do the blue ball conserve angular momentum or is the representation wrong?

Boris said:

do the blue ball conserve angular momentum or is the representation wrong?

makes me dizzy.

I think the blue balls do, but the red balls don’t.

personally i don’t see angular momentum having any bearing. the balls go in straight lines. not circular. it is a reference frame thing i believe. there is no sideways force on any of the balls.

but i’m not sure.

sibeen said:

I think the blue balls do, but the red balls don’t.

Some balls do, some balls don’t
Some balls need a lot of loving and some balls don’t

+ Waits for Mythbusters to test it +

Grant and Tory can shoot at each other, Kari can come to my house.

Rule 303 said:

+ Waits for Mythbusters to test it +

Grant and Tory can shoot at each other, Kari can come to my house.

Great minds do think alike.

Rule 303 said:

+ Waits for Mythbusters to test it +

Grant and Tory can shoot at each other, Kari can come to my house.

Only needs two people – Adam and Jamie would get that gig.

party_pants said:

Only needs two people – Adam and Jamie would get that gig.

I think Adam and Jamie are necessary for the show to go on. Grant and Tory, however, can be culled without major risk to the series.

Rule 303 said:

+ Waits for Mythbusters to test it +

Grant and Tory can shoot at each other, Kari can come to my house.

But…but…but, she’s a ranga!

:)

Boris, I do wish I could slow the simulation down, but why doesn’t the ball have any sideways force applied?

The ‘straight line’ velocity of the balls appears to be approximately three times the angular velocity. Not a huge difference.

Mythbusters did an episode on this, but they used real bullets and human speeds. Orders of magnitude difference.

I see mythbusters is getting a workout.

They did an episode on this. Whether you could curve a bullet? The answer was no, but as stated in my previous post, there is at least an order of magnitude difference.

they could do it with paintball perhaps?

but why doesn’t the ball have any sideways force applied?

what is applying that force? bullets travel in straight lines, ignore them dropping due to gravity. on earth long range guns take the Coriolis in to consideration but that is the earth moving not the projectile.

sibeen said:

But…but…but, she’s a ranga!

Your ticket to New Zealand is ready for collection. Please leave your ‘Heterosexual’ card at the Departures desk.

Boris said:

but why doesn’t the ball have any sideways force applied?

what is applying that force? bullets travel in straight lines, ignore them dropping due to gravity. on earth long range guns take the Coriolis in to consideration but that is the earth moving not the projectile.

OK, my reductio ad absurdum argument was just about to use the flight of a bullet in a gravitational field. It still does.

Bullets don’t travel in a straight line on earth. They travel in a parabola. Sights are adjusted to take into account the 9.8 m/s^2 that the bullet will be effected by over the duration of its travel. The only thing stopping a bullet being effected by this force immediately after it is detonated is the length of the barrel,

sibeen said:

Boris said:

but why doesn’t the ball have any sideways force applied?

what is applying that force? bullets travel in straight lines, ignore them dropping due to gravity. on earth long range guns take the Coriolis in to consideration but that is the earth moving not the projectile.

OK, my reductio ad absurdum argument was just about to use the flight of a bullet in a gravitational field. It still does.

Bullets don’t travel in a straight line on earth. They travel in a parabola. Sights are adjusted to take into account the 9.8 m/s^2 that the bullet will be effected by over the duration of its travel. The only thing stopping a bullet being effected by this force immediately after it is detonated is the length of the barrel,

I would have said that as well but you do it so eloquently.

Bullets don’t travel in a straight line on earth….

yep. but i was ignoring the vertical displacement as the GIF only shows a plan view.

Boris said:

Bullets don’t travel in a straight line on earth….

yep. but i was ignoring the vertical displacement as the GIF only shows a plan view.

Ok, when David Scott dropped a feather and a hammer, on the moon, he was relatively stationary. If he had been rotating at a reasonable speed, what path would the feather and the hammer taken?

Boris said:

Bullets don’t travel in a straight line on earth….

yep. but i was ignoring the vertical displacement as the GIF only shows a plan view.

It would seem that in the diagram that there is a gravitational force on the blue balls due to being fired inward. The red balls seem to be fired out of this field before it takes effect.

It’s not a correct representation because it neglects the linear momentum imparted to the blues balls by the outer shooter’s motion.

sibeen said:

Boris said:

Bullets don’t travel in a straight line on earth….

yep. but i was ignoring the vertical displacement as the GIF only shows a plan view.

