# Physics question

#### richiesmasher

##### Junior Member
Hey i know this is a math site but IM struggling with a not too difficult physics question, so I didn't know where else to put this if there's anyone here who's good and has knowledge of physics please help

The qustion says

State the nature of the unbalanced force which is responsible for the circular motion in the following:

(i) A Simple Pendulum
(ii)The earth moving around the sun
(iii)Clothes rotating in a spin dryer
(iv)A car travelling around a bend
(v) An electron moving around the nucleus in an atom

For the first one I have tensional force
For the second one I have gravitational force

But for the others I'm unsure, I was thinking wait why don't I put centrifugal force for all?

But then i realized thats the resulting force of the motion, they want the nature of what's causing it, so for the others I'm unsure.

If I was to guess for 4 and 5, I would say frictional force and Nuclear force but for number 3 not sure at all.

#### Subhotosh Khan

##### Super Moderator
Staff member
Hey i know this is a math site but IM struggling with a not too difficult physics question, so I didn't know where else to put this if there's anyone here who's good and has knowledge of physics please help

The qustion says

State the nature of the unbalanced force which is responsible for the circular motion in the following:

(i) A Simple Pendulum
(ii)The earth moving around the sun
(iii)Clothes rotating in a spin dryer ....... Normal force from the spinning dryer wall
(iv)A car travelling around a bend
(v) An electron moving around the nucleus in an atom

For the first one I have tensional force
For the second one I have gravitational force

But for the others I'm unsure, I was thinking wait why don't I put centrifugal force for all?

But then i realized thats the resulting force of the motion, they want the nature of what's causing it, so for the others I'm unsure.

If I was to guess for 4 and 5, I would say frictional force and Nuclear force but for number 3 not sure at all.
.

#### richiesmasher

##### Junior Member
Oh thanks Subhotosh, yes that makes sense, the normal reaction force would be responsible indeed!

#### marshall10488

##### New member
Hey i know this is a math site but IM struggling with a not too difficult physics question, so I didn't know where else to put this if there's anyone here who's good and has knowledge of physics please help

The qustion says

State the nature of the unbalanced force which is responsible for the circular motion in the following:

(i) A Simple Pendulum
(ii)The earth moving around the sun
(iii)Clothes rotating in a spin dryer
(iv)A car travelling around a bend
(v) An electron moving around the nucleus in an atom

For the first one I have tensional force
For the second one I have gravitational force

But for the others I'm unsure, I was thinking wait why don't I put centrifugal force for all?

But then i realized thats the resulting force of the motion, they want the nature of what's causing it, so for the others I'm unsure.

If I was to guess for 4 and 5, I would say frictional force and Nuclear force but for number 3 not sure at all.
iv) friction of tyres against the road
v) electromagnetic force

#### j-astron

##### Junior Member
But for the others I'm unsure, I was thinking wait why don't I put centrifugal force for all?
It's actually a centripetal force for all of them (centripetal means "pointing towards the centre"). A centrifugal force (literally "centre-fleeing", or pointing away from the centre) is only apparent in the reference frame of the rotating object, which is not an inertial reference frame (i.e. one where Newton's first law is obeyed). We like to stick to inertial frames of reference (in this case meaning non-rotating frames of reference), because the laws of physics seem to be the same in all of them.

But then i realized thats the resulting force of the motion, they want the nature of what's causing it, so for the others I'm unsure.
If I was to guess for 4 and 5, I would say frictional force and Nuclear force but for number 3 not sure at all.
The force keeping the car going around the bend is indeed friction.

The force keeping the electron bound to the nucleus is the electromagnetic force, which is the force that causes opposite electric charges to be attracted to each other. It's not the nuclear force, which is something else. In fact there are two kinds of nuclear forces, the strong nuclear force (which keeps protons and neutrons together in a nucleus), and the weak nuclear force which...something something beta decay. https://xkcd.com/1489/

#### marshall10488

##### New member
It's actually a centripetal force for all of them (centripetal means "pointing towards the centre"). A centrifugal force (literally "centre-fleeing", or pointing away from the centre) is only apparent in the reference frame of the rotating object, which is not an inertial reference frame (i.e. one where Newton's first law is obeyed). We like to stick to inertial frames of reference (in this case meaning non-rotating frames of reference), because the laws of physics seem to be the same in all of them.

The force keeping the car going around the bend is indeed friction.

The force keeping the electron bound to the nucleus is the electromagnetic force, which is the force that causes opposite electric charges to be attracted to each other. It's not the nuclear force, which is something else. In fact there are two kinds of nuclear forces, the strong nuclear force (which keeps protons and neutrons together in a nucleus), and the weak nuclear force which...something something beta decay. https://xkcd.com/1489/
Centrifugal force doesn't actually exist, it is a phantom force. It is the object trying to continue on its current vector (perpendicular to the centripetal force) which would be conservation of momentum and newtons law of continuing or at rest unless acted upon by a force. Without the centripetal force the object will keep going in the direction its going, as the centripetal force changes the vector (acceleration : change in speed and/or direction) the inertia is felt in an outward direction and the feeling of a centrifugal force

#### stapel

##### Super Moderator
Staff member
Hey i know this is a math site but IM struggling with a not too difficult physics question, so I didn't know where else to put this...
For physics questions, maybe try a physics forum...?

#### j-astron

##### Junior Member
Centrifugal force doesn't actually exist, it is a phantom force. It is the object trying to continue on its current vector (perpendicular to the centripetal force) which would be conservation of momentum and newtons law of continuing or at rest unless acted upon by a force. Without the centripetal force the object will keep going in the direction its going, as the centripetal force changes the vector (acceleration : change in speed and/or direction) the inertia is felt in an outward direction and the feeling of a centrifugal force
I am aware of its nature as a fictitious force. All I was saying is that, for the observer in the rotating reference frame, it does exist. As I said before, Newton's laws are not obeyed in such reference frames, unless you invoke such forces.

#### marshall10488

##### New member
I am aware of its nature as a fictitious force. All I was saying is that, for the observer in the rotating reference frame, it does exist. As I said before, Newton's laws are not obeyed in such reference frames, unless you invoke such forces.
it was more richiesmasher saying to put centrifugal for all of them that was for, but a continuation of your point

#### khobbs2

##### New member
Hey i know this is a math site but IM struggling with a not too difficult physics question, so I didn't know where else to put this if there's anyone here who's good and has knowledge of physics please help

The qustion says

State the nature of the unbalanced force which is responsible for the circular motion in the following:

(i) A Simple Pendulum
(ii)The earth moving around the sun
(iii)Clothes rotating in a spin dryer
(iv)A car travelling around a bend
(v) An electron moving around the nucleus in an atom

For the first one I have tensional force
For the second one I have gravitational force

But for the others I'm unsure, I was thinking wait why don't I put centrifugal force for all?

But then i realized thats the resulting force of the motion, they want the nature of what's causing it, so for the others I'm unsure.

If I was to guess for 4 and 5, I would say frictional force and Nuclear force but for number 3 not sure at all.
For number 1 I think it is the tension force, 2 gravitational force, 3 normal force, 4 static friction force, and 5 I am not sure.

#### mmm4444bot

##### Super Moderator
Staff member
… which is responsible for the circular motion

… [of an] electron moving around the nucleus in an atom …
Does this question make sense? Electrons do not orbit a nucleus.

#### Subhotosh Khan

##### Super Moderator
Staff member
Does this question make sense? Electrons do not orbit a nucleus.
In 1800's it did - before the issue got "clouded" first by Heisenberg. Brian Green said those "slithy toves did gyre and gimble" (or is it Lewis Carroll who said that...).