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How the Obstacle WorksHurdles are one of the simplest obstacles in dog agility. Running up to the the jump, the dog must leap from the ground over the hurdle. The dog must clear the entire jump, not knock off the poles of the hurdle or go under the jump. Usually about three hurdles appear in each agility course.
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Energy
When a dog (this dog happens to be Scruffy) is running on the ground, he has kinetic energy, which is the energy of motion. The equation for kinetic energy is ½*mass*velocity². Scruffy has no gravitational potential energy, which is energy an object has because of its height in a gravitational field, in this case Earth's gravitational field. The equation for gravitational potential energy is mass*g*height. Since Scruffy is running on the ground, and has not be lifted off the ground at all, his height would be zero, giving him zero potential energy. However, when Scruffy leaps into the air as he jumps the hurdle, Scruffy increases in height and in a parabolic shape he goes over the hurdle. As he goes up, his kinetic energy decreases (Scruffy's velocity is decreasing) as his potential energy increases (Scruffy's height is increasing). However, the Scruffy's total energy remains the same at all times throughout the jump because of the law of conservation of energy, which states that a system's total energy can not increase or decrease but is conserved. This means that if Scruffy's potential energy increases, his kinetic energy will decrease and vice versa in order to keep the same amount of total energy. When Scruffy is at the height of his jump over top of the hurdle, he has zero kinetic energy and only potential energy. If we look at the equations for kinetic and potential energy, we can see that Scruffy has zero kinetic energy because for a extremely small amount of time he stops in the air and has zero velocity and his potential energy has increased so much because Scruffy has increased in height. As Scruffy goes down on the other side of the hurdle towards the ground, the opposite happens from what happened as he jumped up. His potential energy will decrease and his kinetic energy will increase.
Newton's 3rd LawNewton's third law states that "For every force there is an equal force in the opposite direction." This law is displayed in a dog's jump over a hurdle. Dogs jump by first lifting the front of their bodies up by pushing down with their front feet and then pushing down with their hind legs to lift them into the air. When Scruffy first applies force downward against the ground with his front feet this lifts the front of his body off the ground, and then he pushes his back feet against the ground, applying force with a powerful shove, and this launches him into the air over the jump. Since Scruffy is applying this force downward against the ground, as stated in Newton's third law, the ground will apply an equal amount of force back at Scruffy, sending him flying through the air. In agility competitions, dogs must have strong and healthy legs in order for the dog to push hard enough to achieve jumping over the hurdle.
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This graph represents Scruffy's energy as he goes over the jump. Due to the conservation of energy, K (kinetic energy) decreases and U (potential energy) increases as Scruffy goes up and vice versa when Scruffy goes down. Scruffy's total energy (the black line) is the sum of the kinetic and potential energy and remains the same through out the jump.
When a dog jumps, it pushes against the ground first with its front feet then with its hind legs and is this force its applies to the ground is applied back to the dog but in the opposite direction.
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