Seesaws are a classic childhood play structure. Children can spend hours jumping up and down, balancing partners, and even trying to jump over each other.
As adults, we know that a seesaw is balanced when the weight of the partners is equal and the platform is level. However, this was not always the case!
Prior to 1900, seesaws were not perfectly balanced. In fact, in some cases, a heavier child would sit lower than their lighter partner. How could this be?
It all has to do with what material makes up the platform of the seesaw. If it is wood, then it can be made thicker in one side to make it level. If it is stone or concrete, then one side can be made higher than the other to create the illusion of weight difference.
Calculate the mass of both children
To figure out how the seesaw balances, you need to calculate the mass of both children. In this case, the boy is 100 kilograms, or 220 pounds, and the girl is 30 kilograms, or 66 pounds.
Since the boy is three times as heavy as the girl, you need to put a child with twice the mass of the girl on the other end of the seesaw to balance it.
So if you put a child with 60 kilograms, or 132 pounds, on the other end of the seesaw, it will be balanced. You can use either a boy or a girl with that mass and it will still balance!
Does that seem strange? It’s because although we associate gender with pronouns (he/she), mass is not gender-associated. Mass is an intrinsic property of an object that depends on its composition but not its identity.
The heavier child should sit closer to the end of the seesaw
When one child is significantly heavier than the other child, things get a little more tricky. In this case, the heavier child should still sit closer to the end of the seesaw, but they should also sit on both sides of the pole.
By sitting on both sides of the pole, they are forcing more weight onto their side of the seesaw, making it easier for them to stay up. The other child only has to worry about one side of the seesaw dropping because they are on both sides.
It is important to note that in this case, the heavier child should not be on their own side of the seesaw. They must share one with their lighter-weighted counterpart to ensure stability and safety.
The lighter child should sit closer to the end of the seesaw
A heavier child should sit closer to the end of the seesaw so that both children have an equal amount of weight to push up.
If the heavier child sits in the middle, then they will have to lift both ends of the seesaw, making it harder for them. The lighter child will not be able to keep up.
Theoretically, if one child was three times as heavy as the other, then they should sit on opposite ends of the seesaw- but only if they are perfectly matched in other physical qualities!
For instance, if one child was faster than the other, then having them sit on opposite ends would make it harder to keep balance. This is why ideally, children of similar size and speed should sit together on a balanced seesaw.
Find the center of mass for both children
First, you must find the weight of each child. We will call the child on the left side the left-child and the child on the right side the right-child.
To find the weight of the left-child, multiply their mass by the gravitational field strength (9.8 Newtons per kilogram). Then add this number to the total mass of both children. This is called total mass.
To find the weight of the right-child, multiply their mass by the gravitational field strength (9.8 Newtons per kilogram). Then add this number to the total mass of both children. This is called total mass.
The seesaw’s center of mass is where if you drew a line down through it, it would balance. To find this, first you have to find out how heavy each end of the seesaw is.
Keep the center of mass close to the ground
Balancing on a seesaw is all about weight distribution. If you can keep your weight close to the ground, you will have an easier time balancing.
That’s why when you stand up, you put most of your weight on your feet, not in the air. When you sit down, most of your weight is on the ground, not in the air.
If you stood on one foot in the air, most of your weight would be above the seesaw surface, making it harder to balance. If you sat down in a chair with your feet off the ground, you would have a hard time balancing.
In both cases, it would be harder to maintain balance because there is less contact between yourself and the ground. The same goes for jumping up and down in a soft spot like a beach- it’s harder to maintain balance because there is less contact between yourself and the ground.
Use a balance scale to determine which child is heavier
If you are determined to see who is heavier, then you need a different method. You need to find a way to put both children on the seesaw and have it balanced.
The only way to do this is to put one child on and then add weight until the seesaw is balanced. Then, you must remove some of that added weight and add your second child.
If the second child is lighter, then they must sit further out on the seesaw or else it will tip over. If they are heavier, then they must sit closer to the pivot point or else it will not balance.
Find the ratio of the two weights
The first thing you need to do is figure out how heavy the two people are on the seesaw. If you only know one person’s weight, you can still find the ratio of their weights on the seesaw.
If the boy weighs 100 pounds and the girl weighs 50 pounds, then he weighs twice as much as she does. So, put down that pencil—there’s no need to keep weighing them!
You can also do this with just one person on the seesaw. Suppose the boy weighs 100 pounds and there is no girl sitting with him. In that case, he must weigh twice as much as he does alone on the seesaw.
The key thing to remember here is that when there are two people on a seesaw, they each weigh half as much as they would alone.
Sit equal distances from the end of the seesaw
A seesaw is a playground apparatus that balances users depending on their weight. If you weigh twice as much as your partner, you should sit two times farther away from the end of the seesaw to keep it balanced.
If you both weigh the same amount, then you should sit equal distances from the end of the seesaw to keep it balanced. If one person weighs more than the other, they should sit three times farther away from the end of the seesaw to keep it balanced.
Does this sound confusing? It is easier to see it in action! Watch this video and see how easy it is to keep a seesaw balanced when people of different weights sit at different distances from the end.
