See-saw, force exerted up by pivot?

• lizzyb
In summary, a child weighing 36 N climbs onto a see-saw that is 2.8 m long, weighs 11 N, and is tilted at an angle of 25 degrees from the horizontal. The see-saw is tied down with a rope at its left end and the center of its mass is directly above the pivot. The total positive force exerted upwards by the pivot can be calculated by finding the force that the rope exerts downwards on the see-saw, which is equal to the torque exerted by the child on one end of the see-saw (45.6779 N) multiplied by 2. This results in a total force of 127.3558 N.
lizzyb
see-saw, force exerted up by pivot?

A child weighing 36 N climbs onto the right end of a see-saw, little knowing that it is tired down with a rope at its left end. The see-saw is 2.8 m long, weighs 11 N, and is tilted at an angle of 25 degrees from the horizontal. The center of the mass of the see-saw is half way along its length and lies right above the pivot.

There are 5 questions total and I've sucesfully answered 4 of them so far yet this one is odd:

Q: What is the total positive force exerted upwards by the pivot?

I first tried simply adding the two weights together (47 N) but this was wrong; then I added the two forces regarding the torque plus the total weight of objects on the see saw (45.6779 *2 + 36 + 11), but again that was wrong. How do I put these together? thanx.

Is the right end of the seesaw touching the ground? If it was I would be inclined to say that only the weight of the seesaw is on the pivot.

lizzyb said:
I first tried simply adding the two weights together (47 N) but this was wrong; then I added the two forces regarding the torque plus the total weight of objects on the see saw (45.6779 *2 + 36 + 11), but again that was wrong. How do I put these together? thanx.

Please explain how you obtained 45.6779 *2. What you should try to calculate is the force that the rope exerts downwards on the see-saw. Can you take it from here?

thanks for the responses! the right end (with the child on it) is way up in the air and the rope is holding the left end on the ground.

I came up with 45.6779 * 2 because that is the torque the child exerts on the right hand side and the torque the rope applies (they're the same since they're in equilibrium).

oh I see! ok i'll try it.

great! thanks! I got it: (36 + 11 + 36 [the rope's force {not torque}])

45.6779 * 2. I don't think this is the actual torque, you must have got some calculations mixed up.

You're welcome. Good job in figuring it out.

1. How does a see-saw work?

A see-saw works by using the principle of leverage. When one end of the see-saw is pushed down, the other end will rise up due to the pivot, or fulcrum, in the middle.

2. What is the force exerted up by the pivot?

The force exerted up by the pivot is equal to the force exerted down on the other end of the see-saw. This is known as the law of action and reaction, or Newton's third law of motion.

3. How does the position of the pivot affect the see-saw?

The position of the pivot affects the see-saw by changing the balance of forces. If the pivot is closer to one end, that end will have less leverage and require more force to lift, while the other end will require less force to lift.

4. What factors can affect the force exerted up by the pivot?

The force exerted up by the pivot can be affected by the weight of the objects on each end of the see-saw, as well as the distance between the pivot and the objects. Additionally, the length of the see-saw and the angle at which it is pushed can also affect the force exerted up by the pivot.

5. How can a see-saw be used to demonstrate force and motion?

A see-saw can be used to demonstrate force and motion by showing how the force applied to one end can be transferred to the other end through the pivot. It also allows for the exploration of concepts such as balance, leverage, and Newton's laws of motion.

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