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Extension and compression springs are literally on opposite sides of the spring spectrum. Extension springs are used primarily to hold two components together, while compression springs are best for keeping components from meeting in the first place. Both employ a coil design for elasticity and strength, but they work under two different principles of elastic potential energy.
An extension spring is usually made from smaller gauge wire and wound very tightly. Both ends may have loops or hooks for attachment purposes. The springs on a child's trampoline are prime examples of extension springs in action. Each spring is attached to a section of canvas and the metal support frame. Without a load, the extension springs remain compact and unstretched. As the child jumps on the canvas, the individual springs receive portions of the load and the coils stretch out.
At this point, when the coils are stretched to their limits, the spring contains the most potential energy. When the springs return forcefully to their original positions, all of that energy is released and the child is thrown into the air. This is the primary function of an extension spring, allowing an outside force to create tension but then using potential energy to pull the components back together. The worst damage an extension spring can sustain is a stretch past its natural limits. Once the coils of an extension spring are damaged, it cannot return to its original state of tension. Extension springs usually have rings or loops on each end to make it easier to connect to the components.
Compression springs are designed to work differently. They are generally made out of larger gauge wire and are not wound in tight coils. Compression springs may have rings on each end which support their loads. A child's pogo stick or a car's shock absorber are both examples of compression spring technology. The spring is naturally at rest when in an extended position. As the child jumps on the pogo stick, the spring inside the toy is pushed down. The child can only apply a certain amount of force to the spring, so it will only contain a similar amount of potential energy. The compression spring contains the most potential energy when it has been pushed together. The spring returns to its natural position, releasing its energy along the way. The child is propelled into the air from this recoiling action.
One smaller example of a compression spring is called a Belleville spring or Belleville washer. The washer is actually a disk with a distinctively curved center. As force is applied to the washer, it begins to flatten out and become stronger. Engineers often use Belleville springs in various combinations to duplicate the qualities of other spring systems. These washers are often used whenever two parts of a machine need to be suspended or protected from unnecessary shock, for example.
Compression springs can also be found in mattresses and earthquake-resistant foundations. The main problem compression springs face is the possibility of flexing under pressure. If a compression spring receives an uneven load, the coils may bow out and fail. For this reason, many compression springs are protected with flexible but firm boot covers made from rubber, cloth or plastic. In order to avoid major failures, the overall length of a compression spring must be considered. The length of a compression spring must be controlled (if it is not guided) to ensure that it does not buckle or flex-out. Compression springs usually have flat-ground ends so that they are parallel with eachother ensure even forces throughout the stroke.
Extension and compression springs may have different applications, but each demonstrates the usefulness of potential energy and the many uses of a coil design.