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How the Obstacle WorksThe teeter totter, also sometimes called the see saw, is an obstacle in dog agility that (like a see saw on which children play) consists of a plank that rests on top of a fulcrum, or non-moving focal point. The dog must walk (or run, if he or she is an expert) up the teeter totter and go down the other side when the teeter totter tilts down to the other side. The dog must wait for the end of the teeter totter to touch the ground before running off the teeter totter.
"See-saw not touching the ground before the dog leaving, but after it begins to tilt, is a fly-off penalty" - United States Dog Agility Association |
Levers
IntroductionA teeter totter is a type of lever, which is a simple machine. A simple machine is a device that makes work easier (there is less force needed or the force is applied in a different direction). There are six different kinds of simple machines including pulleys, ramps, wheels, and, of course, levers. A lever consists of a flat surface resting on top of the fulcrum (the stationary point in the middle that the lever rests on). There are two forces acting on opposite sides of the fulcrum: the effort and the load. The effort is the force that acts on the lever (in dog agility, this is the dog’s weight). The load is the force acting on the opposite end that has to be overcome by the effort force (this is the other side of the teeter totter).
How They WorkMany levers are used to lift things and they can make things easier to lift because they increase the distance over which the force is applied. The same amount of work (which is equal to force*displacement) is done as lifting it without a lever, but because the distance is greater, the force has to be smaller. With the fulcrum exactly in the middle, there is no advantage since the distance to the fulcrum to each end is equal. This advantage is called mechanical advantage and is calculated by dividing the distance from the fulcrum to where the effort force is applied by the distance from the fulcrum to where the load is applied. The closer the load is to the fulcrum, the easier it is to lift the load.
Before the Dogs: How Does One Side Stay Down?Before the dog runs up the teeter totter, the teeter totter must be balanced so that one side is resting on the ground. This can be achieved by placing a weight on that side or by moving the fulcrum slightly closer to the opposite side. By moving the fulcrum closer that one side, it means that the other side has to put in less force to keep it balanced, but since the force is just the weight of the other side, it does not change and thus there is too much force on that one side and it falls to the ground. Increasing the mass of one side (by weighting it down) also increases the force on one side, and causes that side to touch the ground.
Scruffy and Patches: How Mass Affects the Teeter Totter In dog agility, the dog must lift the opposite end of the teeter totter (the load) in order to complete the obstacle. The dog’s weight acts as the effort force to perform this task. The mass of the dog completing the teeter totter affects how easily it can complete this task. A smaller dog (let’s call him Patches) has to walk farther out on the same teeter totter as a larger dog (let’s call him Scruffy) does. Because Patches has less mass, the force he puts on the teeter totter (his weight) [Weight or mass?] will be less. Since he can’t increase his mass, Patches has to move farther out in order to achieve a greater mechanical advantage (because the distance between him and the fulcrum will be greater there). Scruffy, on the other hand, exerts a greater force on the teeter totter, so he does not have to go out as far for the teeter totter to tilt towards the other side. This may make the teeter totter obstacle easier for Scruffy and give him an advantage (although the weave poles are easier for Patches).
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Look at Scruffy go! He's already tipped the teeter totter!
Poor Patches! He's already gone out so far but he can't get the teeter to totter!
Disclaimer: The teeter totters in these pictures may be set up differently, which could also have affected how hard it is for these dogs to tip the teeter totter. |