上 is pronounced as soeng5 when it indicates a movement or action, usually as a verb or adverb. e.g. 上山(soeng5 saan1)(go up a hill), 上車(soeng5 ce1)(get in a car), 上堂 (soeng5 tong4)(attend a class), 爬上樹(paa4 soeng5 syu6)(climb up a tree), etc. 上 is pronounced as soeng6 when it refers to a position or time, usually as an adjective or a preposition. e.g. 檯上(toi4 soeng6)(on the table), 籃球場上(laam4 kau4 coeng4 soeng6)(in the basket ball court), 上星期(soeng6 sing1 kei4)(last week), 上午10點(soeng6 ng5 sap6 dim2)(10 am), etc. 下 is pronounced as haa5 only when it means "once", "for a short while", "briefly", etc. e.g. 睇下(tai2 haa5)(have a look), 打一下(daa2 jat1 haa5)(hit once), 試下啦!(si3 haa5 laa1)(Just try!), etc. Some people would write 吓 instead of 下 for this usage. In all other cases, 下 is pronounced as haa6. These are just general guidelines for your reference. They do not cover all usages and there may also be exceptions.

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