase is made from. Gravity acts on these materials whether
there are books on the bookcase or not.
Its dynamic load is the books. The size of the load changes with
the number of books. The effect of the load also depends on
where the books are placed on the shelf.
A dynamic load is a load caused by forces
other than the force of gravity (ex. fast moving
water, high winds, baseball bat striking a ball,
car hitting a guardrail, etc.)
Load
Static Load
Dynamic Load
Loads put stress on structures. The structures
respond by stretching, compressing, twisting
and bending. If stress is severe enough, the
structure will collapse.
Tension - a force within a structure or part of a
structure that stretches or pulls.
When forces pull in
opposite directions, the
force of tension is created
in the structure. The object
responds by stretching.
Compression - a force within a structure or part
of a structure that squeezes or pushes
When forces push in opposite
directions, the force of
compression is created in a
structure. The object responds by
becoming smaller.
Torsion - a twisting force within a structure or
part of a structure created by applying opposite
rotational forces.
Wringing out wet
clothes.
Shear - When parallel forces acting in
opposite directions are at work on a part of a
structure, the part is said to be under shear.
Pulling stuck licorice apart or
cutting paper with scissors.