Why Does a Fire Hose Recoil When the Water Is Turned On?

The engine puts Newton's third law into action.

Sir Isaac Newton introduced his Laws of Motion in 1687. Newton's third law states, "For every action there is an equal and opposite reaction." A jet engine is a good example. Air drawn into the engine is forced out the rear. This force is the "action" in Newton's Law. The "reaction" is the jet being propelled down the runway and into the air.

Function

To stand, you must apply enough force to lift your body weight.

It doesn't matter if you're pushing or pulling, there is a force working against you. Someone weighing 110 pounds must overcome 110 pounds of gravity to stand up. That is Newton's third law. You must apply enough force (action) to overcome the 110 pounds working against you (reaction).

Significance

As water is being pushed out of the nozzle, drag and gravity are pushing back.

When doing work, according to Newton, there will always be a pair of forces at odds with one another, equal and opposite. The fire pump propels water at 150 psi. Water is pushed through the hose until it reaches the nozzle. The movement of the water is working against drag and gravity. As water exits the nozzle, drag and gravity are pushing back. This is the recoil felt by the firefighter.

Effects

The fire fighter is the mediator between these forces. The force of the water has overcome the forces working against it. It shoots out of the nozzle and is propelled in front of the fire fighter. If the fire fighter loses control and drops the hose, it will whip back and forth at the nozzle because of the equal and opposite effect.

References

• "Fire Tactics": Firefighting Nozzle Reaction: Paul Grimwood
• "The Physics Classroom": Newton's Third Law of Motion
• "Teachers' Domain": Newton's Third Law: Action - Reaction

Resources

• "How Stuff Works": How Newton's Laws of Motion Work