The figure below shows a rubber sucker. Explain why the sucker sticks on a clean flat surface.
Answer Text: This is due to the difference in the atmospheric pressure. When the rubber sucker is pressed against a surface, all the air molecules inside the rubber cup escape out. Hence, fewer air molecules are left inside in the cup than they were before. Therefore, the pressure outside is more than the pressure inside. But the outside force is greater than the inside force because the outside pressure is greater than the inside pressure. Therefore, the net force on the rubber cup is directed towards the surface. The rubber cup is pushed against the surface and in return, the surface also applies a force on the cup and hence, the rubber sucker is at rest and sticks to the surface.
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