Fire Hoses

Nozzles greatly increase the force that can be produced by water flowing through a hose. As shown in part a and b in Figure 1. This is how fire hoses get the high pressure flows required to effectively extinguish fires in hard to reach places.

Figure 1 - Diagram of force exerted on a hose - (Vera, Rivera and Núñez, 2014)

Figure 2 - Video of fire hoses lifting a car - (Viral Generation Republic, 2016)

As shown in this video Figure 2 (skip to 45 seconds) hoses can be very powerful. A few of them together can lift a car! You may think this lift is due to Newton's third law meaning the forward force of the water on the ground has an equal and opposite reaction force that pushes the car up. However, as explained in this journal on Backward Reaction Force on a Fire Hose (Vera, Rivera and Núñez, 2014), if the hose is straight, although there is a reaction force this stretches the hose instead of putting any force into the car. But as you can see these hoses have large bends in them. The change of momentum of water direction as it hits these bends causes then downwards force as shown in part c and d of Figure 1.

References:

Vera, F., Rivera, R. and Núñez, C. (2014). Backward Reaction Force on a Fire Hose, Myth or Reality?. Fire Technology, 51(5), pp.1023-1027. (Attached below)

Viral Generation Republic (2016). Firefighters lift car using fire hoses. [video] Available at: https://www.youtube.com/watch?v=xk_5nl3_mGI [Accessed 18 Mar. 2019].