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A Clock That Could Ride the Waves

6th grade nonfiction passage about finding longitude at sea: 230 words, six questions, an answer key and vocabulary.

6th grade nonfiction finding longitude at sea 230 words

A Clock That Could Ride the Waves

Long ago, sailors on the open ocean faced a puzzling problem. By measuring the sun or the stars, they could tell how far north or south they were. But they could not tell how far east or west they had sailed. That east-west distance is called longitude, and without it a ship could easily lose its way or miss a small island.

The answer lay in time. The Earth turns once every day, so noon arrives at different moments in different places. If a crew knew the exact time back at its home port, and also the local time where the ship was, they could compare the two and work out their longitude. The hard part was keeping the home time accurate. Pendulum clocks, the best clocks of the day, did not work well on a ship that rolled and pitched on the waves.

In the 1700s, an English clockmaker named John Harrison set out to build a clock that could. He worked for many years and made several versions, each better than the one before. His smaller timekeepers used tiny springs and moving parts in place of a swinging pendulum, so the rocking of the ship did not upset them. On test voyages, they kept very good time.

Thanks to clocks like these, called marine chronometers, sailors could at last find their place on the sea with confidence.

Questions

  1. What could sailors learn by measuring the sun or the stars? in the text

  2. What is longitude? in the text

  3. Which two times did a crew compare to find longitude? in the text

  4. Why did pendulum clocks fail at sea? in the text

  5. What did Harrison use in place of a swinging pendulum? in the text

  6. Why could a crew with an inaccurate clock not find its longitude? think about it

Words to know

longitude
how far east or west a place is on the Earth
accurate
correct and without mistakes
pendulum
a weight that swings back and forth to keep a clock's time
voyages
long trips over the sea
chronometers
very exact clocks used to find a place at sea
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 187 words · Flesch-Kincaid grade 2.4

Long ago, sailors had a hard problem. They could use the sun or stars to tell how far north or south they were. But they could not tell how far east or west they had sailed. That distance is called longitude. Without it, a ship could get lost.

The answer was time. The Earth turns once a day, so noon comes at different times in different places. A crew could use the time at their home port and the time where the ship was. They could compare the two to find their longitude. But the home time had to be exact. Pendulum clocks did not work well on a ship. The ship rolled on the waves.

In the 1700s, an English clockmaker named John Harrison tried to build a better clock. He worked for many years. He made several clocks, and each one was better. His small clocks used tiny springs instead of a pendulum. The rocking of a ship did not bother them. On test trips, they kept very good time.

Clocks like these are called marine chronometers. They helped sailors find their place at sea.

▲ This passage · 230 words · Flesch-Kincaid grade 6

Long ago, sailors on the open ocean faced a puzzling problem. By measuring the sun or the stars, they could tell how far north or south they were. But they could not tell how far east or west they had sailed. That east-west distance is called longitude, and without it a ship could easily lose its way or miss a small island.

The answer lay in time. The Earth turns once every day, so noon arrives at different moments in different places. If a crew knew the exact time back at its home port, and also the local time where the ship was, they could compare the two and work out their longitude. The hard part was keeping the home time accurate. Pendulum clocks, the best clocks of the day, did not work well on a ship that rolled and pitched on the waves.

In the 1700s, an English clockmaker named John Harrison set out to build a clock that could. He worked for many years and made several versions, each better than the one before. His smaller timekeepers used tiny springs and moving parts in place of a swinging pendulum, so the rocking of the ship did not upset them. On test voyages, they kept very good time.

Thanks to clocks like these, called marine chronometers, sailors could at last find their place on the sea with confidence.

■ Harder · 249 words · Flesch-Kincaid grade 9.1

In earlier centuries, sailors crossing the open ocean confronted a baffling difficulty. By measuring the position of the sun or the stars, they could determine how far north or south they had traveled. Yet they had no means of telling how far east or west they had sailed. That east-west distance is called longitude, and without knowing it, a ship could easily lose its course or sail past a tiny island without ever seeing it.

The solution depended on time. Because the Earth rotates once every day, noon arrives at different moments in different places. If a crew knew the exact time back at its home port, and also the local time at the ship's position, they could compare the two and calculate their longitude. The challenge was keeping the home time accurate. Pendulum clocks, the finest timepieces of the age, performed poorly aboard a vessel that rolled and pitched on the waves.

During the 1700s, an English clockmaker named John Harrison resolved to build a clock that could handle such conditions. He labored for many years and produced several versions, each an improvement on the one before. His smaller timekeepers relied on tiny springs and carefully balanced moving parts in place of a swinging pendulum, so the rocking of the ship did not disturb them. On test voyages, they kept remarkably good time.

Thanks to instruments like these, known as marine chronometers, sailors were at last able to determine their position on the sea with real confidence.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put longitude, accurate, pendulum, voyages and chronometers on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 6 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "A Clock That Could Ride the Waves"?

It was written for 6th grade. It has 230 words and works out to a Flesch-Kincaid grade level of about 6.0. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 5 ask for something the text says directly and 1 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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