# Water cannon toy and pressure

I have this toy I bought for my daughter. It is called a Geyser Water Cannon and supposedly it works using the Venturi effect. Basically it's a 2 foot cone that starts out with a wide diameter (1 foot) and narrows to about 1 inch - with openings on each end. When you pull down or push down this cone on a surface of water - it can shoot water up to 30 feet.

I am all confused by this talk of the Venturi effect as water travels from a wide volume to a narrow one.

Questions:
1. Is the water shooting higher not created because I am pushing and concentrating water up a narrow channel and thus the pressure created shoots the water higher??

2. Doesn't a syringe work in the same way with the opening being smaller in diameter than the barrel of a syringe? And thus the stream shoots higher because of pressure?

Drakkith
Staff Emeritus
I don't think it's the Venturi effect. That has to do with a reduction in static pressure when a fluid passes through a constriction.

From the wiki article on the venturi effect: According to the laws governing fluid dynamics, a fluid's velocity must increase as it passes through a constriction to satisfy the principle of continuity, while its pressure must decrease to satisfy the principle of conservation of mechanical energy.

It looks to me like it's simply a result of the principle of continuity. So I think the answer to both of your questions is, yes.

If this isn't right someone correct me.

Bobbywhy
Gold Member
Here is an advertisement for the "Geyser Water Canon" with a photo of the device, plus many comments from users. This may help others describe the principle of operation.

http://www.yoyo.com/p/geyser-guys-geyser-gusher-water-cannon-colors-may-vary-354192 [Broken]

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@ Drakkith - thanks so much for the reply.

So the next query is, Given a set force and size of the cone (volume wise), we can can actually increase the pressure to almost any reasonable pressure (i.e. 500 Kpa?) by just making the tappering part more narrow and/or make the opening smaller correct?

Drakkith
Staff Emeritus
@ Drakkith - thanks so much for the reply.

So the next query is, Given a set force and size of the cone (volume wise), we can can actually increase the pressure to almost any reasonable pressure (i.e. 500 Kpa?) by just making the tappering part more narrow and/or make the opening smaller correct?

I want to say yes, as that would make sense to me, but I have no formal physics education so I can't be sure.

I want to say yes, as that would make sense to me, but I have no formal physics education so I can't be sure.

@ Drakkith - ok thanks for your efforts.

If anyone else has thoughts on this I would appreciate. Thank you in advance.