How a suction cup sticks

In the picture

1. 1Cup at rest: air inside and outside push equally
2. 2Strong air pressure from outside pressing down on the cup
3. 3Flattened rim sealed to the glass with no air underneath
4. 4A snail’s foot: many tiny suckers that can change shape

Examples

• A rubber hook that holds a towel on a bathroom tile
• A snail climbing up a wall or a window

Quiz: How a suction cup sticks (Age 12)

1. 1

   Why does a suction cup stay stuck to a window?

   • It pulls on the glass like a magnet
   • A sticky coating on its rim glues it
   • The air outside pushes it onto the glass
2. 2

   What happens when you press a suction cup flat against a surface?

   • The cup gets heavier and sinks onto the surface
   • Air is pushed out from under the cup, so only outside air presses on it
   • Extra air is pumped in under the cup
3. 3

   How does a snail cling to a surface?

   • With tiny hooks that dig into the surface
   • With many tiny suckers under its foot that can change shape
   • With one big suction cup that never changes shape

The answers, each with its explanation, are in the app. This quiz is free there while the lesson is in the free week.