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# Centripetal Force PHYSICS Help watch

1. "The Earth has a radius of 6400 km. Scales on the Equator and at the North pole give different readings for weight. If a person has a weight of 700 N, calculate the reading on the scale at:

a. the North pole
b. the Equator"

The answer says there is no centripetal force at the north pole and leads on from there but I don't understand how there isn't a centripetal force - wouldn't it be acting straight downwards?? and then how would you even calculate when you don't have a time...
2. (Original post by MrToodles4)
"The Earth has a radius of 6400 km. Scales on the Equator and at the North pole give different readings for weight. If a person has a weight of 700 N, calculate the reading on the scale at:

a. the North pole
b. the Equator"

The answer says there is no centripetal force at the north pole and leads on from there but I don't understand how there isn't a centripetal force - wouldn't it be acting straight downwards?? and then how would you even calculate when you don't have a time...
1. The centripetal force is the force needed to make a mass move along a particular curved path, such as a circle or ellipse. So if a body isn't moving along such a curve, you don't usually use the term "centripetal" for any forces acting on it. E.g. at the North pole, gravity acts on the body, but it isn't moving on a curve (it's spinning on a point) so the term isn't appropriate.

2. If someone is standing on the equator, the forces acting on him are weight W and the normal reaction at the ground R. The vector sum of these must provide the centripetal force required to ensure that he moves along with the earth, travelling roughly in a circle of radius 6400 km, at a rate of 1 revolution per 24 hours.

Can you carry on?
3. (Original post by atsruser)
1. The centripetal force is the force needed to make a mass move along a particular curved path, such as a circle or ellipse. So if a body isn't moving along such a curve, you don't usually use the term "centripetal" for any forces acting on it. E.g. at the North pole, gravity acts on the body, but it isn't moving on a curve (it's spinning on a point) so the term isn't appropriate.

2. If someone is standing on the equator, the forces acting on him are weight W and the normal reaction at the ground R. The vector sum of these must provide the centripetal force required to ensure that he moves along with the earth, travelling roughly in a circle of radius 6400 km, at a rate of 1 revolution per 24 hours.

Can you carry on?
So basically what you're saying is there is a centripetal force at the equator but not at the north pole - since that is a point of rotation?
4. (Original post by MrToodles4)
So basically what you're saying is there is a centripetal force at the equator but not at the north pole - since that is a point of rotation?
The north pole is a point on the axis of rotation - I don't think that the term "point of rotation" is meaningful. Apart from that: yes.

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