Clear[]
l = 100
n = 3
u[x_, t_] := 
      5  Sin[(((2 n - 1) π)/(2 l)) x]*
        Cos[(((2 n - 1) π)/(2 l)) 
            t]

    
m1[t_] := 
      Show[Graphics[{RGBColor[0, 0, 0], Line[{{0, -3}, {0, 3}}]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m2[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[10, t] + 10, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m3[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[20, t] + 20, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m4[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[30, t] + 30, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m5[t_] := 
      Show[Graphics[{RGBColor[1, 0, 0], Disk[{u[40, t] + 40, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m6[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[50, t] + 50, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m7[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[60, t] + 60, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m8[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[70, t] + 70, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m9[t_] := 
      Show[Graphics[{RGBColor[1, 0, 0], Disk[{u[80, t] + 80, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m10[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[90, t] + 90, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]
m11[t_] := 
      Show[Graphics[{RGBColor[0, 1, 0], Disk[{u[100, t] + 100, 0}, 1]}, 
          AspectRatio -> Automatic], 
        DisplayFunction -> Identity]

    
g = 
      Table[Show[m1[t], m2[t], m3[t], m4[t], m5[t], m6[t], m7[t], m8[t], 
          m9[t], m10[t], m11[t], 
          PlotRange -> {{-2, 130}, {-3, 3}}, 
          DisplayFunction -> $DisplayFunction], {t, 0, 1000, 
          5}]
Export["movie_rod_n_3.avi", g]