See-Saw

   At one point in your life you probably have seen or been on a see-saw. If you haven't, take my advice they are so much fun!!! Thinking about that, why are they so much fun? I'll tell you why.

   A see-saw is actually a lever.

A lever is a device consisting of a bar turning about a fixed point. The pivot point on the see-saw is in the middle of the board.

In a rotational motion, the see-saw shifts around this pivot point. Torque is the force that acts to produce rotation. Torque can begin, halt, or change the direction of the rotation of the see-saw. When there is no net torque, the see-saw is balanced. For a balanced see-saw, the formula is:

(m1) (g) (d1) = (m2) (g) (d2)

m1 = the mass of the first person

d1 = distance the first person is from the pivot point

m2 = the mass of the second person

d2 = distance the second person is from the pivot point

g = -9.8 m/s/s

Let's try an example:

Sue and Lily are on a see-saw. Sue is 73kg and is 2.3m away from the center of the see-saw. Lily is 3.1m away. The see-saw is balanced. How much does Lily weigh?

m1 = 73kg

d1 = 2.3m

m1 = ?

d2 = 3.1m

g = 9.80m/s² weight.

   *Since we know the see-saw is balanced, we can find Lily's weight. We'll use (N) as the unknown weight.

(73kg) (9.80m/s²) (2.3m) = (N) (9.80m/s²) (3.1m)

1622.88 = 30.38(N)

N = 53.42kg

Knowing this, you must be asking yourself, how do people of different masses equal out? Each person gives equal amount of torque but in the opposite direction. Keep in mind, each person would probably be a different distance away from the center (pivot point) of the see-saw. For the see-saw to work, the heavier person should be closer to the center (pivot point) of the see-saw, and the lighter person should be near the end or farther away. The force of each person pushing off the ground creates torque, which allows the see-saw to move up and down. The greater the force you apply the greater the up and down movement becomes and the higher or lower you go.

Here is an illistated example: