Manipulate[Plot[Exp[ - (x-t)^2]+Exp[-(x+t)^2],{x,-20,20}, PlotRange->{0,2}], {t,0,20,1,.1}] Manipulate[Plot[Exp[ - (x-t)^2]-Exp[-(x+t)^2],{x,-20,20}, PlotRange->{-1,1}], {t,0,20,.1}] F[x_]:=If[Abs[x]<1,1-Abs[x],0]; Manipulate[Plot[F[x-t]+F[x+t],{x,-20,20}, PlotRange->{0,2}], {t,0,20,.1}]