Ok, when David Scott dropped a feather and a hammer, on the moon, he was relatively stationary. If he had been rotating at a reasonable speed, what path would the feather and the hammer taken?

away from him.

a parabola. but that is a bad example because it doesn’t match the experiment being discussed. i don’t think.

KJW said:

It’s not a correct representation because it neglects the linear momentum imparted to the blues balls by the outer shooter’s motion.

That’s the sort of impression I got without applying mathematics.

Boris said:

a parabola. but that is a bad example because it doesn’t match the experiment being discussed. i don’t think.

so we agree that there is something amiss with the blue balls?

Boris said:

a parabola. but that is a bad example because it doesn’t match the experiment being discussed. i don’t think.

Why not? Take a view of Scott from 20 metres above his head. Same deal.

It’s not a correct representation because it neglects the linear momentum imparted to the blues balls by the outer shooter’s motion.

forgive my denseness but how should the blue balls motion change to be correct?

and thanks for showing up KJW.

:-)

I think the relative forces that propel the bullets would vastly overwhelm those that a human being could withstand. In other words, you can’t spin those people fast enough to make any measurable difference to the path of the bullets.

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

Rule 303 said:

I think the relative forces that propel the bullets would vastly overwhelm those that a human being could withstand. In other words, you can’t spin those people fast enough to make any measurable difference to the path of the bullets.

Which was ‘proved’ by Mythbusters. I’m just saying, that in the simulation shown, the red balls are obviously moving incorrectly; whilst, to me at least, the blue balls seem to following a correct path.

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

i like the first part as it is what i was thinking. i don’t “get” the second bit though.

sibeen said:

Rule 303 said:

I think the relative forces that propel the bullets would vastly overwhelm those that a human being could withstand. In other words, you can’t spin those people fast enough to make any measurable difference to the path of the bullets.

Which was ‘proved’ by Mythbusters. I’m just saying, that in the simulation shown, the red balls are obviously moving incorrectly; whilst, to me at least, the blue balls seem to following a correct path.

Whether you back the red or blue balls it is because the other looks wrong.

I said it makes me dizzy.. perhaps it is an optical illusion?

KJW said:

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

Why is the transverse velocity component wrong?

sibeen said:

KJW said:

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

Why is the transverse velocity component wrong?

Because the bullets have to leave the gun with the same transverse component as the shooter.

http://smoot.tumblr.com/page/28

this is one that also got me thinking the way i did. the broken swing example.

KJW said:

sibeen said:

KJW said:

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

Why is the transverse velocity component wrong?

Because the bullets have to leave the gun with the same transverse component as the shooter.

We’ll have no more of that kind of talk around here! We have the Second Amendment, and that’s all we need. Start putting in rules and it is a slippery slope….

KJW said:

sibeen said:

KJW said:

In the frame of reference of the observer (us), the balls do travel in a straight line, but transverse velocity component is wrong.

Why is the transverse velocity component wrong?

Because the bullets have to leave the gun with the same transverse component as the shooter.

Agreed, but I’m not sure that they don’t. The red bullets “look” wrong to me, but the transverse velocity of the tip of the gun of the central man is much less than that of the outer man, so it may be an illusion.

The Rev Dodgson said:

Agreed, but I’m not sure that they don’t. The red bullets “look” wrong to me, but the transverse velocity of the tip of the gun of the central man is much less than that of the outer man, so it may be an illusion.

Looking again, the blue bullets hit the centre, and the gun is pointing towards the centre, so that suggests that KJW is right and they have forgotten about the transverse component of the velocity.

The Rev Dodgson said:

The Rev Dodgson said:

Agreed, but I’m not sure that they don’t. The red bullets “look” wrong to me, but the transverse velocity of the tip of the gun of the central man is much less than that of the outer man, so it may be an illusion.

Looking again, the blue bullets hit the centre, and the gun is pointing towards the centre, so that suggests that KJW is right and they have forgotten about the transverse component of the velocity.

I’m not sure I follow you, Rev.

In my thought experiment, I have both protagonists standing on a merry-go-round, tossing a ball to each other. If the outer body tosses a ball to the inner, it will travel in a straight line – in their frame of reference – and so hit the centre.

