# Compression (physics)

In physics and mechanics, compression refers to a physical force that exerts pressure on an object, leading it to be compressed or pressed inward, resulting in a reduction of its size or volume. For instance, when force is applied to a gas-filled balloon, the gas molecules are compressed, causing the balloon to shrink. Compression stands in contrast to tension, where materials elongate or stretch due to outward forces. A practical comparison can be drawn between a coiled spring being compressed and a taut string experiencing tension.

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## Examples

### Shoe sole

When an individual walks or runs on the ground, the shoe soles experience the effects of compression. With each step, the force generated by the person’s body weight is distributed onto the shoe soles. This pressure causes the material of the soles to compress, meaning it is squeezed or pressed inward. As a result of compression, the shoe soles undergo a reduction in their volume or thickness. The principle of compression in shoe soles is vital for providing cushioning and support during walking or running activities, ensuring a comfortable and efficient experience while minimizing the impact on the feet and lower limbs.

### Hydraulic press

A hydraulic press showcases compression by exerting a crushing force on materials positioned within it. When activated, the hydraulic press generates a robust compression force that acts upon the material, leading to its deformation or crushing. This force is achieved through the transmission of hydraulic pressure, which presses the material inward, causing a reduction in its dimensions. Hydraulic presses find wide-ranging applications across industries, including metal forming, material testing, and precision force application in industrial processes.

### Spring

When the train moves, the springs fixed in its wheels undergo compression. This compression occurs when the train encounters uneven tracks or changes in speed, causing the springs to be squeezed. This squeezing action helps the springs absorb shocks, like bumps along the way, resulting in a smoother ride experience for passengers and cargo. Beyond just a smoother ride, this compression plays a significant role in maintaining the train’s stability; it reduces wear and tear on the train and tracks and ultimately enhances safety and comfort during train travel.

### Sponge

When a sponge is pressed by hand, it experiences compression. The force applied by the hand compresses the sponge, resulting in a temporary deformation of its shape. Once the external pressure is removed, the sponge regains its initial form due to its inherent elasticity. This elastic property allows sponges to be compressed and subsequently return to their original shape, showcasing the concept of compression in action.

### Bicycle seat

When a person sits on a bicycle seat, the springs fixed within the seat undergo compression. The weight of the individual applies a downward force on the springs, causing them to compress and reduce in height. This compression of the springs absorbs and distributes the weight, providing a cushioning effect that enhances comfort for the rider. The compressed springs ensure that the bicycle seat can adapt to the rider’s weight and movements, and help to minimize discomfort during rides over uneven surfaces or bumpy terrain.

### Bicycle pump

When the handle of a bicycle pump is pushed down, the air inside the pump’s cylinder is compressed. This means the air is squeezed into a smaller space. As the air is compressed, its pressure increases significantly. This high-pressure air is then forced through a valve and into the tire, causing it to inflate. This process exemplifies the concept of compression, where a substance (in this case, air) is subjected to force, reducing its volume and increasing its pressure.

### Suspension bridge

When a vehicle crosses a suspension bridge, the bridge itself experiences compression. The weight of the vehicle applies downward force to the bridge’s deck, resulting in compression within the bridge’s supporting components, including beams and columns. This compression counteracts the load and maintains the overall stability and structural integrity of the bridge. Suspension bridges are specifically designed and constructed to withstand these compression forces, enabling them to support the weight and movement of vehicles such as cars, trucks, and other forms of transportation. This design feature ensures secure and efficient passage for vehicular traffic across various spans and distances.

### Mattress

The spring fixed in a mattress undergoes compression as weight is applied to the mattress, such as when an individual sits or rests on it. This compression occurs because the spring is compressed under the downward force exerted by the weight of the body. The spring’s ability to compress and store potential energy not only provides cushioning and support but also enhances the comfort and resilience of the mattress. The phenomenon of compression within the spring improves the mattress’s ability to adapt to varying weights and positions, ensuring a more comfortable and restful sleep experience.