Are there waves that go up and down without going below zero displacement?

[danielhaish]

weave is change in something. and I always see harmonics wave that looks like this there is some normal value let's say the height of the water then the height of the water become higher then normal and then lower like that

But do there are an harmonics waves in physics that just going up and then down but don't go lower then the normal value ? something like this

Or even something like that

 

[kuruman]

A full wave rectifier takes a signal that looks like what you have in the first figure and converts it to a signal that looks like what you have in the second figure.

 

[danielhaish]

i am not taking about digital signal i mean if there is any weave in nature that behave like that

 

[kuruman]

If I understand your question correctly, you are asking whether there is full rectification occurring without human intervention. I don't know of any cases.

 

[berkeman]

i am not taking about digital signal i mean if there is any weave in nature that behave like that

(Note -- I fixed up your thread title a bit.)

I can think of at least one system that might meet your requirements. Take a metal ball attached to a coil spring, and run a metal shaft up through the coil spring until it makes contact with the ball in the relaxed condition of the spring. Then pull the ball away from the rod to stretch the spring to store energy in the stretched spring + ball system.

Then release the ball. What kind of motion do you think the ball will execute? Assume perfectly elastic collisions when the ball bounces off of the rod...

 

[danielhaish]

Thanks it too bad that we don't learn those things because this kind of waves change a lot the calculation of infiltration

 

[DaveC426913]

Infiltration?

 

[kuruman]

(Note -- I fixed up your thread title a bit.)

I can think of at least one system that might meet your requirements. Take a metal ball attached to a coil spring, and run a metal shaft up through the coil spring until it makes contact with the ball in the relaxed condition of the spring. Then pull the ball away from the rod to stretch the spring to store energy in the stretched spring + ball system.

Then release the ball. What kind of motion do you think the ball will execute? Assume perfectly elastic collisions when the ball bounces off of the rod...

The plot of position vs. time would reproduce what OP wants, but where is the wave? I thought of and rejected a ball bouncing (elastically) off the floor exactly for that reason.

 

[danielhaish]

it a wave

where is the wave

I think that the wave is the spreading of the motion along the spring

 

[sophiecentaur]

The simplest waves exist in a 'linear medium' where the displacement and the restoring force are proportional. That sustains a symmetrical waveform (sinusoidal is the simplest example) but in nature there are many examples where the motion of the medium is limited in one direction and the wave gets lop sided. A ball on a spring that bounces against the floor is an example (as suggested above). In fact every natural system has limits to the values of the variables and for high enough amplitude waves, 'something' hits the end stop.

Sound waves are pretty well behaved (can be pure sinsoids) under normal conditions but (of course) the pressure fluctuations in the sound can't get lower than zero and the rate of movement of the air can't exceed the speed of sound and a very LOUD sine wave can't be sustained. Waves on water may look like nice sine waves bu they go 'peaky' went the amplitude is high and when the water is shallow. The sea bed is the limit to the trough depth.

@danielhaish I suspect that y our question is not yet formed completely in your mind. Perhaps you will find that the content of this thread will help you rephrase your question. Is there anything here that's helped you so far?

 

[A.T.]

it a wave

Seems like you are confusing waves with general periodic motion.

 

[danielhaish]

The simplest waves exist in a 'linear medium' where the displacement and the restoring force are proportional. That sustains a symmetrical waveform (sinusoidal is the simplest example) but in nature there are many examples where the motion of the medium is limited in one direction and the wave gets lop sided. A ball on a spring that bounces against the floor is an example (as suggested above). In fact every natural system has limits to the values of the variables and for high enough amplitude waves, 'something' hits the end stop.

Sound waves are pretty well behaved (can be pure sinsoids) under normal conditions but (of course) the pressure fluctuations in the sound can't get lower than zero and the rate of movement of the air can't exceed the speed of sound and a very LOUD sine wave can't be sustained. Waves on water may look like nice sine waves bu they go 'peaky' went the amplitude is high and when the water is shallow. The sea bed is the limit to the trough depth.

@danielhaish I suspect that y our question is not yet formed completely in your mind. Perhaps you will find that the content of this thread will help you rephrase your question. Is there anything here that's helped you so far?

yes it did helped so you saying that if the normal value without any wave will be the minimum the wave can't go lower thanks I got it

 

[sophiecentaur]

so you saying that if the normal value without any wave will be the minimum the wave can't go lower thanks I got it

I'm not sure what you are actually saying - could be right but you put it in an odd way. Normal waves will change values about a mean position that's the 'rest' position - such as a calm sea or a straight string. Usually, if there's something to stop this sort of motion, the energy will be dissipated over a short distance and the amplitude will drop quickly. (e.g. waves rolling onto the shore and breaking as the beach gets shallower.

 

[Vanadium 50]

You've defined the "normal value" to be the bottom. You can always do that, even with a sine wave.