Must rush off to a meeting, will look again this evening.

sibeen said:

In my thought experiment, I have both protagonists standing on a merry-go-round, tossing a ball to each other. If the outer body tosses a ball to the inner, it will travel in a straight line – in their frame of reference – and so hit the centre.

Yeah.. mine as well.

In my thought experiment, I have both protagonists standing on a merry-go-round, tossing a ball to each other. If the outer body tosses a ball to the inner, it will travel in a straight line – in their frame of reference – and so hit the centre.

which is what i have been saying.

sibeen said:

The Rev Dodgson said:

The Rev Dodgson said:

Agreed, but I’m not sure that they don’t. The red bullets “look” wrong to me, but the transverse velocity of the tip of the gun of the central man is much less than that of the outer man, so it may be an illusion.

Looking again, the blue bullets hit the centre, and the gun is pointing towards the centre, so that suggests that KJW is right and they have forgotten about the transverse component of the velocity.

I’m not sure I follow you, Rev.

In my thought experiment, I have both protagonists standing on a merry-go-round, tossing a ball to each other. If the outer body tosses a ball to the inner, it will travel in a straight line – in their frame of reference – and so hit the centre.

Must rush off to a meeting, will look again this evening.

They have different frames of reference. It’s probably less confusing if you take the blue guy off the roundabout and put him on a bicycle on a tangential path. When the bicycle touches the roundabout (and ignoring the fact that he’ll crash and fall off) it has the same velocity as the rim of the roundabout, so the bullet leaving the gun has a velocity component in the direction of the centre of the roundabout (i.e. the direction the gun is pointed), and a perpendicular component in the direction of the bicycle (or rim of the roundabout). The resultant velocity is not towards the centre of the roundabout.

The resultant velocity is not towards the centre of the roundabout.

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Boris said:

The resultant velocity is not towards the centre of the roundabout.

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Straight, in the direction of the resultant velocity at exit.

The resultant velocity is a combination of the velocity of the bullet down the barrel, and the transverse velocity of the tip of the barrel.

Straight, in the direction of the resultant velocity at exit.

so it’ll exit the barrel at an angle to the barrel?

Boris said:

Straight, in the direction of the resultant velocity at exit.

so it’ll exit the barrel at an angle to the barrel?

No, it won’t.

That’s why it will have the same transverse velocity as the tip of the barrel.

If you prefer, you can look at it from the blue persons frame of reference, in which the transverse velocity of the gun is zero, but the centre of the roundabout has a transverse velocity to the left.

Boris said:

Straight, in the direction of the resultant velocity at exit.

so it’ll exit the barrel at an angle to the barrel?

Not from the shooter’s frame of reference it won’t.

so the bullet will go straight to the centre guy?

Not from the shooter’s frame of reference it won’t.

i didn’t think that was what was meant but i like to be sure. i am not up on the maths or physics so i need a good explanation so i can follow. a picture would be better.

Boris said:

so the bullet will go straight to the centre guy?

Actually if it did that, from the POV of the shooter, the bullet would actually have to leave the barrel on an angle.

Actually if it did that, from the POV of the shooter, the bullet would actually have to leave the barrel on an angle.

see this is what i don’t get. if the gun is pointing at the centre guy and the bullet goes straight then it must hit him. are you saying this view is wrong?

Boris said:

Not from the shooter’s frame of reference it won’t.

i didn’t think that was what was meant but i like to be sure. i am not up on the maths or physics so i need a good explanation so i can follow. a picture would be better.

I’m not good at pictures but I understood when Rev said we can think about it as the shooter moving in a straight line tangential to the circle and firing at the point when the gun intersects the circle, since the velocities are identical at this point to the diagram. Then we can think about stopping the shooter and moving the target instead. Unless the shooter fires on an angle, the bullet will miss the target.

Boris said:

Actually if it did that, from the POV of the shooter, the bullet would actually have to leave the barrel on an angle.

see this is what i don’t get. if the gun is pointing at the centre guy and the bullet goes straight then it must hit him. are you saying this view is wrong?

Yep, see my last post I just made.

ok, i need a picture. thanks for explaining. i think i am getting an inkling of what happens.

>so the bullet will go straight to the centre guy?

Yes but he won’t be there any more.

