You should aim for simplicity, concision and clarity. Be precise and choose your words carefully.
You can find more about the written style expected from lab reports under section 3 in the level 1 guidelines.
Compare the following sentences:
(a) The angular frequency of motion is (k/m)1/2, where k is the force constant of the spring and m is the mass of the body. The period of oscillation is therefore proportional to m1/2 .
(b) The angular frequency of motion is (k/m)1/2. Where k is the force constant of the spring and m is the mass of the body. The period of oscillation is therefore proportional to m1/2 .
(c) The angular frequency of motion is (k/m)1/2, where k is the force constant of the spring and m is the mass of the body, the period of oscillation is therefore proportional to m1/2 .
(d) The angular frequency of motion is: (k/m)1/2, where k is the force constant of the spring and m is the mass of the body. The period of oscillation is therefore proportional to: m1/2 .
The punctuation is correct in (a). In (b) a full stop is incorrectly used in lieu of a comma. In (c) a comma is incorrectly used in lieu of a full stop. In (d) the colons (:) are superfluous.
When should you use an apostrophe?
You use an apostrophe to indicate where you have omitted letters from a word, or even a complete word, for brevity.
Without using any apostrophes:
“Sheila has taken her own dogs and many of her friends dogs for numerous walks.”
With apostrophes:
“Sheila’s taken her own dogs and many of her friends’ dogs for numerous walks.”
In the explanation that follows we introduce the correct use of double and single inverted commas. An explanation of this comes later (vide infra, meaning “see below”.)
The first apostrophe indicates that the word “has” has been omitted. The second one needs more explanation. We use the apostrophe at the end of words when we are referring to a plurality. In this case Sheila has many friends whose dogs she walks. The word ‘omitted’ here is the word “their” so that we would have written: “….many of her friends, their dogs, for numerous walks.”
Alternatively, Sheila may only have one friend whose dog she walks. In this case we would have written: “….and her friend’s dogs for numerous…..”. The omitted word here is “her” so that we could have written: “…..and her friend, her dogs, for numerous…..”.
In the singular case, the word omitted may be; ”has” (as in; “Sheila’s taken”), “her” (as in; “Sheila’s dogs”), “his”, “is” (as in; “…it is…”), or “its” (as in; “...this Pizza’s cold…”)
So now you can see that when “Pizza’s” and “Kebab’s” are advertised for sale you might want to know just what it is that Pizza and Kebab have that is being sold (get it?)
This is quite simple. In the previous section, double inverted commas are used when we mean to indicate that something is literal. In other words exactly how we mean it to be presented. So when we used “Pizza’s” we really meant that this is how you would see it (with the incorrect use of the apostrophe) on a shop sign. When we use the single inverted commas as in ’omitted’, we meant that we did not mean that the word had been literally omitted.