describe how the input force,outforce and fulcrum should be arranged so that a child can lift an adult using his own body weight on a seesaw.

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Law of the Lever The figure shows a lever system, similar to a seesaw that you might find in a children's playground. For the system to balance, the product of the weight and its distance from the fulcrum must be the same on each side: that is,

This equation is called the law of the lever and was first discovered by Archimedes (see page 787).

A woman and her son are playing on a seesaw. The boy is at one end, 8 ft from the fulcrum. If the son weighs 100 lb and the mother weighs 125 lb. where should the woman sit so that the seesaw is balanced?

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Learning Goal: To make the connection between the intuitive understanding of a seesaw and the standard formalism for torque. This problem deals with the concept of torque, the "twist" that an off-center force applies to a body that tends to make it rotate. (Figure 1)

(a) Marcel is helping his two children, Jacques and Gilles, to balance on a seesaw so that they will be able to make it tilt back and forth without the heavier child, Jacques, simply sinking to the ground. Given that Jacques, whose weight is W, is sitting at distance to the left of the pivot, at what distance should Marcel place Gilles, whose weight is, to the right of the pivot to balance the seesaw?

(b) Find the torque about the pivot due to the weight w of Gilles on the seesaw.

Express your answer in terms of L1 and w.

(c)Determine the sum of the torques on the seesaw.

(d) Gilles has an identical twin, Jean, also of weight. The two twins now sit on the same side of the seesaw, with Gilles at distance from the pivot and Jean at distance. w L2 L3 Where should Marcel position Jacques to balance the seesaw?

(e) When Marcel finds the distance from the previous part, it turns out to be greater than, the distance from the pivot to the end of the seesaw. Hence, even with Jacques at the very end of the seesaw, the twins Gilles and Jean exert more torque than Jacques does. Marcel now elects to balance the seesaw by pushing sideways on an ornament (shown in red) that is at a height above the pivot.