Physics marathon (hsc) (7 Viewers)

[bleakarcher]

Just curious, doesn't the rotation of the earth also cause it to bulge at the equator? So would a slower rotation speed mean the earth wouldn't bulge so much at the equator and it would be closer to the centre of the earth??

That's what I'm thinking..

 

[nerdasdasd]

=.= I think i'll post some questions that require a little bit of lateral thinking. ;/

The 7 marker did need lateral thinking.

 

[SpiralFlex]

The 7 marker did need lateral thinking.

I meant calculation questions I guess.

 

[GoldyOrNugget]

a) decrease due to lower "fling off" effect (centrifugal effect or something)
b) stays the same since the distance between the poles and centre mass is the same

Can they test this in the HSC? As far as physics course goes, . I've never seen any textbooks or notes mention the centrifugal force effects from earth's angular velocity.

 

[deswa1]

Sorry, just a question. Wouldn't a decrease in rotational velocity result in a lower radius and hence an increased value of g?

Just curious, doesn't the rotation of the earth also cause it to bulge at the equator? So would a slower rotation speed mean the earth wouldn't bulge so much at the equator and it would be closer to the centre of the earth and increase the value of g??

Yes you guys are right- at the equator there is a centripetal acceleration given by a=v^2/r which 'subtracts' from the effective value of g so when you decrease the Earth's rotational velocity, this effect is reduced and hence g increases. I think from memory the value of g is about 0.02ms-2 smaller at the equator than the poles due to this centripetal acceleration effect

 

[jennly]

what is the different between induce current, induce emf and back emf?

 

[bleakarcher]

Yes you guys are right- at the equator there is a centripetal acceleration given by a=v^2/r which 'subtracts' from the effective value of g so when you decrease the Earth's rotational velocity, this effect is reduced and hence g increases. I think from memory the value of g is about 0.02ms-2 smaller at the equator than the poles due to this centripetal acceleration effect

orite, thanks for confirming bro.

 

[someth1ng]

Assume that the Earth rotated slower than it does currently. Predict what would happen to the value of g (gravitational acceleration) at:

a) The equator
b) The poles

a. Value of g will INCREASE at the due to lower centrifuge effect, also, decrease altitude due to less centrifuge.
b. Should stay the same.

 

[Kimyia]

So should the answer be:
a) Increase because less 'fling' effect and less bulging
b) Decrease because less bulging at the equator would also means the poles would be less flattened so would end up being further away from the centre of the earth (not in relation to 'fling' effect)
Anyone confirm?

 

[deswa1]

So should the answer be:
a) Increase because less 'fling' effect and less bulging
b) Decrease because less bulging at the equator would also means the poles would be less flattened so would end up being further away from the centre of the earth (not in relation to 'fling' effect)
Anyone confirm?

It will remain unchanged at the poles because the Earth has no rotational velocity at the poles so a change in rotational velocity will have no effect.

 

[someth1ng]

So should the answer be:
a) Increase because less 'fling' effect and less bulging
b) Decrease because less bulging at the equator would also means the poles would be less flattened so would end up being further away from the centre of the earth (not in relation to 'fling' effect)
Anyone confirm?

This assumes that the poles will expand with less centrifuge but I'm not sure about that...

 

[nerdasdasd]

what is the different between induce current, induce emf and back emf?

An emf may be induced as a result of a conductor experiencing a change of flux, thus an current will also be induced as well.

Back emf is emf that a motor generates when running. This back emf opposes the current supply emf.

 

[GoldyOrNugget]

what is the different between induce current, induce emf and back emf?

emf is synonymous with potential difference, and is induced as per Faraday's law and Lenz' law. If the circuit is complete or eddy currents can form, then an induced current forms. Back emf is when an externally applied current (usually on a coil) interacts with a magnetic field as per the motor effect, but then as the coil begins to move, an emf is induced to oppose its motion by Lenz' law.

 

[Kimyia]

I was just thinking that because of the rotation, the earth bulges at the centre and flattens at the poles. So decrease the rotational speed, the equator would be closer to the centre and at the same time the poles would be further away becaues they are flattened less due to there being less of an ellipsoid shape?

