Equivalence principle

From this principle, Einstein deduced that free-fall is actually inertial motion. Objects in free-fall really do not accelerate, but rather the closer they get to an object such as the Earth, the more the time scale becomes stretched due to spacetime distortion around the planetary object (this is gravity). An object in free-fall is in actuality inertial, but as it approaches the planetary object the time scale stretches at an accelerated rate, giving the appearance that it is accelerating towards the planetary object when, in fact, the falling body really isn’t accelerating at all. This is why an accelerometer in free-fall doesn’t register any acceleration; there isn’t any. By contrast, in Newtonian mechanics, gravity is assumed to be a force.

— Wikipedia on Equivalence principle

2012.03.23 Friday ACHK

唔識就飛 9

這段改編自 2010 年 5 月 26 日的對話。


* This item was deleted.

Note. Figures in brackets indicate the percentages of candidates choosing the correct answers.

General note on item deletion

It is normal for the HKEAA to delete a small number of items from its multiple-choice question papers if they prove unsatisfactory. In practice, there are a number of reasons why this is considered necessary. By far the most common reason for deleting an item is that the item fails to discriminate between weak and able candidates — in other words, the majority of the candidates involved had to rely on guesswork in answering that question. If such an item is retained, the measurement process is rendered less effective. Where items have been deleted in the live papers, they are still included in this series of publications. They are indicated as deleted items. Such items may be discussed in the corresponding examination reports.



在香港的中學公開試中,間中有一些多項選擇題(multiple choices),會在考試後被考試局刪除。換句話說,那些題目的分數,不會計算在總分之中。

某一題被刪除,其中一個可能的原因是,該題每個答案的選擇人數差不多,都是大概 25%。那就即是話,大部分人也是隨意估計的。那樣,該題就失去了考試的意義,因為它不能再用來,判別考生學問的高低。




— Me@2012.03.23



2012.03.23 Friday (c) All rights reserved by ACHK