What makes a fluid move — and what makes it stay put?
Start with a drop of soap, then compare a cup on a window, water crossing a rim, and air carrying dust. Each example makes you ask where a pressure difference acts and which paths are open.
Follow one chamber as its volume changes. Valves make filling and dispensing happen along different paths.
The next connection: The pump uses a pressure difference to move liquid. A suction cup uses a pressure difference to hold still, without that repeating valve cycle.
A pressure difference can press a cup against a surface. The seal matters because leaking air can remove that difference.
The next connection: A seal keeps the cup attached. A siphon instead needs a continuous liquid path and a lower outlet; compare what must stay closed and what must remain open.
Trace a continuous liquid path from a higher reservoir to a lower outlet. The height difference sustains the flow after the path is filled.
The next connection: A siphon has a height difference to sustain its flow. A vacuum cleaner uses a powered fan to maintain moving air through an open path.
Follow the air through the inlet and filter toward the fan. A working flow path matters as much as the pressure difference.
Back to the question: Return to the trail and compare a seal that holds with a path that carries a fluid.
Keep the differences in view
Compare the cause.
These objects do not share one hidden mechanism. A pump changes chamber volume, a suction cup holds through a pressure difference, a siphon needs a continuous liquid path, and a cleaner maintains airflow with a fan.
Look for the boundary first. Then ask what maintains the pressure difference and where the fluid can go. A seal can hold an object; an open path can carry a flow.
Keep looking
A reason to return.
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