Originally posted by Wickedcummins
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So what your tell me is a wave is a periodic disturbance in space and/or time. By periodic we mean that its manifestation is seen several times (in time and/or space). Waves transfer energy (information) through a medium without displacing much the medium itself?
The speed of a group of waves is called the group-speed (cg) of the wave and is the speed by which energy propagates. The two are not necessarily the same. For example, in a boat's wake one can observe how crests rise from the rear end of the edge formed behind the boat and disappear in its front edge, moving faster (in fact twice as fast) as the propagation of the wedge itself (the 'group').
Deep water waves of different length travel at different speeds (the long ones faster than the short ones), all shallow water waves travel at the same speed.
An object moving along on the fluid surface (boat, duck), generates a surface wave with two crests at both ends of the object and the trough in between. The length is approximately equal to the water-line length of the hull (L). The natural phase speed of this wave is c=(gL/(2p))1/2, and is called the hull speed. If the objects tries to swim faster than its hull speed it will need to move uphill over the wave it is forming, creating extra resistance in the process. The energetic cost of moving faster than the hull speed is such that ducks do not attempt it and so do not boats. Thus the length of a boat (swimmer) is very important in determining the maximal speed that can be sustained for a while.
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(Ocean) When deep water waves get to shallow areas their speed decrease and their amplitudes increase accordingly (to conserve mass). Once the wave achieve critical steepness (H/l~1/7) they break (Fig. 6). The energy the wave had is mostly dissipated into heat. Some of the energy may be channeled into creating strong 'rip' currents.
The way the hulls shape or angle compresses and releases the waters mass and at the speed it is doing that is what creates the break or curl.
The speed of a group of waves is called the group-speed (cg) of the wave and is the speed by which energy propagates. The two are not necessarily the same. For example, in a boat's wake one can observe how crests rise from the rear end of the edge formed behind the boat and disappear in its front edge, moving faster (in fact twice as fast) as the propagation of the wedge itself (the 'group').
Deep water waves of different length travel at different speeds (the long ones faster than the short ones), all shallow water waves travel at the same speed.
An object moving along on the fluid surface (boat, duck), generates a surface wave with two crests at both ends of the object and the trough in between. The length is approximately equal to the water-line length of the hull (L). The natural phase speed of this wave is c=(gL/(2p))1/2, and is called the hull speed. If the objects tries to swim faster than its hull speed it will need to move uphill over the wave it is forming, creating extra resistance in the process. The energetic cost of moving faster than the hull speed is such that ducks do not attempt it and so do not boats. Thus the length of a boat (swimmer) is very important in determining the maximal speed that can be sustained for a while.
.................................................. .....................
(Ocean) When deep water waves get to shallow areas their speed decrease and their amplitudes increase accordingly (to conserve mass). Once the wave achieve critical steepness (H/l~1/7) they break (Fig. 6). The energy the wave had is mostly dissipated into heat. Some of the energy may be channeled into creating strong 'rip' currents.
The way the hulls shape or angle compresses and releases the waters mass and at the speed it is doing that is what creates the break or curl.
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