Tone refers to the writer's voice in a written work. It is what the reader or hearer might perceive as the writer's attitude, bias, or personality. Many academic writers mistake a scholarly tone for dull, boring language or a mixture of jargon and multisyllabic, "intelligent-sounding" words. Academic writing, however, does not need to be complicated nor lacking in style (see APA 7, Section 4.7); instead, it can be both engaging and clear.
You should speak as an objective social scientist. This means that everything you say must be unbiased, scholarly, and supported by evidence. According to APA (2020), differences in research "should be presented in a professional, noncombative manner" (p. 114).
Avoid slang, text-message or SMS spellings, clichés, and contractions. Phrases like "digging sports," "wicked cool," "maxed out," "clear the air," "heading south," "the cat's out of the bag," "thru the roof," "hear their spin on it," "so to speak," and "in the hands of" have no place in academic writing. These casual expressions may be appropriate in personal emails, but they are inappropriate in research papers. Use standard US English spelling for all words, and if you are not sure if a word is a slang term, look it up in the dictionary.
Take a look at this example. The first paragraph is written in an informal way. The second is revised to keep a formal tone:
When I got my students to think science was wicked cool, their test scores went through the roof! When I asked for their spin on their improvement, they just said the test felt like a piece of cake to them after I had implemented the new curriculum changes.
Revised to be more formal:
When I was able to engage my students and get them interested in science, their test scores improved significantly. I asked a few students why they thought the scores had improved, and they admitted that the test seemed much easier because of the new curriculum.
Note that this video was created while APA 6 was the style guide edition in use. There may be some examples of writing that have not been updated to APA 7 guidelines.