Water exerts pressure on the walls of the pipes.
Explanation
The phenomenon is governed by the mechanical properties of fluids. Fluids (liquids and gases) exert force on the surfaces with which they are in contact. This force per unit area is defined as pressure.
Detailed Analysis:
- Water chemically reacts with the pipe material causing expansion. Incorrect: Water is generally chemically inert with respect to standard pipe materials (such as PVC, copper, or iron) in the short term. It does not react to cause rapid expansion or structural failure leading to gushing.
- Water exerts pressure on the walls of the pipes. Correct: A fundamental property of fluids is that they exert pressure in all directions against the walls of their container. In a supply pipe, the water is maintained at a pressure higher than the atmospheric pressure (either due to gravitational head or mechanical pumping). When a joint leaks, this internal pressure exerts an outward force, causing the water to gush out.
- The leaks create a vacuum that extracts water from the pipe. Incorrect: A vacuum implies a region of pressure significantly lower than atmospheric pressure. If a vacuum existed inside the pipe, air would be sucked in, rather than water gushing out.
- Gravitational force pulls the water sideways through the joints. Incorrect: Gravitational force acts vertically downwards towards the center of the Earth. While gravity is responsible for hydrostatic pressure, it does not pull water "sideways." The sideways ejection of water is due to the pressure acting perpendicular to the wall of the pipe at the point of the leak.
Key Takeaway:
Fluids exert pressure on the walls of the container they occupy. This pressure acts perpendicular to the surface and forces the fluid out if an opening is created.