 

[anorlunda]

Consider a mass and a spring. Initially, the mass is at the zero position. Now you move the mass and let it go. It oscillates around zero, and eventually returns to the zero position.

Now compare that to stretching the spring, but then carrying the whole apparatus up to the second floor before letting it go. Now it oscillates around the second floor elevation which is not the initial zero.

Edit: The second example superimposes a wave solution with a linear height change solution. Superposition is an important concept in physics that you should keep in mind.

 

[danielhaish]

You've defined the "normal value" to be the bottom. You can always do that, even with a sine wave.

not really i define the zero point when there is no wave at all

 

[DaveC426913]

not really i define the zero point when there is no wave at all

Not 'point' ... line.

Vanadium was talking the normal value - the baseline.

 

[danielhaish]

Not 'point' ... line.

Vanadium was talking about baseline.

View attachment 266973

sorry line,any way i mean that for example if you taking about the height of the sea when there is a wave it going lower and then higher so it still lower then the height of the sea when there is no wave at all

 

[DaveC426913]

sorry line,any way i mean that for example if you taking about the height of the sea when there is a wave it going lower and then higher so it still lower then the height of the sea when there is no wave at all

Yes. The point is: that an arbitrary choice, for the convenience of whatever you plan to do.
There are certainly reasons why you might want to set the baseline at the minimum, rather than the median.

A spurious example: an intake pipe, set in a lake, for a water-cooled motor. You don't want it to suck air.

The lake level has an annual rise and fall that approximates a sine wave.

It doesn't matter what the average or median water level is. What matters is the water level at its minimum.

So you set zero to the lowest point on the sine wave. As long as your readings are positive, your intake is under water and cooling properly.

 

[sophiecentaur]

not really i define the zero point when there is no wave at all

What exactly do you mean by "no wave at all" The only place where there is no wave is where the amplitude (or perhaps the average displacement or the Energy) is always zero. A wave is something dynamic - changing all the time in the region where it exists. I am confused as to where this is all going. The Maths of the wave (or perhaps a graph) is just a representation which can be drawn to any scale and with any origin and axes.

Choosing to take a water surface wave as an example is to choose a case that is far from simple. The wave exists by virtue of the movement of the water back and forth and up and down (in circles) at all depths under the surface. Unfortunately for this 'simple' example the waves are not actually sinusoidal either except as an approximation as the amplitude approaches zero. It's for a good reason that the wave that's usually chosen for the simplest analysis is a wave on a string.

You could say, I suppose, that in the air above and below and to the side of a vibrating string (where the string never moves to) is where there is "no wave at all". But there is nothing to be said about those regions that have nothing to do with the wave . . . . so why?? and so what?

 

[some bloke]

for a natural one which would reflect your "untitled 4" graph, with the peaks present but the troughs removed (but the time still present between them), imagine a pendulum, on a long string. The pendulum is raised and swings down. when the string is vertical, it impacts a horizontal bar halfway down the string. The weight continues to swing, on the lower half of the string, and the upper half of the swing stays still until the weight swings back past the bar. If you were to plot the displacement of the mid-point of the string, which impacts the horizontal bar, it would give you the graph you sketched.

 

[sophiecentaur]

If you were to plot the displacement of the mid-point of the string, which impacts the horizontal bar,

Such a wave wouldn't propagate because, once the string was stationary, the energy would be lost. You could use a loudspeaker to produce a wave with approximately that sort of shape but it would involve a very wide band of frequency components (Fourier series) which would add together during the 'flat' portion of the waveform.

 

[anorlunda]

The picture shows the locus of a double pendulum. Where is the zero point in those waves?

 

[sophiecentaur]

It's hard o identify an actual wave, in the normal accepted sense. We are starting off with basics, surely and although there is an oscillation here which varies through space and time and transfers energy (or an abstract equivalent) rather than a simple mass and spring or pendulum in a plane, if we are trying to sort out the OP question, we are only getting further and further away from a solution.
There is no rule afaics for identifying where is the wave and what 'isn't wave'.

 

[madness]

Action potentials in neurons basically do that. If you drive a neuron with a constant current, it will fire action potentials at a regular frequency without dropping below its baseline membrane potential. In reality neurons may be more complicated and may drop slightly below baseline after firing an action potential but to a first approximation, and within the simpler mathematical models, they fit the bill for your question.

 

[sophiecentaur]

Action potentials in neurons basically do that. If you drive a neuron with a constant current, it will fire action potentials at a regular frequency without dropping below its baseline membrane potential. In reality neurons may be more complicated and may drop slightly below baseline after firing an action potential but to a first approximation, and within the simpler mathematical models, they fit the bill for your question.

This is more of an 'active wave' - like a Mexican Wave. Energy is supplied at intervals along the path to maintain a shape. In this way, a wave can be tailored to do anything and we get further and further away from the idea of Waves as an Energy Transport Mechanism, (Your can do what you like in a simulation, for instance.)