You're probably not thinking about it when you're whizzing through one, but water slides are a great demonstration of the basics of physics.

Water slide designers, like Ray Smegal​, know they aren't able to harness the raw mechanical speed of a roller coaster in pursuit of fun.

So they very carefully manipulate physics to simulate a roller coaster's wild run at a much lower speed.

Mr Smegal, who likes to think of himself as something of a cross between a physicist and an orchestra conductor, has just put the finishing touches on the near-27-metre high, 186-metre-long Gravity Wave at Funfields Theme Park in Whittlesea.

​Mr Smegal, whose company is based in Canada but designs water slides around the world, describes a good slide as a "symphony" with multiple elements building to a powerful "crescendo".

The experience actually begins well before you hit the water; a well-designed water slide lets riders look out over the park as they climb the tower, reminding them that they are very, very high.

When the rider finally climbs into the tube, the Gravity Wave is designed to generate several physical forces in rapid succession. 

First, it swoops riders through a series of curves at speed.

When a moving body hits a curve, says Dr Joel Gilmore, physicist with the University of Queensland, two things happen.

"If you want to change direction, something has to push on you to change direction," Dr Gilmore said.

"Newton's law says that for every action there is an equal and opposite reaction. The wall is pushing you, and you're pushing the wall, and so you feel like you're being pressed against the wall.

"We call that G-force."

And then the floor drops out and you free fall.

This drop generates the highest speed on the ride, and produces a moment of weightlessness.

"Normally when you're standing on the ground, you've got the force of gravity pulling you down, and the floor is effectively pushing up on you," Dr Gilmore said. "Equal and opposite reaction, so you don't move. 

"But if you are in a free fall section, suddenly, all your body is accelerating at the same pace. What that means is we cannot feel gravity anymore."

The sensation of free fall is similar to the feeling of weightless astronauts experience in space – because, says Dr Gilmore, astronauts are in fact free-falling, rather than experiencing true weightlessness. "They are falling. It's just through the clever design of their orbits that they keep falling and missing the Earth."

At the bottom of the Wave's free fall section you hit a wall and slide up. This motion – an accelerating body hitting a wall and being forced to change direction – produces the G-forces that let you travel directly up the wall. 

"That section is designed to maintain the boat at the peak of the equator of that wall for as long as possible," says Mr Smegal.

"If you consider the vehicle sweeping across the top of the wall, as it hits max height and it's travelling across the feature, guests are nearly weightless.

"You feel like you are free-floating across the wall.                                 

"As guests move across, the radius of the wave decreases. So as gravity brings them back down the wall, it's like we're extending the length of the free fall."

A successful water slide, Mr Smegal says, should feel something like a good ski run.

"There are moments when you're very technical, you're hitting an edge. And sometimes you're just going really really fast."