What are the differences between an upright piano and a grand piano?

The main differences between an upright piano and a grand piano are:
- action mechanisms: an upright piano utilizes a string action to allow vertically placed hammers to reset, while gravity returns the hammers in a grand piano, offering better responsiveness and repetition speed
- pedals: a grand piano usually have 3 pedals, and an upright piano has 2 or 3 pedals with different functions.

Though it depends on the specific models and conditions, a grand piano usually offers better dynamic range and richer resonance than an upright piano.