兩者均可表示“快”，在口語中，一般多用quick(尤其在需要用比較級或最高級時)，并且總是放在動詞之后；若放在動詞之前，一般用quickly。如：

Come quick(ly). There's been an accident. 快來，出事故了。

You get there quicker by bus.
你坐汽車去那兒會快一些。

He quickly changed his clothes.
他迅速地換了衣服。

The evening passed quickly. 晚上很快過去了。

He ran as quickly as he could. 他使勁地跑。

It gets hot quickly when the sun comes. 太陽出來了天很快熱起來。

I was wondering how to get there quickly. 我想知道怎么能很快地到達那里。

He quickly availed himself of the opportunity. 他很快利用了這個機會。

After his wife's death he aged quickly. 他妻子死后他老得很快。

Relief was quickly sent to sufferers from the great fire.
救濟物資迅速送到大火中受害人的手中。

How quickly time passed! It might have happened yesterday.
時間過得真快! 這仿佛是昨天發生的事似的。