# Weight before/after change in rotation Speed

## Homework Statement

How would the weight of a person in some place (48 North and 123 West) change if the rotation rate increased so a day was 3 hours long?

F=ma

## The Attempt at a Solution

rude man
Homework Helper
Gold Member
Sum of forces on the person = 0 since he's not going anywhere (hint: there are 3 terms in the equation, and yes, it's basically F = ma, except if you're going to derive evbrything you need from that one equation, remember that F and a are vectors, not just scalars).

Yes, I understand that F=ma = 0 since the person will not move. Now the three terms that come into play... would the centrifugal force help at all since the earth is rotating?

rude man
Homework Helper
Gold Member
Yes it would. Since gravitational attrcation is constant, irrespective of rotational speed, what force do you think has to change so the three add up to zero?

You are working in a frame fixed to the earth which is a rotating object hence you are in a rotating frame. Which means that you need to use fictious forces. You need the centrifugal force. The coriolis force is tangent to the earths surface... Calculate the component of the centrifugal force normal to the surface of the earth...