• Question: is toothpast a solid or liquid

    Asked by acme499tet to Thomas, Michael S, Martin M, Kirsty R, Alexander dB on 20 Feb 2024.
    • Photo: Alexander de Bruin

      Alexander de Bruin answered on 20 Feb 2024:


      it’s a bit of both, probably more liquid than solid because it flows when pushes. Welcome to the world of soft matter physics/chemistry!

    • Photo: Thomas Swift

      Thomas Swift answered on 20 Feb 2024:


      It’s actually what we’d call a ‘gel’ – which is made of tiny solid particles floating in a liquid.

      The particles are so tiny however that – as far as you can look, taste and feel – it’s a new distinct thing that isn’t quite a solid and isn’t quite a liquid. It’s a bit of both and actually neither.

    • Photo: Martin McCoustra

      Martin McCoustra answered on 20 Feb 2024:


      Thomas is right… it is both and displays properties of both liquids and solids as a gel.

    • Photo: Michael Schubert

      Michael Schubert answered on 26 Feb 2024:


      Like Thomas said, it’s neither, but has properties of both! Gels (and some other substances) are a type of substance called “colloids,” which means that one substance is mixed throughout another substance. In the case of toothpaste, it’s those tiny solid particles floating in a liquid. Another example of a colloid is milk, which is a mixture of fat particles floating in water.

    • Photo: Kirsty Ross

      Kirsty Ross answered on 14 Mar 2024:


      It is both, and neither. It is actually similar to glass from that point of view. There are some very old panes of glass where the bottom is thicker than the top, as it has flowed (incredibly slowly) down under gravity.

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