The Science of Water Slides

by Deb on September 29, 2009

We’re in Darwin, and no visit is complete without time at Leanyer Recreation Park, an amazing free water park with pools, slides, and all sorts of water play.

water park

They now have 3 big water slides as well, so since my husband and I took it in turns to have a go here it is: The science of water slides.

Gravity –What pulls you down!  On a slide you have potential energy from your position at the top and your potential to be pulled down.  It depends on gravity, your mass (plus the mass of water with you), and the height of the slide.  Seeing these slides all leave from the same platform they have the same height, therefore they have the same energy.  But they are different lengths.  So you have to travel shorter or longer distances with the same amount of energy – this translates to speed!  A short slide will be steeper and go faster.

Friction – What holds you back!  Friction is the stickiness caused by minute bumps on you and the slide.  There are two main ways water slides reduce friction:

  • Lubrication – all that water going down with you creates a film between you and the slide and stops the bumps from catching.
  • Decreased surface area – the less surface you have touching the slide, the less bumps there are to stick.  Remember it’s your mass that determines your speed and to go fast you want the smallest surface area touching the tube for your mass, so shoulders and legs.  Generally, Dad wins.

Inertia – This is what makes you go up the sides, NOT centrifugal force.  Centrifugal force is the one we all know about that pushes you out when you are going around and around, right?  Sorry, it doesn’t exist.  What is really happening is about inertia.  Inertia is the thing that makes it hard to start moving, or once you are moving makes it hard to stop or change direction.  It is the changing direction that is important when you are going around.  Your body ‘wants’ to continue in a straight line but you can’t, in this case because you are inside a curved tube.  So it feels like there is something pushing you out, even though there isn’t really.

So why do you go up?  Trying to go straight means you will go to the extreme outer edge.  In a round tube, the outer edge is up the side.  And of course once you are heading up, inertia will keep you going with the help of that lovely lubricating water.

The Slides

If you are in Darwin, the water park is an absolute must visit.  I didn’t get to do the red slide because it’s a tandem slide, but I found the blue to be marginally quicker but the corkscrews in the yellow more fun 😀

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