Thursday, 21 May 2009

Support at the speed of light

If you're ever feeling down and in need of an uplifting thought, try this science-inspired contemplation. It occurred to me yesterday as I was seeking consolation after a rather acute disappointment.

The Earth's gravity pulls on us to the tune of almost 10 m/s/s. In other words, if it were unopposed, every second it would accelerate us downwards 10 metres per second faster. But fortunately, we have a very supportive ground to keep us up. Remember Newton's third law of motion? Every action has an equal and opposite reaction. So that 10 m/s/s downward pull is counteracted by a 10 m/s/s supportive force holding us up.*

Now, imagine we had that 10 m/s/s support out in space, where there was no gravity to counteract it. How fast would you go?

Well, the speed of light is just shy of 300 million metres per second, so after 30 million seconds, one gravity of acceleration would get you to the speed of light.

And how long is 30 million seconds, you ask?

Just shy of a year: 353 days.

Think about that. Every year, the ground under you supports you with enough force to get you to the speed of light.


* For the pedants in my audience, yes, I know that force and acceleration are two different things. But for the purpose of this contemplation, the differences are immaterial, and to pedantically point them out would distract from the point of the contemplation.

Photo credits:
Earth photo from the Great Expectations blog, probably public domain.

Millennium Falcon cockpit at light speed from the Common Defense blog, almost certainly copyright Lucasfilm, fair use.

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