 

[deswa1]

I was just thinking that because of the rotation, the earth bulges at the centre and flattens at the poles. So decrease the rotational speed, the equator would be closer to the centre and at the same time the poles would be further away becaues they are flattened less due to there being less of an ellipsoid shape?

Maybe... I'm not 100% sure tbh- you might be looking at it too deeply but idk. I'm interested to see what others think of this

 

[iBibah]

I was just thinking that because of the rotation, the earth bulges at the centre and flattens at the poles. So decrease the rotational speed, the equator would be closer to the centre and at the same time the poles would be further away becaues they are flattened less due to there being less of an ellipsoid shape?

This would have to be true because the bulging at the equator is due to gravity and the rotation of earth. So if the rotation was slower, then the bulge would be less, resulting in a shorter distance from the equator to the centre, hence greater value of g. At the poles, when the bulge reduces, the poles would have to move outwards, resulting in a larger distance from the centre, hence lower value of g.

 

[bleakarcher]

Do any of you guys know the name of this effect where the Earth bulges because of its rotational velocity? Want to look into it.

 

[clarg]

I was just thinking that because of the rotation, the earth bulges at the centre and flattens at the poles. So decrease the rotational speed, the equator would be closer to the centre and at the same time the poles would be further away becaues they are flattened less due to there being less of an ellipsoid shape?

This is what I thought - Does the rotational velocity not result in an increase in eccentricity of the Earth's ellipse? If this is the case surely the equator becoming closer to the centre of gravity will be counterbalanced by the poles becoming further away - otherwise there is an increase in Earth's density or a decrease in mass which does not happen.

It's easier to just think of an ellipse becoming more circular, as you squash the x axis in, the y axis increases.

Edit: And just to be clear, v is low enough to avoid relativistic effects lol

 

[iBibah]

Do any of you guys know the name of this effect where the Earth bulges because of its rotational velocity? Want to look into it.

Not sure if it has a name, though a quick search online will give a decent explanation.

Earth's Shape

Earth's circumference and diameter differ because its shape is classified as an oblate spheroid or ellipsoid, instead of a true sphere. This means that instead of being of equal circumference in all areas, the poles are squished, resulting in a bulge at the equator, and thus a larger circumference and diameter there.
The equatorial bulge at Earth's equator is measured at 26.5 miles (42.72 km) and is caused by the planet's rotation and gravity. Gravity itself causes planets and other celestial bodies to contract and form a sphere. This is because it pulls all the mass of an object as close to the center of gravity (the Earth's core in this case) as possible.

Because Earth rotates, this sphere is distorted by the centrifugal force. This is the force that causes objects to move outward away from the center of gravity. Therefore, as the Earth rotates, centrifugal force is greatest at the equator so it causes a slight outward bulge there, giving that region a larger circumference and diameter.

 

[RishBonjour]

I was just thinking that because of the rotation, the earth bulges at the centre and flattens at the poles. So decrease the rotational speed, the equator would be closer to the centre and at the same time the poles would be further away becaues they are flattened less due to there being less of an ellipsoid shape?

I guess you could say that, But I'm not really too sure about the whole "bulging" thing.
As something1 and I said, it probably has more to do with the centrifugal effect.
edit: just realised i said "value of g decrease" -I meant increase due to less fling off

Yes please, no long responses. just some nice phy questions.

Can they test this in the HSC? As far as physics course goes, . I've never seen any textbooks or notes mention the centrifugal force effects from earth's angular velocity.

centrifugal force itself is not really a *"force"- its a fictitious force so I avoided that word in all my tests, I just say "fling off"*
And you could definitely talk about that in HSC, along with things you could read off the equations e.g. altitude, mass of celestial body etc*

Just wondering:
- When AC generator feeds current into an external circuit, back emf is induced in the external circuit right? since the AC is constantly changing--> change in flux--> emf. But for DC, the current remains constant, hence no back emf?