Lesson 6 disc.docx - Lesson 6 Horse and Sled This is a very old physics brain-teaser A horse is pulling a wooden sled across the ground According to

# Lesson 6 disc.docx - Lesson 6 Horse and Sled This is a very...

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Lesson 6: Horse and Sled This is a very old physics brain-teaser: A horse is pulling a wooden sled across the ground. According to Newton’s third law of motion, the force of the horse acting on the sled pulling it forward must be equal and opposite to the force of the sled pulling backward on the horse. According to Newton’s second law of motion, only net forces cause accelerations. Since the two forces must add to zero by the third law, the acceleration of the horse and sled must also be zero. So how can the sled ever move, much less accelerate? Make an initial posting before replying to other threads. To show this we must use two systems, the sled and the horse. The sled has two forces acting on it, the forward force from the horse and the backward force from friction on the ground. The two forces will be equal in magnitude at a constant velocity and a=0. The horse has a backward force from the sled and a forward force from the ground. These forces will have the same magnitude at rest or at a