This is the 6899th most frequent Chinese word.
激
"激" means "to stimulate, arouse, excite, or intensify."
Here, '激动' means 'excited', and '激' is used to describe a strong emotional reaction.
这个音乐让我感到非常激动。
This music makes me feel very excited.
In this case, '激起' means 'to stir up', and '激' conveys the action of causing turbulence or movement.
雨水激起了池塘中的涟漪。
The raindrops stirred ripples in the pond.
Here, '激烈' means 'intense', and '激' indicates severity or intensity in the context.