Automobile braking system and brake disk with support – car without wheelGetty

Cosmic Connections is a series that explores how our experiences here on Earth aren’t so different across the universe.

You’re cruising along the freeway when a car swerves out in front of you. You slam on the brakes. The tires squeal on the pavement under your car. You finally come to a stop, mere inches from meeting disaster. After you take a few moments to put your heart back in your chest (and let the other car speed off), you reapply the gas and nervously continue on your way.

The star of this little story is not you or the other driver, but friction. Friction is the ever-present force in our lives that slows us down, delays us, and in many cases stops us. As usual in physics, there are a half dozen ways to describe the same phenomenon, and the case is no different with friction. But perhaps the most straightforward way to understand friction is to zoom in. Way in.
A surface may appear nice and even and smooth to the unenhanced eye, but closer examination reveals imperfections. At microscopic scales jagged peaks, vast valleys, and crevices great and small dominate the minuscule landscape. The more jaggedy and craggedy the terrain down there, the more rough the surface feels to us. Now imagine rubbing two of those terrains against each other. Mountains slam into mountains or get caught in a deep valley. Roughness meets roughness. 

 
Repeat these violent encounters countless times across a surface and you can see how friction saps energy from a moving object. In the case of our story, the friction saved a couple lives: the energy of the moving car was transformed into heat on the road and the squeal of the tires themselves.
 
But that’s not the only way friction can develop, especially if we take the most generic definition of friction as “processes that slow down movement”. In that wide-eyed picture, many games can be played to slow something down, even if that thing is an entire galaxy.

The Andromeda Galaxy, capable of being braked by friction.NASA/JPL-Caltech

Yup, I said it. A galaxy. Hundreds of billions of stars, ten billion times the mass of the sun. Capable of being slowed down.
It works like this:
Imagine, for the sake of a simple example, a galaxy plowing through the vacuum of intergalactic space. It’s not alone – there are dozens and dozens of galaxies surrounding it. Again for our little example imagine those galaxies are perfectly stationary.
Freeze this scenario, with one moving galaxy and the rest stationary, in a single moment of time. Gravity acts on all the galaxies, wanting to pull them closer together. So it does. All the surrounding galaxies feel the pull of the moving one, and snuggle in just a little bit tighter.
Now advance this snapshot a little bit forward in time. Our moving galaxy has done its job and moved down the road a little bit. The galaxies that once surrounded it are now in the rear-view mirror, a little bit closer than they had before. And the road ahead of the moving galaxy is filled with the same loose collection of neighbors as it started with.
But now there’s a slight difference. The galaxies behind the moving one are now closer than they had been. Which means they exert just a little bit more gravitational influence than the ones in front. Which means the moving galaxy feels a pull to its rear: it slows down.
This effect is called dynamical friction, and is seen across the universe. And just like with your squealing tires across the pavement, it pulls energy from a moving object, slowing it down.

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Auto braking system and brake disk with assistance – automobile without wheel Getty

Cosmic Links is a series that checks out how our experiences here in the world aren’t so various throughout deep space.

You’re travelling along the highway when a cars and truck swerves out in front of you. You knock on the brakes. The tires screech on the pavement under your automobile. You lastly pull up, simple inches from satisfying catastrophe. After you take a couple of minutes to put your heart back in your chest (and let the other automobile speed off), you reapply the gas and nervously continue your method.

(*************** )The star of this little story is not you or the other motorist, however friction. Friction is the ever-present force in our lives that slows us down, hold-ups us, and oftentimes stops us. As normal in physics, there are a half lots methods to explain the very same phenomenon, and the case is no various with friction. However maybe the most simple method to comprehend friction is to focus. Method.
(*************** )A surface area might appear good and even and smooth to the unenhanced eye, however closer evaluation exposes flaws. At tiny scales rugged peaks, large valleys, and crevices terrific and little control the small landscape. The more jaggedy and craggedy the surface down there, the more rough the surface area feels to us. Now picture rubbing 2 of those surfaces versus each other. Mountains knock into mountains or get captured in a deep valley. Roughness satisfies roughness.

Repeat these violent encounters many times throughout a surface area and you can see how friction saps energy from a moving item. When it comes to our story, the friction conserved a couple lives: the energy of the moving automobile was changed into heat on the roadway and the screech of the tires themselves.

(***************** )(*************** )However that’s not the only method friction can establish, particularly if we take the most generic meaning of friction as “procedures that decrease motion”. Because wide-eyed photo, lots of video games can be played to slow something down, even if that thing is a whole galaxy.

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(******** )The Andromeda Galaxy, efficient in being braked by friction. NASA/JPL-Caltech