网上看到如下题目。天平左边，一个乒乓球悬浮于一杯水内；右边，一个铁球悬挂浸入一杯水内。两边的水杯一模一样，水的刻度相同。乒乓球和铁球大小一样。
乱花渐欲迷人眼，先不过多考虑拉力、浮力啥的。俺的思考，做了个小的思想实验：
1.左边的水假设是不透明的，则你看到的就是一杯水，只不过水缺了一个乒乓球大小的体积。当然还要加上乒乓球和里面的空气，这个可忽略不计。
2.假设右边铁球的密度慢慢变小，最终变成了水的密度，则悬挂铁球的绳子拉力变成0。右边就是一整杯水，并没有缺少球体体积的水。
所以右边重。
Which Side is Heavier? A Simple Physics Problem and a Thought Experiment
Just came across the following problem online. On the left side of a balance, a ping pong ball is suspended in a glass of water; on the right side, an iron ball is hanging and submerged in a glass of water. Both glasses are identical, and the water levels are the same. The ping pong ball and the iron ball are the same size.
Amidst the confusing details, let’s set aside considerations of tension and buoyancy for now. Here’s my thought process through a simple thought experiment:
- If we assume the water on the left side is opaque, what you see is just a glass of water, missing a volume equivalent to a ping pong ball. Of course, we also need to account for the ping pong ball and the air inside it, which is negligible.
- If we gradually reduce the density of the iron ball on the right side until it matches the density of water, the tension in the string holding the iron ball would become zero. Thus, the right side would be just a full glass of water without any missing volume due to the ball.
Therefore, the right side is heavier.