Question:

What is this video trying to show?

Answer:

The initial velocity of the water droplets reveals the direction of the pressure forces the water was exerting on the balloon surface just before the explosion. It reveals clearly that he pressure forces were acting perpendicular to the balloon surface AT EVERY POINT on the balloon surface.

Delving Deeper

We should be careful in distinguishing between PRESSURE and PRESSURE FORCES. Pressure desribes how compressed a point in a fluid is. Pressure force refers to the resulting force a fluid exerts at a point on the surface.

We often hear the expression that “pressure acts in all directions”. A more accurate statement would be “the pressure forces resulting from the pressure at a point acts in all directions.”. Pressure is a scalar quantiy. Strictly speaking, it (“acts in all directions” and therefore) has no direction. The pressure force, on the other hand, is a vector since it has a defined direction. That direction is always perpendicular to the surface.

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