Some textbooks still perpetuate the idea that a thing called ‘centrifugal force’ is pulling outwards on a mass being whirled around on a string; they say it’s what keeps the string taut. In fact, the string has to stay in tension in order continually to drag the mass away from its natural tendency to travel in a straight line . . .
Tie a mass on to a string. Let it hang – don’t let it swing.
There’s a tension in the cord, and that’s the clue:
There’s a serious pulling force (it is gravity, of course)
Acting outwards on the mass, away from you.
Now whirl the mass, instead, in a circle round your head:
Still a tension in the cord, I think you’ll find;
So are we right to claim there’s an outwards force again?
That depends upon the picture in your mind.
First, imagine you’re the mass (oh, you poor demented ass!);
You can feel an inwards tension from the string,
And you think, “That tension oughta make the string a little shorter,
Yet it isn’t so. Now there’s a curious thing!
It must mean, by Newton’s Laws, there must be another force
That is opposite and equal to it, see?”
You think, “Opposite direction means it’s outwards in complexion –
A centrifugal force! So QED.”
Now pretend that you can fly: go and hover in the sky.
(Someone else can do the whirling – show them how.)
From this aerial perspective you can be a force detective:
Can you see what’s going on below you now?
“Things go straight (or do not move) as though they’re travelling in a groove,
If no forces are externally exerted.”
That’s what Isaac Newton said; and, even though he’s dead,
His Laws are frequently asserted.
So, if what you’re now observing is a whirling mass that’s curving,
It’s curving ‘cos a force is hard at work.
It’s an inwards-acting traction with a centripetal action,
Acting on the mass to change its state.
So the mass is forced to swerve as it travels in its curve:
The dynamic equilibrium of flight.
Centrifugal force? A myth! Don’t believe in things like thyth!
Just release the string to prove that I am right . . .