Just because we can’t see something doesn’t mean it isn’t be pushing or pulling something else around. And did you know that weight is a force just like pushing or pulling? If you don’t believe that, just have somebody bigger than you sit on you — very carefully. You’ll change your mind in a hurry.

Even germs weigh something — just not very much compared to people. Germs can push or pull things, too — just not very hard compared to us. In fact, even things inside germs can push and pull other things around inside the germs. We call all this weak pushing and pulling and weighing invisible forces.

We think about invisible forces differently than everyday forces. For instance, how much something very small weighs isn’t so important for understanding how it works. But, a kind of stickiness called friction that slows down moving things is a big deal. In our world, one push is enough to get a ball rolling across a smooth table. But if you push small things inside a germ cell, they stop moving as soon as the pushing stops.

Tom Perkins is a scientist at JILA. He wants to learn how to measure tiny invisible forces. He wants to measure them with DNA! DNA is stretchy and acts like a spring. It is made in cells and in science labs. Almost cells have DNA. That’s because DNA contains all the information needed to make a person, a pine tree, a stink bug, or a germ. That’s why people think of DNA as the blueprints for life.

Tom Perkins thinks DNA is going to be a great tool for measuring invisible forces.

An artist drew this picture so you could see how measuring forces we can see isn’t so very different from measuring invisible forces. You just need the right tool for the job.

On the right, a simple spring balance measures the weight of an apple. On the left, a short strand of DNA measures the weight of an E. coli bacterium. E. coli is a germ that can cause a nasty stomach flu. —Julie Phillips

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