Here’s a slowed-down version:

Boris said:

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Straight, but not towards the centre. The bullet velocity is the vector sum of the muzzle velocity pointing towards the centre plus the shooter’s tangential speed. So we need to draw a right angle triangle, with the muzzle speed as one leg of the triangle and the shooter’s speed on the other; the bullet’s actual speed and direction will be the hypotenuse of that triangle.

PM 2Ring said:

Here’s a slowed-down version:

Boris said:

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Straight, but not towards the centre. The bullet velocity is the vector sum of the muzzle velocity pointing towards the centre plus the shooter’s tangential speed. So we need to draw a right angle triangle, with the muzzle speed as one leg of the triangle and the shooter’s speed on the other; the bullet’s actual speed and direction will be the hypotenuse of that triangle.

The centre guy, isn’t in the centre.

roughbarked said:

PM 2Ring said:

Here’s a slowed-down version:

Boris said:

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Straight, but not towards the centre. The bullet velocity is the vector sum of the muzzle velocity pointing towards the centre plus the shooter’s tangential speed. So we need to draw a right angle triangle, with the muzzle speed as one leg of the triangle and the shooter’s speed on the other; the bullet’s actual speed and direction will be the hypotenuse of that triangle.

The centre guy, isn’t in the centre.

red will never hit blue because he’s firing at the place past where he has just been.

triangles i can understand.

PM you’d like some of the stuff on that website http://smoot.tumblr.com/page/106 there are some good mathy type animations and images. some with the mathematica code. there are nearly 800 pages so you’ll have to sift through them.

>Yes but he won’t be there any more.

…until the bullet hits him :)

Boris said:

so the bullet will go straight to the centre guy?

No, why would it? It has a transverse velocity relative to the centre guy.

No, why would it?

well it isn’t a case of why would it surely? if i am asking then i don’t understand so a comment like that isn’t going to enlighten me.

Boris said:

No, why would it?

well it isn’t a case of why would it surely? if i am asking then i don’t understand so a comment like that isn’t going to enlighten me.

It might if you read the whole thing and also considered the other comments.

If you prefer, consider the blue guy as stationary and the red guy on a bicycle. The blue guy is pointing at a stationary target, and he fires his gun just as the red guy cycles in front of it. Does the very slow bullet hit the red guy? No, he has moved on when the bullet reaches the target.

PM 2Ring said:

Here’s a slowed-down version:

Boris said:

if the gun is pointing towards the centre what shape will the trajectory of the bullet take? straight or curved?

Straight, but not towards the centre. The bullet velocity is the vector sum of the muzzle velocity pointing towards the centre plus the shooter’s tangential speed. So we need to draw a right angle triangle, with the muzzle speed as one leg of the triangle and the shooter’s speed on the other; the bullet’s actual speed and direction will be the hypotenuse of that triangle.

The slowed-down version makes it clear that the velocity of the bullet is at an angle to the gun (and that they’ve neglected the tangential component).

KJW said:

The slowed-down version makes it clear that the velocity of the bullet is at an angle to the gun (and that they’ve neglected the tangential component).

… in frame of reference of the shooter.

KJW said:

KJW said:

The slowed-down version makes it clear that the velocity of the bullet is at an angle to the gun (and that they’ve neglected the tangential component).

… in frame of reference of the shooter.

Yep, I can agree with that.

I’d just like to know where the hell PM 2Ring was last evening!

:)

sibeen said:

I’d just like to know where the hell PM 2Ring was last evening!

Having a life?

We do that occasionally. :-)

The Rev Dodgson said:

They have different frames of reference.
It’s probably less confusing if you take the blue guy off the roundabout and put him on a bicycle on a tangential path. When the bicycle touches the roundabout (and ignoring the fact that he’ll crash and fall off) it has the same velocity as the rim of the roundabout, so the bullet leaving the gun has a velocity component in the direction of the centre of the roundabout (i.e. the direction the gun is pointed), and a perpendicular component in the direction of the bicycle (or rim of the roundabout). The resultant velocity is not towards the centre of the roundabout.

This is the correct way to deal with accelerated frames of reference. Even in relativity, one examines the inertial frames of reference in which the accelerated object is at instantaneous rest.

KJW said:

The slowed-down version makes it clear that the velocity of the bullet is at an angle to the gun (and that they’ve neglected the tangential component).

… in frame of reference of the shooter.

