There are several synonyms for the phrasal verb "knock over" which means to cause something to fall or to knock it down. One synonym is "topple" which implies something falling suddenly or violently. Another word is "upend" which means to turn something over completely. "Overturn" is another synonym which suggests a sudden or accidental change in position. "Capsized" is also a good option when referring to boats or ships. "Bump into" is a less forceful synonym for accidentally knocking something over. "Collide with" suggests greater force and could refer to a vehicle crashing into an object or another vehicle.