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You found a video that finally makes a chapter click. Before you copy its method into your notebook, spend two minutes checking it.
Can you trust a science video because it is popular?
No. Joachim Allgaier searched YouTube with ten search terms on climate change and climate engineering and analysed the first 20 videos for each, 200 in all. Of these, 107 opposed the scientific consensus, and the videos supporting the consensus drew only slightly more views than those opposing it (Frontiers in Communication, 2019). Climate is not physics homework, but the lesson carries over: a search ranking measures attention, not accuracy.
Good explainers also do something that feels less smooth. In a 2008 study by Derek Muller, Manjula Sharma and Peter Reimann, students learned Newton's first and second laws from a short multimedia lesson; 272 students took part across the experiments. In the first experiment, those who watched a video dialogue that raised common wrong ideas reported investing more mental effort and scored higher on the post-test than those who watched a standard lecture-style presentation (Science Education). A video that names the trap and shows why it fails is doing the more useful job.
How do you know if a YouTube science explanation is correct?
Run these six checks.
Does it match your NCERT chapter? Open the chapter on the same topic and compare the definitions, symbols and sign conventions. If they differ, the video may be using another book's convention, and you need to know which one your exam follows.
Does it state its assumptions? Listen for "ignoring air resistance", "for an ideal gas", "for small angles" or "x is positive". A formula without its conditions is half a formula.
Does it show units at every step? Units should be written beside numbers and should balance on both sides of every equation. The SI, which has seven base units such as the metre, kilogram and second, is the internationally agreed system for measurement (BIPM).
Does it handle a counterexample? Ask: is there a case where this rule fails? A good explanation tells you where its rule stops working.
Does it cite sources? Look in the description and on screen for the textbook, paper or official page behind each claim, especially for numbers and history.
Who made it? Leave the video and search for the channel or presenter in a new tab. In a study of 45 experienced internet users, professional fact checkers read laterally like this, opening new tabs to judge a source, and reached more warranted conclusions in a fraction of the time taken by historians and Stanford students, who tended to stay on the original site (Wineburg and McGrew, Teachers College Record, 2019).
Worked example 1: does a heavier ball fall faster?
Say a video claims: "All objects fall at the same rate, so the time to fall from height h is t = √(2h/g)." Take h = 20 m and g = 9.8 m/s². Then t = √(40 ÷ 9.8) ≈ 2.0 s.
Units: √(m ÷ m/s²) = √(s²) = s. The answer comes out in seconds, as it should. See our 30-second dimensional analysis check.
Assumption: the formula holds only if air resistance is negligible. A good video says so out loud.
Counterexample: drop a feather and a coin in your room. The feather loses, which exposes the assumption rather than breaking the rule. On the airless Moon, Apollo 15 commander David Scott dropped a 1.32 kg hammer and a falcon feather together, and they hit the ground at the same moment (NASA).
Verdict: correct, if the video states the assumption. If it says "always", it has failed check 2.
Worked example 2: is √(x²) always equal to x?
A maths shortcut video simplifies √(x²) to x. Test a counterexample: put x = −3. Then √((−3)²) = √9 = 3, not −3. The correct statement is √(x²) = |x|, and it equals x only when x ≥ 0.
One number broke the rule, so the video failed checks 2 and 4 together. To catch this yourself, try a negative number, zero or a very large value.
What should you do when a video fails a check?
Do not throw the whole video away. Note the timestamp, write what you think is wrong, and check it against your textbook. Then say it in your own words: "The video says ___. It assumes ___. It breaks when ___." If you cannot fill the blanks, that is the part to study.
Our guide on how to learn from video lectures shows how to pause, predict and test yourself as you watch, and the same habit of checking applies to AI answers, as in how to check references and citations.
If the gap is a concept rather than one step, the Fermi Concept Library has every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson. And Fermi's AI tutor notices where you are stuck and decides whether to explain, ask or show, so you can test the video's claim with a question of your own.