I suppose I should do a version of this anim that doesn’t neglect the tangential component… but I’m feeling too lazy today.

sibeen said:

In my thought experiment, I have both protagonists standing on a merry-go-round, tossing a ball to each other. If the outer body tosses a ball to the inner, it will travel in a straight line – in their frame of reference – and so hit the centre.

No. In the frame of reference of the people on the merry-go-round, the ball will not travel in a straight line. Their frame of reference is not inertial and there will be a fictitious force acting on the ball.

No way in hell is that blue ball feasible

From http://xkcd.com/123/

thanks for all you input.

PM did you look through some of the smoot webpages?

But…They are not moving in relation to each other…

So aiming straight ay each other they both must hit…

However slow your balls are.

PM 2Ring said:

From http://xkcd.com/123/

Black Hat is correct and Mr Bond is wrong. CentriFUGal force is the force that Mr Bond experiences by being in a non-inertial frame of reference, while centriPETal force is the inward force keeping the ring of the centrifuge moving along a circular trajectory. However, the force that the ring of the centrifuge exerts on Mr Bond is centripetal.

Thus, what we think of as the force of gravity is in some sense a centrifugal force, while general relativity considers the upward force the ground exerts on our feet, in some sense a centripetal force.

Boris said:

PM did you look through some of the smoot webpages?

Yes, I had a quick browse; I’ll probably check it out some more. Thanks, Boris.

Mr Ironic said:

But…They are not moving in relation to each other…

So aiming straight ay each other they both must hit…

However slow your balls are.

But… they are moving in relation to each other.

Mr Ironic said:

But…They are not moving in relation to each other…

Oh yes they are!

Mr Ironic said:

But…They are not moving in relation to each other…

So aiming straight ay each other they both must hit…

However slow your balls are.

Neither are using an inertial frame of reference, the outer person is in circular motion, while the inner person is spinning. So, they will both see fictitious forces acting to curve the motion of the ball in their frame of reference. In the inertial frame of reference of an external observer, the balls trajectory will be straight.

But… they are moving in relation to each other.
—————————————————————-

They are both moving in the same vector, distance doesn’t matter.

Maybe.

the outer person is in circular motion, while the inner person is spinning.
——————————————————-

Seriously, WTF is the difference?

In the inertial frame of reference of an external observer, the balls trajectory will be straight.
_________________________

Ahhhh…. Nope.

KJW said:

the inner person is spinning.

Although the inner person, as a “point particle”, is not accelerating, the frame of reference that the inner person uses to describe the surroundings is a rotating frame of reference and therefore non-inertial.

But… they are moving in relation to each other.
——————————————————————————

I don’t see it. Please explain.

Mr Ironic said:

the outer person is in circular motion, while the inner person is spinning.
——————————————————-

Seriously, WTF is the difference?

The outer person is in accelerated motion, while the inner person is not in accelerated motion, only the frame of reference is rotating

Mr Ironic said:

In the inertial frame of reference of an external observer, the balls trajectory will be straight.
_________________________

Ahhhh…. Nope.

In an inertial frame of reference, where is the force coming from that curves the ball’s trajectory?

In an inertial frame of reference, where is the force coming from that curves the ball’s trajectory?
—————————————————————————————

If you are external… then it comes from the spin of the roundabout.

Mr Ironic said:

In an inertial frame of reference, where is the force coming from that curves the ball’s trajectory?
—————————————————————————————

If you are external… then it comes from the spin of the roundabout.

What does?

The ball from the outside person will have a tangential velocity

I guess that’s already been covered

Mr Ironic said:

In an inertial frame of reference, where is the force coming from that curves the ball’s trajectory?
—————————————————————————————

If you are external… then it comes from the spin of the roundabout.

But once the ball leaves the hand, there is no longer any interaction with the merry-go-round, so there is no force acting on the ball, and the ball will travel in a straight line.

and the ball will travel in a straight line.
————————————————————————

Yes, straight along the vector line…

The Rev Dodgson said:

Mr Ironic said:

In an inertial frame of reference, where is the force coming from that curves the ball’s trajectory?
—————————————————————————————

If you are external… then it comes from the spin of the roundabout.

What does?

OK, the force, I should have read it all.

How can a spinning roundabout apply a force to an object that isn’t touching it?

Mr Ironic said:

and the ball will travel in a straight line.
————————————————————————

Yes, straight along the vector line…

Which vector line?

