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?

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

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

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

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

   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 390 times stronger
   • About 27 million times stronger
   • About 177 times stronger
   • About 0.46 times as strong
6. 5.

   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)?

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

7. Moon distance (NASA)

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

8. 6.

   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 1.39 times stronger
   • About 1.25 times stronger
   • About 1.12 times stronger
   • It is weaker at perigee
9. 7.

   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
   • In the spring season
   • On cloudy days
   • When the Moon is at apogee, farthest away
10. 8.

    At full Moon, the Sun and Moon are on opposite sides of Earth. Why is that still a spring tide, by Tala's reading?

    • The Sun's bulge sits across and cancels
    • Opposite sides cancel, so tides are small
    • Their bulges line up along one line and add together
    • Full Moonlight lifts the water
11. 9.

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

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

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