Newton's Laws, not sure which law this is, also FBD

[apst]

hello flyingpig.the figure is ok.but you did not mention whether the 3 contact surfaces are frictionless or not.if the surfaces are also frictionless:
consider m3 first.the forces on it are its weight and the reaction offered by m2.thats all.there is no other force on it.these 2 act in the same line in the opposite direction at the same point.reply if you understand this and i will explain about the others.i am a new user and i don't know how to get the figure drawn.

 

[vela]

Yes, that's what I am getting at. The centripetal is "real", yet we don't put it on a FBD because sum of the normal force and gravity turns out to be the same.

Say you were just looking at a block on an incline. You identify the forces on the block: the weight, the normal force, and friction. When you add those up, you get a resultant force, but you don't then draw the resultant force on the FBD and say that it's yet another force on the block, right? Yet that's essentially what you're saying you should do with the centripetal force, which is just a particular type of resultant force.

This confusion is the reason some textbooks avoid the notion of a centripetal force and stress the concept of centripetal acceleration instead. When an object undergoes circular motion, it has a centripetal acceleration that's due to the forces acting on it. In your Ferris wheel example, the weight and normal force add up to give you a centripetal acceleration equal to v²/r, which you know you have because you're moving in a circle.

 

[flyingpig]

Say you were just looking at a block on an incline. You identify the forces on the block: the weight, the normal force, and friction. When you add those up, you get a resultant force, but you don't then draw the resultant force on the FBD and say that it's yet another force on the block, right? Yet that's essentially what you're saying you should do with the centripetal force, which is just a particular type of resultant force.

This confusion is the reason some textbooks avoid the notion of a centripetal force and stress the concept of centripetal acceleration instead. When an object undergoes circular motion, it has a centripetal acceleration that's due to the forces acting on it. In your Ferris wheel example, the weight and normal force add up to give you a centripetal acceleration equal to v²/r, which you know you have because you're moving in a circle.

Is there a reason why we don't treat it as so? I mean if we were to find the sum of acceleration in circular we add up the tangenital acceleration (which is very real) and the centripetal acceleration as vectors to form a resultant vector. In that case we are treating the centripetal acceleration as a real thing.

I am interchanging acceleration and force here because they are proportionally related.

This also brings me to another question, is centrifuge force an example of Newton's Third Law?

 

[Doc Al]

Is there a reason why we don't treat it as so?

Do you mean is there a reason why we don't treat 'centripetal force' as if it were another force in addition to gravity and the normal force? (In your Ferris wheel example.) Sure: If you did, you'd be counting it twice.

I mean if we were to find the sum of acceleration in circular we add up the tangenital acceleration (which is very real) and the centripetal acceleration as vectors to form a resultant vector. In that case we are treating the centripetal acceleration as a real thing.

Centripetal acceleration is real.

I am interchanging acceleration and force here because they are proportionally related.

Don't do that.

It's really simple. Newton's 2nd law says ΣF = ma. ΣF means add up the actual forces acting on the body; a is the actual acceleration. For uniform circular motion, a = a_c.

This also brings me to another question, is centrifuge force an example of Newton's Third Law?

Not sure what you mean, but no.