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Newton's Laws and Solar Power
Name: Kristi
Status: Student
Age: 14
Location: N/A
Country: N/A
Date: N/A
Question:
How can i build a solar powered vehicle using Newton's
third law?
Replies:
Several science-fiction novels have described this idea pretty well.
The only one I can name right off is "The Mote in God's Eye" by Larry
Niven and Jerry Pournelle. You take a huge sail, miles across, made
out of flimsiest material, and give it a mirror coating. Then you take
it out in space and aim the sun at it. Light carries momentum, and
after you've reflected light, it carries an equal amount of momentum in
the other direction. Newton's Third says somebody must now have twice
the original momentum of the light that got reflected. That would be
you, if you're clever enough to hold on to the light sail.
If you want to build a solar-powered car, this would not be a good
strategy for several reasons, one of which is that you'd only be using
the light's momentum. It would be better to absorb the light, then
you'd get the energy along with the (relatively negligible) momentum.
Tim Mooney
I assume you mean a vehicle that rolls around on earth, like a toy car.
Newton's 3rd law just says that if you push one way, you have to push onto
something. And that something is pushing back. So if your solar powered
car had wheels, that were driven with an electric motor, which in turn was
run from solar cells and electricity, this would do. The wheels are pushing
on the ground, the ground pushes back on the wheels, and pushes the car
forward. It would all the powered by the solar energy that runs the motor,
just not directly, but thru electricity.
S. Ross
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Update: June 2012
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