# Achieving the speed of light at the end of a whip

• idktbh1
In summary, the conversation is about the possibility of a whip reaching the speed of light with enough energy and length. However, it is scientifically proven that the end of an object, including a whip, cannot exceed the speed of light due to the laws of relativistic mechanics. The material of the whip is not a factor in this limitation. The conversation also discusses the concept of phase velocity and the limitations of material at high speeds. The conversation concludes with the explanation of why a whip cracks and the reason behind the sonic boom.f

#### idktbh1

Is there a equation for the speed at the end of the whip.
is there a consistent way to calculate how fast the tip of the whip will be including constant velocity and trajectory or is it chaotic.
Im new to physics and had a thought that with enough legnth and power a wiphs end colud reach the speed of light without using infinate energy... i don't know if that's the case . I am very invested in this any help wolud be appreciated!

My logic is that we use little energy to brake the sound barrier with a whip that it colud be possible to reach the speed of light.
The material of the whip is not a factor. Its ruled out because no material can withstand the speed of light and bend like a whip.
Im just looking for theroetical evidance for this!

The end of an object is accelerated by the part of the object next to it. If you focus on the end of a whip, its motion is governed by the laws of relativistic mechanics and cannot achieve the speed of light. There is no fundamental difference between the end of a whip and any other object.

idktbh1
The end of an object is accelerated by the part of the object next to it. If you focus on the end of a whip, its motion is governed by the laws of relativistic mechanics and cannot achieve the speed of light. There is no fundamental difference between the end of a whip and any other object.
this is very demotivating but thank you very much !

this is very demotivating but thank you very much !
All is not lost. There is still some hope.
When a wavefront crosses or is reflected by a line, the locus of the point of contact of wavefront and line, moves at a speed between that of the wavefront and infinity.
https://en.wikipedia.org/wiki/Matter_wave#Phase_velocity
"The superluminal phase velocity does not violate special relativity, because phase propagation carries no energy".

Just for info, the material at the end of the whip needs to reach twice the speed of sound in order for the 'crack' to occur.
PeroK's reply is accurate. Even given a hypothetical material of infinite strength (something physics forbids), no amount of energy could move any part of it locally at light speed. I say locally because plenty of things move faster than light non-locally. A neutrino passes between Alpha-Centauri and here at possibly faster than light as measured by either us or them, but not as measured by something in the current proximity of the neutrino. The difference is that we're all using different clocks that run at different rates due to differences in the gravitational potential of each observation point.

So with enough energy and a deep enough gravity well for your observation point (lawn-chair on a neutron star seems like a good spot, don't forget the ice tea), the speed of the whip tip can indeed exceed c, but will still not outpace nearby light moving in the same direction.

this is very demotivating but thank you very much !
Finding out news things shouldn't be 'demotivating'. Science is a journey, littered with occasions when one finds out one is wrong. Accepting that you need to modify your view according to evidence is healthy.

hmmm27 and phinds
The material of the whip is not a factor. Its ruled out because no material can withstand the speed of light and bend like a whip.
Mass'y material can't do light speed.
this is very demotivating but thank you very much !
Better now than when you've spent a fortune trying to develop a whip that can't work.

Also : spellcheck, spellcheck, spellcheck, spellcheck...

Just for info, the material at the end of the whip needs to reach twice the speed of sound in order for the 'crack' to occur.

Don't leave us hanging... why ?

Halc said:
Just for info, the material at the end of the whip needs to reach twice the speed of sound in order for the 'crack' to occur.
Don't leave us hanging... why ?
The technique seems to be to form a loop in the whip and propagate that down the ever-thinning length of the thing. So conservation of energy and momentum has the loop 'wave' moving faster and faster as the mass density of the whip goes down towards the end. The tiny sonic boom occurs if the loop can be made to move at supersonic speeds. Since it is a loop, the top of it moves at twice the speed just like the top of the wheel of a car moves at twice the speed of the car. A car does not make a sonic boom at 650 km/hr even though the top of its wheels are moving at supersonic speeds.

hmmm27
Now I am wondering if the ritual of snapping of towels in the gym was producing a sonic boom.
There was evidently no loop in the towel.

PeroK
Now I am wondering if the ritual of snapping of towels in the gym was producing a sonic boom.
There was evidently no loop in the towel.
"Evidently"? You would need a slomo camera, close up, to observe the shape at the end of a towel. Afair, the effect was best with the towel operated 'diagonally', with a corner at the end; ideal for producing a small loop and a high speed. Ahhh those were the days.

EDIT: PS, I just remembered the same sort of horseplay with my sons in the kitchen when they should have been drying dishes.

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256bits
"Evidently"?
Not the same type of loop as the 'one coil loop' ( it is kind of like a twist was put into the whip somehow ) that travels down the bullwhip that they use to analyse the bullwhip - not sure if every bullwhip user produces that type, but they ( who is they ? and why ) presume so.

The towel loop would not have that type of coil - it would be simply a halved towel where one end unfurls, and the tip of that end accelerates and the length common to the tip shortens.

So if Indiana Jones is standing on top of a train moving at 0.999999999999999999999C, calculate the gamma factors along the length of his whip from the frame of reference of his intended target bad guy standing beside the track

Not the same type of loop as the 'one coil loop' ( it is kind of like a twist was put into the whip somehow ) that travels down the bullwhip that they use to analyse the bullwhip - not sure if every bullwhip user produces that type, but they ( who is they ? and why ) presume so.

The towel loop would not have that type of coil - it would be simply a halved towel where one end unfurls, and the tip of that end accelerates and the length common to the tip shortens.
I made an assumption that the shape of the wave traveling along the whip / towel would be a simple transverse semi-loop (U shape). If anything else was meant then I would have expected a diagram as explanation. A photo image of that would constitute evidence.

256bits and hmmm27
Is there a equation for the speed at the end of the whip?

If such an equation exists, it would likely be Newtonian and ignore relativity. Getting a whip to move fast enough that relativity becomes relevant sounds... unlikely. Putting big numbers into a Newtonian equation might produce an answer faster than light. But as others here have said, what would really happen is that the energy you put into the whip would just go into making it's effective mass higher, and then tearing the whip apart.

Nice video of a whip in slow motion :

jrmichler and hmmm27