重さ

1. Origins, structure, and basic meaning

• Structure: 重さ(おもさ) is the noun form of the quality expressed by 重い(おもい) and refers to weight.
• Basic usage: It is used for the weight felt when lifting a box or a weight limit applied to vehicles.

2. Common pitfalls and similar expressions

• Being heavy and having a weight
  • 重い箱 means a heavy box.
  • 箱の重さ names the box's weight as a measurable property; it does not itself judge the box to be heavy.