This is a source of a Solid State physics demonstration
of wave motion. The balls are on two types of carrier waves, 
one propagates at the opposite direction.
<listing>
k0=Pi/0.30//N

For[t=0,t<12,t=t+0.3, {data = {};
For[x=0,x<5,x=x+0.30, data=Append[data,{x,Sin[ 3 x -t]}]   ];
ListPlot[data,
PlotStyle -> {PointSize[0.05]},DisplayFunction->$DisplayFunction ];   }]

For[t=0,t<12,t=t+0.3, {data = {};
For[x=0,x<5,x=x+0.30, data=Append[data,{x,Sin[3 x -t]}]   ];
Plot0:=ListPlot[data,PlotStyle -> {PointSize[0.05]},DisplayFunction->Identity];
Plot1:=Plot[Sin[3 x -t],{x,0,6},DisplayFunction->Identity];
Show[{Plot0,Plot1}, PlotRange->All,DisplayFunction->$DisplayFunction] }]

For[t=0,t<12,t=t+0.3, {data = {};
For[x=0,x<2.5,x=x+0.30, data=Append[data,{x,Sin[ 3 x -t]}]   ];
Plot0:=ListPlot[data,PlotStyle -> {PointSize[0.05]},DisplayFunction->Identity];
Plot1:=Plot[Sin[(-17.944) x -t],{x,0,2.5},DisplayFunction->Identity];
Show[{Plot0,Plot1}, PlotRange->All,DisplayFunction->$DisplayFunction] }];

For[t=0,t<12,t=t+0.3, {data = {};
For[x=0,x<2.5,x=x+0.30, data=Append[data,{x,Sin[ 3 x -t]}]   ];
Plot0:=ListPlot[data,PlotStyle -> {PointSize[0.05]},DisplayFunction->Identity];
Plot1:=Plot[Sin[(3) x -t],{x,0,2.5},DisplayFunction->Identity];
Show[{Plot0,Plot1}, PlotRange->All,DisplayFunction->$DisplayFunction] }]
</listing>