15 20 25 30 35 40 50 55 60 63 70 80 90mm silicone pvc plastic vacuum suction cups sucker with plastic 30mm flat top sucker

15 20 25 30 35 40 50 55 60 63 70 80 90mm silicone pvc plastic vacuum suction cups sucker with plastic metal hook M4 M5 screw  30mm flat top sucker  

A suction cup, also sometimes known as a sucker, is an object that uses negative fluid pressure of air or water to adhere to nonporous surfaces and in the process creates a partial vacuum.^[1] They exist both as artificially created devices, and as anatomical traits of some animals such as octopi and squid.

Vacuum

The concept that's most important, and what makes a suction cup's bond strong, is the creation of a vacuum. 

When a suction cup is pressed against a surface, it pushes out all of the air beneath it and creates a vacuum 

between the cup and the surface. This vacuum holds the suction cup tightly, and it will continue to do so until 

the pressure on the outside of the cup becomes lower than the pressure on the inside of the cup.

The working face of the suction cup has a curved surface. When the center of the suction cup is pressed against a flat, non-porous surface, the volume of the space between the suction cup and the flat surface is reduced, which causes the fluid between the cup and the surface to be expelled past the rim of the

circular cup. When the user ceases to apply physical pressure to the centre of the outside of the cup, the elastic substance of which the cup is made tends to resume its original, curved shape. Because most of the fluid has already been forced out of the inside of the cup, the cavity which tends to develop between the cup and the flat surface has little to no air or water in it, and therefore lacks pressure. The pressure difference between the atmosphere on the outside of the cup, and the low-pressure cavity on the inside of the cup, is what keeps the cup adhered to the surface.

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