Science Focus Topic 7 Notes: Stable Structures | Print |
The collapse of a structure can occur when the external forces cause the structure to become unbalanced. To design stable structures, engineers need to know what features of a leaning object determine whether it will tip over or stay balanced.

Center of Gravity
Engineers need to locate the center of gravity of a structure in order to stabilize the structure. The center of gravity is the specific point where all of the mass of the structure is evenly distributed around. The force of gravity acts on all parts of the structure and if all parts are evenly distributed around the center of gravity, then the structure will be stable.
Try this Virtual Lab

Unbalanced Structures
By locating the structure's center of gravity, an engineer can tell if the structure is stable or unbalanced. (figures 4.64A and 4.64B)

Firm Foundation
The foundation upon which the structure is built must be stable, especially if it is moist, otherwise the compressive forces may cause the structure to tip and become unstable. If engineers and builders do not take into account the soil type and formations, the structures built may experience cracks in their foundations and walls.
Foundations can be constructed on
solid bedrock, or, pilings (large metal, concrete or wood cylinders) can be used, if the layers of soil above the bedrock are loose enough. Some lightweight structures do not have to rest on the bedrock or, have to have a foundation that goes down very deep, because the ground doesn't freeze.

A road base is made up of layers (
figure 4.68B)

The load of the structure can be spread out over a large area (footings help to do this -
figure 4.68C)

Rapid Rotation
Speed helps to increase stability.


Spin stabilization, the principle with which the gyroscope works, is especially useful for objects that do not rest on a solid foundation.

Check out some crazy Amusement Rides

the Gravity Ejection Ride (Reverse Bungee)

and the Gyro Ride