I own two beautiful red merle collie cross sisters, they are two years old,  before leaving my 9-5 job, could only give them one hour of free running a day.
They were quite naughty, often eating my furniture, and seeming rather bored and unhappy.

Now though i have quit my job and now can take the dogs on a good 3 hours a day.
I dont know whats happened, but these dogs are totally different, they are very happy and i have no trouble with them!

does more exercise make a dog happier?

Kate, Mia and Tia.

um yes

Yes, because you are tiring them out so they rest, also you are there with them so I assume they are getting more attention!

Rox

Its not just a matter of physical exercise....  many dogs can be destructive if not MENTALLY stimulated. It is important not to physically over exert a young dog to tire it out, but to offer it brain exercise too, like any form of obedience training, agility work etc.

I think they just like your company, no dog is totally happy if part of what they consider their pack is missing. Dogs do not understand the necessities of earning a living.