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Chapter 5: Problem 1

After you push a suction cup against a smooth wall, the elastic cup bends back and a small, empty space is created between the cup and the wall. What keeps the suction cup against the wall?

Short Answer

Expert verified
Atmospheric pressure pushes the suction cup against the wall by acting on the lower pressure in the vacuum created behind the cup.

Step by step solution

01

- Understanding the suction cup mechanism

A suction cup sticks to a smooth surface by creating a vacuum or low-pressure area between the inner surface of the cup and the wall. When you press it against the wall, air is pushed out from the space between the cup and the wall.
02

- Creation of vacuum

After pressing the cup, the elastic material of the suction cup tries to regain its original shape, which creates a small, empty space (a partial vacuum) between the cup and the wall.
03

- Atmospheric Pressure

The external atmospheric pressure is now greater than the pressure inside the vacuum space. The higher external atmospheric pressure pushes the cup against the wall, keeping it in place.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Vacuum Creation
When you press a suction cup against a smooth wall, you are essentially creating a low-pressure area. This happens because pressing the suction cup expels most of the air trapped between the cup and the wall. As the cup is made of an elastic material, it tries to return to its original shape once you stop pressing. This action leaves a small empty space - a partial vacuum - between the cup and the wall.

Why is this important?
  • The vacuum creates a difference in pressure between the inside of the cup and the outside environment.
  • This pressure difference is crucial for the suction cup to stick to the wall.
Understanding vacuum creation is the first step to comprehending how suction cups work. It's all about removing air to create a lower pressure area inside.
Atmospheric Pressure
Atmospheric pressure plays a vital role in the functioning of a suction cup. This is the force exerted by the weight of the air molecules around us. Once a vacuum is created inside the suction cup, the pressure inside is significantly lower than the pressure outside.

How does this help the suction cup stick?
  • The higher atmospheric pressure outside the cup pushes it against the wall.
  • This pressure is what makes the cup stay in place until enough air enters the vacuum to equalize the pressure.
When the atmospheric pressure outside is greater than the pressure inside the cup, it effectively pushes the cup onto the wall, keeping it firmly attached.

This concept helps to understand why suction cups may struggle to stick in lower atmospheric pressure environments, like at high altitudes.
Elasticity
Elasticity refers to the ability of a material to return to its original shape after being stretched or compressed. The silicone or rubber material of a suction cup is highly elastic.

How Elasticity Plays a Role:
  • When you press a suction cup against a wall, the elastic material temporarily deforms, pushing out air.
  • Once you release the pressure, the elastic cup tries to regain its shape, creating the vacuum inside.

The elastic property of the suction cup is crucial in maintaining the vacuum and ensuring that the cup sticks. Without this elasticity, the suction cup would simply stay deformed and fail to create the necessary low-pressure area for suction to occur. This explains why understanding elasticity is key to mastering how suction cups work.

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