The way I understand it: Passive voice = "to be" + past participle (see: http://www.unc.edu/depts/wcweb/handouts/passivevoice.html before you shoot me down if I'm wrong ) One of the things I'm struggling with is rewriting a sentence which I believe is in the passive. I know not all sentences in the passive are wrong and maybe this is one such case, but I'd like you to take a look. The sentence is: I can't figure out how to turn that into active. Maybe it's just a bad sentence, or maybe it's a perfectly good one or maybe I'm overthinking this. Take a look.
How about showing an action to indicate his weariness? Like maybe he slumps down in a chair, or against a tree. Something like this would be better shown than told imo. I don't know what led up to this scene, or where Bob is and why he is exhausted, but maybe this would be of help...as an example that is. The adrenaline charged minutes of the chase caught up with Bob as he slid to the ground, his chest heaving. It makes for a longer sentence but it is one that I would rather see. Not to say that using the passive voice is bad. In the example you used I have no problem with it other than it is telling rather than showing.
It's not simply a matter of the verb "to be", although that is one of the weakest verbs you can use. Sometimes it's the only verb that fits, but it leaves you dependent on adjectives and adverbs. Passive voice is characterised by actions upon a character, rather than by a character. In the strictest sense, passive voice uses the verb "to be" with an inanimate subject, and the person appearing as a direct or indirect object, or obhect of a preposition. You are most likely to find it in very stiffly written research articles: Your example has adrenaline as the subject, and Bob is practcally an afterthought. You could strengthen it by making him the subject: This still has "to be" as the verb, so it could still be inproved, but you would have to modify the meabning in the process: You cannot always make improvements out of context. If you have a clearer idea of what Bob is doing at the time, you can choose better verbs to descrivbe the actual effect of his running off the adrenaline boost. In describing action, the usual quality hierarchy is that a good verb choice is more effective than a good adjective choice, and a good adjective is better than a good adverb. Adjectives are usually more precise than adverbs, but nothing conveys action better than just the right verb. On the other hand, a passive voice can be very effective in dropping the pace, so it might be very effective to reinforce that your chaacter is running out of steam. Therefore, the deliberate choice of passive voice is a tool you can use.
Passive voice is actually an issue of subject/object inversion. it is accompanied by version of "to be" in English, because that is really the only way it can be shown. I think the correct phrasing of your original sentence would be: "The adrenaline had long since been siphoned from Bob's body, leaving him feeling weary." Cog offers two adequate alternatives.
I think Garmer has hit the crux of the matter. Passive or active, the sentence in question is tell, not show. As Garmer has mentioned, give the reader a picture of exhaustion, not just the dry fact of said exhaustion. The fact that the sentence is in the passive voice is really a secondary issue, as pointed out by Cogito, because the correct and deliberate use of passive voice has its place and use. A bit melodramatic, I admit, but I’m using literary conceit to make the point.
Garmar created a thread in Gen. Writing which quoted me, but that was more discussing Show vs Tell as opposed to my question about the passive being made active.
etan is correct in correcting that incorrectly worded sentence... ;-) to make it active, all you need do is change 'had long since been siphoned from' to 'had long since left'... when you lose the auxiliary verb, you go from passive to active...
I think something like the following would paint a decent picture. Out of breath, Bob leaned against a tree. He dragged in hard deep breaths. After the adrenaline rush faded, he sat down on a bench and slumped down into it relaxing all his muscles.
a bit overmuch on detail, imo, for a compelling read... and scrambled syntax in that first sentence... 'less is more' is still the best axiom for writers to follow...