How do you make an abstract concept real and meaningful to your audience? It helps to first relate the concept to something specific and familiar that your audience understands. Here's how one presenter used a prop to do just that.
This presenter is an agronomist who often does presentations on soil and sustainability. When explaining wind erosion, he passes out dimes to everyone in the audience. A dime is 1/36th of an inch thick. He explains that if an acre of land loses soil equivalent to the height of a dime it would be losing 5 tons of soil per acre.
After the audience has had a moment to digest what this means, he tells them that if we lose soil beyond the thickness of that dime, it will take us over 400 years to regenerate. He then points out the obvious: we cannot afford to lose that much soil - and that is what we call sustainability.