How can a spinning roundabout apply a force to an object that isn’t touching it?
—————————————————

Ummm by the barrell…

Which vector line?
—————————————

The one directly between both parties.

Mr Ironic said:

How can a spinning roundabout apply a force to an object that isn’t touching it?
—————————————————

Ummm by the barrell…

But that’s not touching the ball while it’s in mid-flight.

the man in the centre can’t shoot the man on the circumference because the man on the circumference is changing his position all the time

the man in the centre doesn’t change position and hence gets hit

But that’s not touching the ball while it’s in mid-flight.
———————————————————————————-

I don’t understand why thats important.

because the man on the circumference is changing his position all the time
———————————————————————————
Not in respect to the shooter…

Mr Ironic said:

But that’s not touching the ball while it’s in mid-flight.
———————————————————————————-

I don’t understand why thats important.

Because the force on the ball is an moment-by-moment thing. The ball isn’t going to curve simply because it had a force on it in the past.

wookiemeister said:

the man in the centre can’t shoot the man on the circumference because the man on the circumference is changing his position all the time

the man in the centre doesn’t change position and hence gets hit

That’s what the animation is showing, but it’s wrong in that the man in the centre will not get hit.

if the man on the outer was on a hexagonal track how would his balls being fired perpendicular from the track into the centre travel?

if you had another similar shape with lots of sides but not circular what would the ball tracks look like then?

KJW said:

wookiemeister said:

the man in the centre can’t shoot the man on the circumference because the man on the circumference is changing his position all the time

the man in the centre doesn’t change position and hence gets hit

That’s what the animation is showing, but it’s wrong in that the man in the centre will not get hit.

I thought the man in the centre was being hit

wookiemeister said:

if the man on the outer was on a hexagonal track how would his balls being fired perpendicular from the track into the centre travel?

While the shooter remains on one side of the track, the line between ball and shooter would remain perpendicular to that side. Since the shooter is moving, the trajectory would not be perpendicular to the side.

wookiemeister said:

I thought the man in the centre was being hit

In the animation, yes, but it’s wrong

The ball isn’t going to curve simply because it had a force on it in the past.
———————————————————-

Yeah I really fail to see that.

Maybe I’m missing something…

Throw a ball up in a car, at speed, and it travels up and down with the passenger.

Why is this any different?

Mr Ironic said:

How can a spinning roundabout apply a force to an object that isn’t touching it?
—————————————————

Ummm by the barrell…

I don’t know what you mean.

Mr Ironic said:

Which vector line?
—————————————

The one directly between both parties.

But that vector is not the vector of the resultant bullet velocity.

Mr Ironic said:

The ball isn’t going to curve simply because it had a force on it in the past.
———————————————————-

Yeah I really fail to see that.

Maybe I’m missing something…

Throw a ball up in a car, at speed, and it travels up and down with the passenger.

Why is this any different?

But what does it look like from someone on the footpath as it drives by? thats the issue ;)

Mr Ironic said:

The ball isn’t going to curve simply because it had a force on it in the past.
———————————————————-

Yeah I really fail to see that.

Maybe I’m missing something…

Throw a ball up in a car, at speed, and it travels up and down with the passenger.

Why is this any different?

The speed of the car imparts a forward velocity on the ball. But we’re talking about acceleration.

I don’t know what you mean.
—————————————-

Well the barrell is moving as the the rest.

i said it earlier and i say it again: we need a picture.

;-)

btw it is barrel. i’m a printer ant a physicist so i have to be right about something in this thread.

:-)

But that vector is not the vector of the resultant bullet velocity.
——————————————-

There in lies our difference…

But what does it look like from someone on the footpath as it drives by? thats the issue ;)
—————————————————-

Well it would be curved, the slower the ball the greater the curve.

Mr Ironic said:

I don’t know what you mean.
—————————————-

Well the barrell is moving as the the rest.

As the rest of what?

The gun is moving relative to the centre of the circle. That’s why the resultant velocity of the bullet is not along the line of gun barrel.

transit of venus biscuits.

But we’re talking about acceleration.
—————————————————————-
I don’t think so.

Different speeds but naf all acceleration.

Mr Ironic said:

But that vector is not the vector of the resultant bullet velocity.
——————————————-

There in lies our difference…

Which part of the explanation of the components of the bullet’s resultant velocity do you disagree with?

