Floating, Sinking and Upthrust · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why boats float and nails sink

Science · Forces & Motion · ages 8-9
Name ______________________   Date ____________

  1. How do your arms feel in the bath, and why?

    • Light, because the water pushes up
    • Heavy, because the water pushes down
    • The same as in the air

  2. What name do we give the upward push of water?

    • Downpull
    • Upthrust
    • Sidepush

  3. Water pushes up on things that sink as well as things that float.

    Circle one:   True   False

  4. What happens as you lower a floating ball slowly into water?

    • Push grows to match weight
    • The push shrinks to nothing
    • The water gets weaker

  5. A log floats but a coin sinks. Why?

    • The log is colder than the coin
    • The coin is bigger than the log
    • Packing decides float or sink

  6. A clay ball sinks. You reshape the same clay into a wide bowl and it floats. Why?

    • The clay became lighter stuff
    • The water disappeared
    • The bowl pushes aside more water, so the push grows

  7. Dan says the nail sinks because steel is heavy, and the ship floats because ships use light stuff. What is his mistake?

    • Both are the same steel; shape and air inside decide
    • Steel changes weight in ships
    • Nails are hollow

  8. You test an empty sealed bottle and the same bottle filled with sand. Which floats?

    • The bottle filled with sand
    • The empty sealed bottle, full of air
    • Both sink the same way
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Why boats float and nails sink W1-mt_TJI95Ot-qQ-s1

  1. Light, because the water pushes up · The water holds you up, so your arms feel light.
  2. Upthrust · Upthrust is the name for the upward push of water.
  3. True · The push is always there, even for things that sink.
  4. Push grows to match weight · More of the ball goes under, and the push grows with it.
  5. Packing decides float or sink · Float or sink is about packing, not just weight.
  6. The bowl pushes aside more water, so the push grows · The wide bowl shifts more water, so it earns a bigger push.
  7. Both are the same steel; shape and air inside decide · Same stuff, different shape. The hollow ship traps air.
  8. The empty sealed bottle, full of air · Sealed air makes the bottle light for its size, like a ship.
Worksheet · LightMySky