# "A force is acting on a box until t = 10 seconds". Is the force still acting on the box at t = 10 seconds?

I have a difficulty to digest any sentence using the word until, especially when it is used to express something related to a point of time or space.

In the physics examination, I have a sentence as follows

A force is acting on a box until t = 10 seconds.

What can we infer from that statement whether or not the force is still acting at t = 10 seconds?

• In the actual physics examination this is irrelevant, because whether the force acts at the exact instant t=10 or not—i.e, whether the interval for which the force acts is the closed interval [0,10] or the half-open interval [0,10)—the answer will be the same for any reasonable physics question. Oct 19, 2010 at 3:15
• OK. Yes, the impulse can be still calculated. Let's ignore the physics. At t = 10 seconds, is the force still acting on the box? Oct 19, 2010 at 3:25

As ShreevatsaR says, the question is meaningless in the context of physics. So here are other examples with until where the time boundary can be interpreted:

To my ear, I was at the office until 5 PM includes the boundary -- it implies I was at the office at 5 PM. I won't see you until I get home, on the other hand, seems to me to allow situations in which I'll see you as I get home, thus excluding the boundary. Reasonable people may disagree.

Depending on the context, until now can include or exclude now:

Expanding the company will change what until now has been a friendly culture.
Until now, scientists didn't know why gravity matters.

Until today and until tomorrow both change their situation at some point during the boundary condition/day.

Summary: until has no specific effect on the boundary. The boundary determination, in the rare cases where it has a meaning, is a semantic and contextual issue of the sentence, rather than of until.

I think with "until" there is some implication that there is a change in the situation at t = 10. This may or not be a change in whether the force is still acting. I think additional info to remove ambiguity will be needed in the next phrase sentence.

• Assume the change in force is the only possibility. Oct 19, 2010 at 4:10
• I agree that without further qualification, the question can't be resolved. At least, as a question about until. Perhaps it can as a physics problem. :-) Oct 19, 2010 at 5:15
• @Mike: Not as a physics problem, since (as ShreevatsaR says in his comment to the main question) the force at a given instant is irrelevant to a physics problem (as opposed to force over even a very short interval, which can be relevant). It's a language question. Oct 25, 2010 at 21:26

I agree with Ophiuroid that the conditions at the moment of the until depend on the context. Here are two examples using the sentence in question.

In the first example, the condition changes prior to the specified moment.

All of the boxes should be undisturbed throughout the entire process. But—as you can see from the sensor data—this is not the case for most runs. A force is acting on a box until t = 10 seconds. At that point, the data show the anomalous force has disappeared.

In the second example, the condition changes after the specified moment.

Once you disable the alarm you enter the gallery, but then wait before touching any of the boxes. A force is acting on a box until t = 10 seconds. After that, it is safe to grab the box that was moving and exit the gallery.