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bouncy: bouncing or causing things to bounce.

https://www.lexico.com/definition/bouncy

I wonder why “a ball bouncy off the floor” is awkward but “a ball bouncing off the floor” is natural.

2 Answers 2

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"Bouncy" is, in this use at least, an adjective. It describes an attribute of a thing, such as a ball. "Bouncing" is a gerund or present participle (see note below). It describes the action of a thing, such as a ball.

The ball is bouncing off the floor

means that the ball is in the process of rebounding from the floor.

The ball is bouncy.

means that the ball is inclined to bounce, or tends to bounce.

The sentence:

The ball is bouncy off the floor.

has no obvious sensible meaning. I suppose it could mean that the ball is bouncy when off the floor, that it bounces fro walls but not from the floor. But that would be an awkward way of expressing such an idea, and he idea is unlikely, because no real ball does that. In any case this sentence certainly does not mean "The ball is bouncing off the floor" or anything similar to that.

Note that a "bouncy ball" is a term often used to describe a ball which retains a particularly large fraction of its momentum (up to 92% or more) when it bounces

Note on Terminology

The Wikipedia Article "Gerund" says:

Traditional grammar makes a distinction within -ing forms between present participles and gerunds, a distinction that is not observed in such modern grammars as A Comprehensive Grammar of the English Language and The Cambridge Grammar of the English Language.

The article goes on to say:

In traditional grammars, gerunds are distinguished from other uses of a verb's -ing form: the present participle (which is a non-finite verb form like the gerund, but is adjectival or adverbial in function), and the pure verbal noun or deverbal noun.

The distinction between gerund and present participles is not recognized in modern reference grammars, since many uses are ambiguous (citations omitted)

The article cites "Playing on computers is fun." as the use of a gerund, but "The boys playing on computers are my nephews.as the use of a present participle in traditional grammar.

By this standard te word "bouncing" in the sentence:

The ball is bouncing off the floor.

is probably a present participle, not strictly a gerund. But what ever term is used, it describes the action of the ball, what the ball is doing. In this it is unlike "bouncy" which describes the ball itself.

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  • "bouncing", in this context, is the present participle of "bounce", not a gerund. It's a reduced form of the phrase "a ball which is bouncing off the floor". Gerunds are nouns, and "a ball" + noun + "off the floor" makes no sense.
    – gotube
    Aug 10, 2021 at 4:01
  • @gotube A gerund is not a noun, although a gerund clause often functions as a noun. A gerund itself often functions as an adjective or adverb: in "a bouncing ball" "bouncing" modifies "ball" to describe what the ball is doing. I have modified the answer to address this in more detail. Aug 10, 2021 at 15:55
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I see that the definition you quote is unclear.

Note that "bouncy" is an adjective, not a verb. Thus, you can't say, "The ball is bouncy off the floor" because that would be using "bouncy" as a verb.

You can say, "This ball is bouncy", meaning, this ball tends to bounce a lot, or it is easy to make this ball bounce. Or you can say, "The bouncy ball is made of rubber." Either way, you're using "bouncy" as an adjective.

But you can't say "the ball is bouncying" because "bouncy" is not a verb.

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