(Title Image: http://www.defenders.org/sites/default/files/styles/large/public/dolphin-kristian-sekulic-isp.jpg)

By Laurin Fisher
For Physics 212x
On 4-13-15

HYDROPLANING

Let me explain hydroplaning a bit more in general before I get to how a dolphin does it.

Hydroplaning (for us humans) usually occurs in a car on an intensely rainy day. The rain water covers the road and the car's tires are no longer making contact with the road but are busy trying to move all the water out of the way. The driver no longer has control over their vehicle because there is no friction. Hold up, maybe I should start at how a car moves in the first place.

BASIC PHYSICS
I'm not going to go into too much detail here, but basically all things that move have forces acting on them and each force on an object has an equal and opposite reaction force. For example the car below is driving down a highway.

The driving force in this picture is the car's engine pushing it forward with the tires.The tires are pushing on the ground backward and the ground, in turn, is pushing the tires forward. Thus the car moves forward and the ground (ever so slightly) is pushed backwards, but humans can't really tell. Thus the forces are equal and opposite.

Since you know how a car moves now let's get back to hydroplaning.

As you saw above a car is dependent on friction to move. The tires have to make contact with the ground and since friction is the irregularity of objects on the molecular level (think jagged peaks) when the ground is instead replaced with a puddle of deep water, the tires are no longer in control. The tires are not able to push enough water out of the way to move in a directed path by the driver. It is like driving on a sheet of ice. The car is out of control and water is splashing everywhere.

Now if this is the case with cars- why do dolphins hydroplane? How do they hydroplane in the first place?

Perhaps you'd be surprised to know that dolphins have been caught hydroplaning on camera. Or perhaps your not surprised at all. But besides the point, they have, and they use it as a technique to hunt small fish in shallow areas.

As you can already tell there is a big difference between dolphin hydroplaning and car hydroplaning. Cars need deep water but dolphins need shallow water. However how it happens is the same, water is between the object/animal and the surface.

Here's a video on dolphins hydroplaning, take a look and see how they use it to their advantage.

(video of Dolphins Hydroplaning https://www.youtube.com/watch?v=o6yzpe8r4xg)

There is a danger for the dolphins when they hydroplane. They have a chance of becoming beached and beached is death for almost every sea animal. So how do they do it? First, let's look at the forces acting on a dolphin using the spherical cow method (pretending the dolphin is just a dot rather than having multiple components with different surface areas).

(picture slightly modified, originally from http://www.clipartlord.com/category/animals-clip-art/sea-creatures-clip-art/page/8/)

Of course gravity is always in there.

Dolphins move their tail up and down rapidly, picking up speed in order to hyrdoplane (speed is essential for hydroplaning with cars as well). Then they go into the shallow water where the smaller fish are and grab them as they speed by. The layer of water between the dolphins skin and the surface allows the dolphin to slide by as if on ice, and can get beached just as easily by losing control on the "ice". After all fins aren't really made for land.

SS

Here are some fun links here on the bottom. If you want to know more about dolphins click on the links. (Or if you want to see some more awesome dolphin photos for that matter.)