Monday, January 24, 2022

Media Reporting Failed Basic Central Force Motion Mechanics

This news report on The Telegraph written by Joe Pinkstone about the James Webb Space Telescope reaching its final position has a basic flaw that should be easily spotted by any intro physics student who has understood basic central force/circular motion topic.

It will stay at its current position, Lagrange 2 (L2), for its entire operational lifespan, which is expected to be around 20 years. L2 is a gravitational stable point on the other side of the Earth from the Sun, where the pull of the two bodies cancels out.

No, the pull due to the Earth and the Sun does NOT "cancels out", because if it does, then there is no centripetal force to keep the telescope to orbit around the sun! 

Rather, this is the location where the sum of the gravitational forces from the Sun and the Earth provides just the right centripetal force to keep the telescope in orbit around the Sun at the same angular speed as the Earth. It will always be on the opposite side from the Sun with respect to the Earth. You can read more explanation on what is this Lagrange2 (L2) point at the NASA website here.

This is the type of mistake that we expect to see in General Physics classes, not in major news media.


1 comment:

StevenG said...

Neither is L2 a stable point