The verb 'to pat' means to strike gently with the palm of the hand or with something similarly flat.
pat指用手掌或同样平展的什么东西打击、抚摸
'To tap' means to strike with an implement, for example a pencil or a hammer, but it could be a finger or the beak of a bird. These latter two items could be considered to be implements for the purpose of this explanation.
tap指用工具打击、抚摸，比如，一支铅笔或一个锤子，但也可以是一根手指或者是鸟喙。后面的这两项在这一解释中可以被当做工具。
Note that 'to tap' also has other meanings, for example drawing something (typically a liquid) out of a container.
注意：tap也有其他的意思，比如用一种容器泼画什么东西（通常用液体）
pat on something" may impart the sense you would strike gently a small area of an object etc. whereas "pat something" may not
（此外），pat on something可以传达出一种轻击某一物体的小块区域的意思，而pat something 不可以