What Newton Knew

Written By: Jean Emery - July• 29•11

 Were you one of those people who sat through high school physics doodling on your notebook, checking the clock above the classroom door every few minutes waiting for the bell to ring, wondering  when in the world you would ever use this stuff?

Surprise.  Now that you are playing agility, you are encountering the direct application of those long-forgotten–or maybe never learned?–physics lessons.

A Body in Motion . . .

Agility is all about physics (and that other titillating high school course geometry).  The lack of respect for the principles of physics and geometry or the recognition that such forces are at play in the game are at the root of many challenges encountered unnecessarily by novice handlers.

Take this simple seven jump sequence. 


Many novice handlers fail to take into account Newton’s laws of motion, particularly the laws related to centrifugal force, in choosing which side to lead out on.  In fact, based on what I’ve seen, deciding whether one side or the other is a better handling choice is often not factored into the handler’s planning. 

Real Life Lessons

Let me illustrate with the following video.

What my video stand-in (let’s call her Lucy) failed to take into account in planning her handling position was that moving bodies tend to continue forward in straight lines.  But, as you know, most agility courses are not composed of straight lines, but rather arcs and curves!

If you have never thought about agility courses this way, you may have found yourself in situations similar to the one on the video.  Perhaps you and your dog have never actually collided, but you may frequently intrude on your dog’s path, forcing the dog to alter its path (maybe unexpectedly), shorten its stride, pull up and drop a bar.  The sensitive or polite dog may come to worry about the potential bad manners of colliding with its handler and try to find a solution by either slowing down or moving off the handler to put some distance between itself and the handler.  This might mean the dog actually runs by a jump or an obstacle because it is thinking more about avoiding a collision than finding the obstacle.

So if this sounds familiar, how do you avoid making this handling mistake?

First, ask yourself this question when deciding how to handle a course or exercise: are you choosing to run on the outside of the curve formed by the obstacles or the inside

The Hub and Rim Approach

The curve I am talking about is different from the dog’s path, although they are closely related.  Rather, think about the arcs that are created by centrifugal force when a moving body (our dog) travels from one obstacle to another. 

Now take a course map and look for arcs connecting a sequence of obstacles.  Sometimes this arc may be only two obstacles long, before it turns and arcs in a new direction.  Other times, like in a novice jumpers course, it could be seven to 10 obstacles long if the sequence forms one big jump circle

Here I’ve taken our seven jump sequence and found three arcs: the first I’ve highlighted in pink, the second in green and the third in yellow. 

 I have extended the arcs into full circles or ovals to help you visualize better the propulsive effect going on.  To emphasize the law of motion I have drawn arrows on the inside of each arc indicating the direction in which Newton’s law of centrifugal force will be acting. 

Now you can see why Dawg and Lucy collided in our video demonstration when Lucy choose to run around the right side of jump 2.  Centrifugal force was pushing Dawg into Lucy while Lucy was pushing Dawg away from her.

Almost always the better choice is to position yourself to the inside of the curve and the dog on the outside.  Think of the arc like a wheel with you at the hub and the dog on the rim.  You’ll avoid collisions this way.  Importantly, the dog can see the path it needs to follow and you at the same time because you will be along the direction of travel.  Compare to when the handler is on the outside of the curve.  Then the dog has to look back and forth from handler to path to get the information it needs.

Also, most dogs are faster than their handlers, so making the dog run the longer path and you take the shorter inside one is a smart choice.

 In a Future Post

I’ll expand on this hub and rim approach in part two of What Newton Knew to show you how you can plan your handling for an entire course using “arc analysis.”  A side benefit of this arc- sleuthing approach is that it can tell you where to put a side change, something that often puzzles new handlers.  Stay tuned.

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3 Comments

  1. Sharon Normandin says:

    Excellent analysis! Disagree a bit with including 1-2 and 5-6 as “arcs”; I see them as straight lines, but still a great way to illustrate things, especially for novice handlers. Thank you!

  2. James Bell says:

    Love love love the physics description applied to agility, so I’ll even let the centrifugal force vice inertia thing pass. :-)

    This really sets up the discussion of where to change sides as relating to the inflection points of those arcs, something I’ve taught to Chollas students for years, although with different language. Front cross before inflection points, rear crosses after inflection points.

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