Classical guitar came to us from Spain and, in its present form, exists since the XVIII century. Acoustic guitar appeared much later, in the early twentieth century. Then there was a need to increase the volume for a speech from the stage. For this purpose the body of the guitar was enlarged and became more common steel strings.
If you put Radom classical and acoustic guitar, once you can see the difference in size. The body of an acoustic guitar much more, making it louder and louder. Such guitars often set the metal strings. Classical guitar has a smaller body size. Classic set nylon strings, which sound softer and deeper steel.
Besides the differences you can find in the structure of the fretboard. On classical guitar it is made of solid wood. The inside of the neck of an acoustic guitar set steel anchor, which compensates for string tension and temperature change. The anchor also serves to adjust the distance between the strings and fretboard. Even visually you can see that the fingerboard of a classical guitar is wider and thicker. Acoustics it is more like a fretboard electric guitar. In addition, there are differences in the structure of the peg line mechanism.
In connection with constructive distinction, differ and scope of guitars. Classical guitar play classical music and also Spanish music. It is on the classics are taught to play musical schools and colleges. Acoustic guitar play mostly rock, street songs, pop music, etc.
So, it is clear that the differences between the classical and acoustic guitar quite a lot. Therefore, the choice of guitar depends on what kind of music it is supposed to do.