The state of having no weight — the noun for the condition weightless describes.

The state of having no weight指完全沒有重量的狀態—— the noun for the condition weightless describes是形容詞weightless所描述的那個狀態的名詞形式。

It is mostly a science and space word: astronauts train for weightlessness in a big water tank, and long periods of weightlessness make muscles and bones grow weaker. Because it is a noun you use it for the condition itself, not for a person or thing: "the effects of weightlessness on the human body".

It is mostly a science and space word它主要是科學和太空用語： astronauts train for weightlessness in a big water tank太空人會在大水槽裡訓練適應失重， and long periods of weightlessness make muscles and bones grow weaker長時間處於失重狀態會讓肌肉和骨骼變弱。 Because it is a noun you use it for the condition itself, not for a person or thing因為它是名詞，用來指狀態本身，而不是指人或物： "the effects of weightlessness on the human body"「the effects of weightlessness on the human body（失重對人體的影響）」。

Outside science it can describe a feeling — the weightlessness you feel when a lift drops quickly, or the pleasant weightlessness of floating in the sea. It is a long, formal-sounding word; in speech people more often just say "zero gravity" or "being weightless".

Outside science it can describe a feeling在科學之外，它也可以形容一種感覺—— the weightlessness you feel when a lift drops quickly電梯快速下降時你感覺到的那種失重感、 or the pleasant weightlessness of floating in the sea或是漂浮在海裡那種舒服的失重感。 It is a long, formal-sounding word這是個又長又正式的字； in speech people more often just say "zero gravity" or "being weightless"講話時人們更常直接說「zero gravity（零重力）」或「being weightless（處於失重）」。