Why the tides rise and fall

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Table, Tide table for a beach (model data), with columns Tide, Time, Height (m)

   High, 5:10 a.m., 1.8; low, 11:22 a.m., 0.3; high, 5:35 p.m., 1.7; low, 11:47 p.m., 0.4.

2. 1.

   Bo reads the tide table before exploring tide pools. What is the drop from the morning high to the late-morning low?

   • 2.1 m
   • 1.8 m
   • 0.3 m
   • 1.5 m
3. 2.

   Using the tide table, about when will tomorrow's first high tide come, by Esme's math?

   • About 4:20 a.m.
   • About 6:00 a.m.
   • About 5:10 a.m., the same as today
   • About 5:35 a.m.
4. 3.

   How long is it from the 5:10 a.m. high tide to the 5:35 p.m. high tide, by Jun's math?

   • 24 hours 50 minutes
   • 12 hours 25 minutes
   • 6 hours 12 minutes
   • 12 hours
5. 4.

   Tidal force ∝ mass ÷ distance³; Sun 27 million times the mass, 390 times the distance. NOAA: the Sun has 27 million times the Moon's mass but is 390 times as far away. Tidal force ∝ mass ÷ distance³. Compare the Sun's tidal force with the Moon's, by Kira's math.

   • About 177 times stronger
   • About 0.46, under half
   • About 27 million times stronger
   • About 69,000 times stronger
6. 5.

   Gravity ∝ mass ÷ distance²; Sun 27 million times the mass, 390 times the distance. Gravity ∝ mass ÷ distance². With the same numbers (27 million times the mass, 390 times as far), how does the Sun's pull on Earth compare with the Moon's, by Luz's math?

   • About 27 million times stronger
   • About 177 times stronger
   • About 0.46 times as strong
   • About 390 times stronger
7. 6.

   The Sun's pull on Earth (long) and its tidal effect (short). The Sun pulls on Earth about 177 times harder than the Moon, yet its tides are about half as big. Why, by Milo's reading (NOAA)?

   • Tides depend on distance cubed, which shrinks the Sun's effect
   • The Moon has more mass than the Sun
   • The Sun's gravity cannot reach the oceans
   • Tides follow gravity, which falls as distance squared

8. Moon distance (NASA)

   Point	Distance (km)
   perigee	363,300
   apogee	405,500

9. 7.

   The Moon is 363,300 km away at perigee and 405,500 km at apogee (NASA). How much stronger is its tidal force at perigee, by Noah's math?

   • About 1.25 times stronger
   • It is weaker at perigee
   • About 1.12 times stronger
   • About 1.39 times stronger
10. 8.

    Moon orbit diagram with perigee and apogee marked. When are tidal ranges larger than average, by Pia's reading (NOAA)?

    • When the Moon is at perigee, closest to Earth
    • When the Moon is at apogee, farthest away
    • On cloudy days
    • In the spring season
11. 9.

    At first quarter Moon, why are tides moderate (neap), by Zee's reading (NOAA)?

    • The Sun and Moon line up
    • The Sun's tide is at a right angle and partly cancels the Moon's
    • It is winter at first quarter
    • The Moon is closest then
12. 10.

    Moon-phase calendar starting at new Moon on Monday. A spring tide comes with Monday's new Moon. About when is the next spring tide, by Ari's reading?

    • About two months later
    • About one week later, at first quarter
    • Next spring
    • About two weeks later, at full Moon