These resources have been reviewed and selected by STEM Learning’s team of education specialists for factual accuracy and relevance to teaching STEM subjects in UK schools.


These downloadable videos and animations are part of the multimedia package Stuff and Substance, developed by the Gatsby Science Enhancement Programme (SEP). They can be used to develop ideas relating to the intrinsic motion of particles and diffusion phenomena involving the liquid and gas states.

Due to the intrinsic translational movement of particles, samples of substances in the liquid and gas states will mix without the need for external agitation (stirring of some kind). Some students find it difficult to believe that the particles in a still volume of liquid are moving – they are happier to say the particles can be moved around. The gas state is less problematic. One animation is a formative assessment task which links particle diagrams to a diffusion experiment involving a coloured and colourless liquid. The video shows the classic diffusion experiment using ammonia and hydrogen chloride (evaporating from concentrated solutions). The second animation can be used to explain the difference between intrinsic motion of individual particles and bulk movement caused by external agitation.

These video and animation files form part of the resources in the section Diffusion in the Stuff and Substance multimedia package, which provides a series of interactive pages that can be used by teachers or students in the classroom.

Please note: From 2021, Adobe has discontinued support for Flash player and as a result some interactive files may no longer be playable. As an alternative method to accessing these files a group of volunteers passionate about the preservation of internet history have created project Ruffle ( Ruffle is an entirely open source project that you can download and run many interactive Flash resources. For further information regarding STEM Learning’s policy for website content, please visit our terms and conditions page.

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