Mr Ironic said:

But we’re talking about acceleration.
—————————————————————-
I don’t think so.

Different speeds but naf all acceleration.

anything in uniform circular motion is under constant acceleration.

This seems to be going in circles, so I’m going to head of at a tangent somewhere else.

Mr Ironic said:

But we’re talking about acceleration.
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I don’t think so.

Different speeds but naf all acceleration.

You said the ball’s trajectory in an inertial frame of reference would be curved. That’s an acceleration.

Dropbear said:

Mr Ironic said:

But we’re talking about acceleration.
—————————————————————-
I don’t think so.

Different speeds but naf all acceleration.

anything in uniform circular motion is under constant acceleration.

towards the centre

The gun is moving relative to the centre of the circle. That’s why the resultant velocity of the bullet is not along the line of gun barrel.
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Yeh but no but yeah.

Please reconsider.

Which part of the explanation of the components of the bullet’s resultant velocity do you disagree with?
————————————————————-
But that vector is not the vector of the resultant bullet velocity.

anything in uniform circular motion is under constant acceleration.
——————————————

Ok acceleration by change of direction, but the center moves accordingly with the outer edge.

Mr Ironic said:

The gun is moving relative to the centre of the circle. That’s why the resultant velocity of the bullet is not along the line of gun barrel.
————————————————————
Yeh but no but yeah.

Please reconsider.

Why?

Mr Ironic said:

Which part of the explanation of the components of the bullet’s resultant velocity do you disagree with?
————————————————————-
But that vector is not the vector of the resultant bullet velocity.

Why do you disagree with that?

Mr Ironic said:

anything in uniform circular motion is under constant acceleration.
——————————————

Ok acceleration by change of direction, but the center moves accordingly with the outer edge.

acceleration is acceleration

anyway the blue ball fired from the outside will have a tangential velocity and hence will not hit the guy in the middle..

You said the ball’s trajectory in an inertial frame of reference would be curved. That’s an acceleration.
—————————————————————

Why?

Mr Ironic said:

anything in uniform circular motion is under constant acceleration.
——————————————

Ok acceleration by change of direction, but the center moves accordingly with the outer edge.

What if the centre wasn’t rotating?

The Rev Dodgson said:

Mr Ironic said:

anything in uniform circular motion is under constant acceleration.
——————————————

Ok acceleration by change of direction, but the center moves accordingly with the outer edge.

What if the centre wasn’t rotating?

it wouldn’t matter the fellah in the middle doesn’t change position

Mr Ironic said:

You said the ball’s trajectory in an inertial frame of reference would be curved. That’s an acceleration.
—————————————————————

Why?

Because a body without acceleration moves in a straight line.

Alternatively, a body moving along a curve has a change of velocity, and acceleration = change of velocity/time, so it has an acceleration.

The gun is moving relative to the centre of the circle. That’s why the resultant velocity of the bullet is not along the line of gun barrel.
————————————————————
Yeh but no but yeah.

Please reconsider.

Why?
————————

Because it doesn’t make any sense to me.

Just seems like a fact made into an assumption.

Why do you disagree with that?
————————————————
Don’t things that start along a vector line continue unless another force is acted apon it?

wookiemeister said:

The Rev Dodgson said:

Mr Ironic said:

anything in uniform circular motion is under constant acceleration.
——————————————

Ok acceleration by change of direction, but the center moves accordingly with the outer edge.

What if the centre wasn’t rotating?

it wouldn’t matter the fellah in the middle doesn’t change position

Yes, obviously the rotation or not of the centre makes no difference to whether the bullet hits or not, but if the centre is not rotating the outer body is clearly moving wrt the centre, so the bullet will not hit the centre, so the bullet will not hit the centre even if it is rotating.

Mr Ironic said:

Why do you disagree with that?
————————————————
Don’t things that start along a vector line continue unless another force is acted apon it?

Yes :)

Mr Ironic said:

The gun is moving relative to the centre of the circle. That’s why the resultant velocity of the bullet is not along the line of gun barrel.
————————————————————
Yeh but no but yeah.

Please reconsider.

Why?
————————

Because it doesn’t make any sense to me.

Just seems like a fact made into an assumption.

Why doesn’t it make any sense?

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.

Mr Ironic said:

Why do you disagree with that?
————————————————
Don’t things that start along a vector line continue unless another force is acted apon it?

