## Newton's first law, unless + past participle

4

I was reading Newton's first law:

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

In the part:

unless acted upon by an unbalanced force.

The meaning is clear but I had never seen this construction:

unless + verb (pp)


Is this construction correct?

Also if you can explain all the grammar of this last part (unless....) I would appreciate it so much

2

I asked the same question on English Language & Usage, if you don't want to click the link here is the answer:

In this context, the phrase

is a short-hand notation for

 You will see a similar type of shortened speech in an American legal context. They do it for the sake of brevity.