The tears released as an emotional reaction are caused by hormones, as a natural response. They are intrinsically different from tears that we shed when peeling onions. The chemical composition of the tears is different.
Onions cause a chemical reaction that makes the eyes burn. The water that comes out is a reaction to the vapours from the onions that get into the eyes. There are many other elements that make our eyes water. Dust particles in the eyes can cause that to happen, as does heavy smoke. Tear gas, also makes our eyes water. An allergic reaction can make the eyes to water.
Please recognise the difference between tears and watering of eyes.
"A love affair with knowledge will never end in heartbreak." -Michael Garrett Marino
Again crying is not the indication of low strength. It is an emotion. These tears are caused by hormones and basically, this is out of emotions only. But some people, when they are weak, will go on weeping for a long time and that is a disease known as hysteria. This is also out of emotions and they are not able to control their emotions due to their weakness. Those people who are suffering from this disease have to consult a physician.