Yes, but the resultant velocity of the bullet is never along the direction of the barrel.

Mr ironic,

if you don’t understand why the ball will feel a tangential force, then I suggest you go sit in the gravitron for a little while, or a kids roundabout, and hang on tight …

the man on the circumference doesn’t have velocity he is being accelerated

wookiemeister said:

the man on the circumference doesn’t have velocity he is being accelerated

FMD.

wookiemeister said:

the man on the circumference doesn’t have velocity he is being accelerated

First post in this thread I clicked on tonight.

goes back to watching the footy

wookiemeister said:

the man on the circumference doesn’t have velocity he is being accelerated

What frame of reference are you using? For any inertial FOR he has continual acceleration so he can only have zero velocity for one instant.

For a fixed FOR at the centre of the circle he has constantly changing velocity of fixed magnitude and constantly changing direction.

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.
————————————-
That seems to totally contradict what KJW said.

But to be fair, I only bought into a $5.00 argument and ended up with 20 buck disagreement.

Yes, but the resultant velocity of the bullet is never along the direction of the barrel.
—————————————-
So you can curve a bullet…

Mr Ironic said:

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.
————————————-
That seems to totally contradict what KJW said.

No, it’s exactly equivalent to what KJW said.

OK.

I’m going to find a kids roundabout and throw balls at the centre…

Mr Ironic said:

Yes, but the resultant velocity of the bullet is never along the direction of the barrel.
—————————————-
So you can curve a bullet…

Why do you say that?

We are talking about adding two constant velocities. The resultant is a constant motion in a straight line, not a curve.

Mr Ironic said:

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.
————————————-
That seems to totally contradict what KJW said.

Let’s be clear. It is in the inertial frame of reference in which the shooter is at rest at the instant the bullet leaves the barrel that the velocity of the bullet is in the same direction as the gun is pointing.

Mr Ironic said:

OK.

I’m going to find a kids roundabout and throw balls at the centre…

Watch the TV thing about the journey of the Earth around the Sun from last week.

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.
————————————-
That seems to totally contradict what KJW said.

Let’s be clear. It is in the inertial frame of reference in which the shooter is at rest at the instant the bullet leaves the barrel that the velocity of the bullet is in the same direction as the gun is pointing.
———————————————————————————————

And there we were about to invest millions on poker stars…

Mr Ironic said:

The bullet moves along the barrel. The barrel has a velocity perpendicular to the direction it is pointing, so the resultant velocity cannot be in the direction of the barrel.
————————————-
That seems to totally contradict what KJW said.

Let’s be clear. It is in the inertial frame of reference in which the shooter is at rest at the instant the bullet leaves the barrel that the velocity of the bullet is in the same direction as the gun is pointing.
———————————————————————————————

And there we were about to invest millions on poker stars…

??

Let’s also be clear, if you choose an inertial FOR in which the bullet has zero velocity transverse to the barrel, the centre of the circle then has a velocity transverse to the direction of the barrel, so the result is the same.

Ok, so what’s the conculsion?

Does the center guy hit everytime or do they both miss left and right of each other?

to be honest this is all starting to sound like bullshit

They both miss

I think we are going around in circles here

geddit?

KJW said:

Neither are using an inertial frame of reference, the outer person is in circular motion, while the inner person is spinning. So, they will both see fictitious forces acting to curve the motion of the ball in their frame of reference. In the inertial frame of reference of an external observer, the balls trajectory will be straight.

This is the Coriolis effect

Boris said:

Unlike the animation in the opening post, this one is kinematically correct. This is because the direction in which the red ball is propelled is derived from the kinematics itself (the direction the blue curve leaves the yellow circle and the resuling direction of the red line), and not imposed by fiat. Putting this another way, the system has a given number of degrees of freedom and the animation fixes them to produce a unique consistent result. By contrast, the animation in the opening post has the same degrees of freedom (for the outer shooter), but attempts to fix a greater number of variables than the degrees of freedom that are available to be fixed. The particular variable that is a dependent variable rather than an independent variable is the direction the gun is pointing (which is not explicitly specified in the above animation). This lead to the inconsistency that is the violation of the conservation of linear momentum (specifically, the violation of the Galilean symmetry of the non-relativistic laws of physics, coupled with Noether’s theorem).