Force can be thought of as pressure. The force MUST act through some distance to be equivalent to energy - think of the air pressure you're sitting in right now (14 psi) - it's a force, but it isn't doing any work (acting through distance) so you can't equate it to energy. If that force pushed a rock a little ways, that would be a small amount of energy - if it pushed a rock a LONG way, that would be a lot of energy. It's one of those fundamentals of math and physics: energy has 2 dimensions (force AND distance) - if you only have one dimension, you don't have energy. Using your example, if you let a newton accelerate a mass for 1 second, that's one amount of energy - if you let a newton accelerate the same mass for 20 seconds, that's a lot more energy, but it's the same newton and the same mass!