Try these

1. If water flows, then what holds sandcastles together?
2. Sunset – shorter or longer waves scattered?
3. Speed of sound in mph?
4. A practical use for capillary action?
5. What’s cavitation? Common with foils.
6. Common name for polytetrafluoroethene?
7. How much taller is the Eiffel Tower in summer?

13 comments for “Try these

  1. Distant Relative
    August 19, 2019 at 18:17

    1. Summat to do with the surface tension of the water.
    6. PTFE
    7. About 15 cms.

  2. Luther Burgsvik
    August 19, 2019 at 18:52

    1. The sugary fluid from diacarded fizzy drinks, ice cream and sweets found at the seaside…
    4. Any kind of painting with brushes.
    5 . I think that’s the process where tiny bubbles are created by a rotating propellor blade and consequently give it surface damage in the form of pitting. If I recall, sonar detects cavitation caused by propellors on submarines.
    7. Guesstimate ~5cm. I think the Firth of Forth bridge expands and contracts by a metre or so over the course of a year.

  3. Mark in Mayenne
    August 19, 2019 at 18:57

    6 polythene
    2 short
    4 growing trees
    5 small pockets of vacuum

  4. Robbo
    August 19, 2019 at 19:10

    3. about 900, but it varies with air pressure, therefore altitude, weather affect it

  5. rapscallion
    August 19, 2019 at 19:57

    3. Depends through what medium. It travels at 343 m/s in air; 1,480 m/s in water (4.3 times as fast as in air); and at 5,120 m/s in iron
    5. Bubbles caused by the rotary action of a propellor. At depth and depending on prop speed this cavitation is detectable
    6. PTFE

  6. Charles
    August 19, 2019 at 22:16

    1 Gravity
    4 Capillaries
    5 The creation of cavities

  7. Stephen Bayliss
    August 20, 2019 at 21:48

    3 767mph at sea level
    4 any oil lamp

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