Study sets
Why does the Moon change shape?
The changing view
Study guide
Keep notes, key concepts and practice questions from the same lecture together.
Explore study setsAI YouTube Video Summarizer Turn a lecture into a study set.
Paste a YouTube lecture link to get chapter notes in English. Follow a timestamp back to a worked example, then check what you remember with a quiz or flashcards.
Create a free accountSummarize a YouTube lecture in three steps
Step 1. Paste your YouTube link
Choose a video with captions. Paste its link into YouTube Summarizer and choose the language for your notes.
Step 2. Read the chapter notes
Scan the key points, then select a timestamp to see the explanation in context. This is especially handy when a lecturer writes a formula on the board.
Step 3. Make a study set
Save the lecture notes, practice terminology with flashcards and apply the ideas in a quiz. Revisit the relevant chapter if you get stuck.
From a one-minute clip to an exam question
Why isn't there a lunar eclipse every full moon? Go to 0:32 in the astronomy lesson and test your explanation. You can also try a retail math problem or a history source exercise.
Why does the Moon change shape?
Sunlight illuminates half of the Moon. How much of that half we see changes as the Moon orbits Earth.
A full moon shows us almost the whole daylit side. A lunar eclipse happens only when the Moon passes through Earth's shadow.
Where moonlight comes from
0:00Moonlight is sunlight reflected from the surface.
Look at the crescent. Sunlight reaches the lunar surface and bounces toward Earth. About half of the Moon is lit at any moment.
The changing view
0:15The visible fraction of the daylit side changes.
As the Moon moves, we see it from a different angle. At first quarter, half of the visible disk looks bright even though half of the entire globe is still lit.
Full moon or eclipse?
0:32The Moon's orbit is tilted.
At full moon the Moon usually passes above or below Earth's shadow. It darkens during an eclipse only when it actually crosses that shadow.
Model a moon phase
Shine a lamp on a ball.
Move around the ball and notice which part looks bright.
Explain why the lamp still lights half the ball.
A crescent grows into a half moon. What has changed?
Exactly. The Moon moved and the viewing angle changed.
Where does moonlight come from?
The Sun. The lunar surface reflects its light.
What changes between a crescent and first quarter?
Our viewing angle and the fraction of the lit side we see.
Why isn't every full moon an eclipse?
The tilted orbit usually carries the Moon clear of Earth's shadow.
Two discounts on one jacket
Two successive 20% discounts bring a $50 jacket down to $32.
Each discount leaves 80% of the previous price. Multiplying 0.8 by 0.8 leaves 64% of the original, a 36% reduction.
The first sale price
0:0020% of $50 is $10.
A jacket costs fifty dollars. A twenty-percent discount takes off ten dollars. Its new price is forty dollars.
A new starting price
0:16The second discount is 20% of $40.
At checkout you receive another twenty percent off. Apply it to forty dollars. Eight dollars come off, leaving thirty-two dollars to pay.
Multiply the two factors
0:33Two factors of 0.8 give 0.64.
Each time, you pay eighty percent of the previous price. Multiply the two factors to find the overall change.
Try another price tag
Start with an $80 jacket.
Take 20% off twice, using the new price each time.
Check that $80 × 0.8 × 0.8 equals $51.20.
A $20 shirt is discounted by 10% twice. What's the final price?
Correct. The second discount takes $1.80 off $18.
How much do you save the first time?
Ten dollars.
Which price is the second discount based on?
The reduced price of $40.
What multiplier represents 20% off?
0.8, the fraction you still pay.
What can a strike letter tell us?
An eyewitness letter describes one factory gate. It cannot establish a citywide headcount.
In this fictional exercise a later account cites the same letter. Check where each piece of evidence comes from before counting it twice.
At the factory gate
0:00The writer saw a group at one gate.
Imagine a worker writing that evening: I saw around twenty people at our gate. The location and time limit what this observation can establish.
Tracing a later account
0:17A later text cites the original letter.
Thirty years later, a commemorative booklet repeats the number. Its footnote leads back to the letter.
Estimating the citywide strike
0:36A citywide claim needs evidence from other workplaces.
Look for strike lists and independent accounts from other gates. Ask who was missing before adding up the figures.
Observation or inference?
Underline what the writer personally saw.
Draw an arrow from the letter to the later account.
Write one question that requires another source.
A newspaper repeats the booklet's figure. How many independent observations are there?
Exactly. All three texts rely on the same observation.
What did the worker actually observe?
Roughly twenty people at one gate.
Are there now two independent observations?
No. Both texts rely on the same witness.
What else could show the scale of the strike?
Independent records covering other workplaces.
Lunar imagery from NASA Scientific Visualization StudioFind the part of the lecture you need.
Timestamped chapters
Go straight to the worked example instead of scrubbing through the whole lecture.
Brief or detailed notes
Preview a topic before class or read the intermediate steps when revising a difficult argument.
Transcript alongside your notes
Compare a summary point with the lecturer's wording. Open the corresponding moment to see a diagram or demonstration.
Questions tied to the video
Ask why the second discount uses a different price. Follow the reference to check the calculation.
Notes in your study language
Take notes in English from a Spanish lecture while keeping the original terminology in the transcript.
Portable lecture notes
Download a text file with chapter headings, key points and timestamps for your own course notes.
Three ways to study with video
BEFORE CLASS
Preview an unfamiliar topic
Read the overview and write down a question you'd like the lecture to answer.
DURING REVISION
Find the missing step
Two successive 20% discounts add up to 36%. Revisit the price used for the second discount.
BEFORE THE EXAM
Practice explaining it
Answer with your notes closed, then check the source if your explanation leaves a gap.
Keep studying with your lecture notes
Quizzes
A $20 shirt is discounted by 10% twice. What's the final price?
$16.20
Apply a lecture idea to a new problem and check the feedback.
Explore quizzesFlashcards
What did the worker actually observe?
Roughly twenty people at one gate.
History
Recall a term or definition before turning the card over.
Explore flashcardsYouTube summarizer FAQ
How do I summarize a YouTube video?
Paste the link to a captioned video, choose your notes language and create the summary. Each chapter includes key points with timestamps.
What kinds of videos work?
Use a captioned lecture, interview or walkthrough with spoken explanations. Check the original frame for information shown only on screen.
What if a video has no captions?
The tool needs captions to build its summary. Look for Show transcript in the YouTube description or choose a captioned recording.
Can I get English notes from a lecture in another language?
Yes. Choose English for the summary and use the transcript to check a term in the lecturer's language.
Can I ask about one specific calculation?
Ask your question about the video and open the timestamp in the answer to check the lecturer's reasoning.
How do I make flashcards and quizzes?
Create a study set from the lecture. Pick flashcards for quick recall or a quiz to practice a longer explanation.
Can I download the notes?
Yes. The text download includes chapter titles, key points and timestamps.
Do I need an account to save a lecture?
A free student account lets you save a lecture in a study set and return to it later.
Plans and pricing