# What actually is a wave? [duplicate]

Can someone please explain what actually is a wave?I have read it is disturbance which transfers energy but am unable to get a intuitive feel of it. For example I cannot understand if it is a disturbance why we represent wave by the customary curve resembling sine graph. What does the curve actually represents?

• In the general case, the sine curve represents the phase of the wave. It can also be represented by color, for example.
– user137289
Nov 1, 2019 at 20:18
• A wave doesn't have to be represented by a sine curve. A sine-shaped wave form is common, but a square-form or any other form is also called a wave. Nov 1, 2019 at 20:22
• But it represents what? phase of what? Nov 1, 2019 at 20:23
• Possible duplicate of What is a wave? Nov 2, 2019 at 18:54
• e.g. a wave as a function of time can be described as f(x-vt). it translates to the right with a velocity v. Nov 3, 2019 at 3:08

Think of a rope tied to the wall in one end. Flick it fast up and down.

• On its way up, you have set the very first "particle" of this rope in upwards motion.
• Its neightbour "particle" is directly tied to it, so this neighbour follows along upwards. But their connection - their "bond" - might be slightly flexible. So, this neighbour "particle" moves upwards with a short delay.
• Repeat this for every single "particle" one after the other.

Essentially, the kinetic energy you applied to the first "particle" is transferred to its neighbour, and then to the neighbour's neighbour etc. Soon, the energy is transferred by the very last "particle" to the hook in the wall. If that hook is a switch, or something like that, you can flick the rope and turn the light on and off. This progression of energy in a material or similar that is slightly flexible is a wave. And the shape could be anything.

A key point here is that each "particle" in this mechanical rope is not moving sideways, only upwards. This is a transverse wave. The energy moves horizontally, but not the "particles" themselves. This is also the case in water waves; a rubber duck will ideally never move sideways but only up and down with the wave. If you clap your hands, then the air particles are accelerated next to your skin. They bump into their neighbours with a similar delay, and those neighbours bump into their neighbours etc. We now have wave particles moving/vibrating horizontally while energy is also transferred horizontally. We call this a longitudinal wave.

A wave on a rope clearly and visibly shows the shape it has. Something similar to the sine-curve you describe. It will be exactly equal to a sine curve, if your rope-flicking is constant (not varying in speed during an up-and-down flick) and if there is no energy loss along the way. There is very often energy loss, though, and then you have a damped wave, with smaller and smaller amplitudes.

Whenever this now well-recognisable wave-shape is seen in other circumstances, we also call it a wave. The sound-wave mentions do not mechanically look like this, but draw up the air particle locations on a y-axis and time on the x-axis, and you have a similar wave-form.

We also call AC voltage a wave, because its signal (if you draw out the varying voltage over time on a graph) has the wave form; we call electric and magnetic rays waves, because they interact exactly as mechanical waves do, when they meet other waves (constructive and destructive interference) etc. In each of these more abstract cases, the wave motion is always energy - and the medium (if there is one) depends on the situation and the phenomenon.

I like to think of a wave as a thing or the sum of many similar things that have a property that is measurable and is changing spatially / temporally on a periodic basis about an equilibrium point.