2 added 6 characters in body
source | link
Show[newplot /.  LineLegend[a_, b___]b_, c___] :> 
   LineLegend[a, b, LabelStyle -> {FontFamily -> "Times", FontSize -> 12}], c], 
 ImageSize -> 8 72, AspectRatio -> 1/4, 
 FrameLabel -> {"Time / s", "Force / N"}, 
 LabelStyle -> {FontFamily -> "Times", FontSize -> 12}, 
 FrameTicksStyle -> Thick]

enter image description here

Show[newplot /.  LineLegend[a_, b___] :> 
   LineLegend[a, b, LabelStyle -> {FontFamily -> "Times", FontSize -> 12}], 
 ImageSize -> 8 72, AspectRatio -> 1/4, 
 FrameLabel -> {"Time / s", "Force / N"}, 
 LabelStyle -> {FontFamily -> "Times", FontSize -> 12}, 
 FrameTicksStyle -> Thick]

enter image description here

Show[newplot /.  LineLegend[a_, b_, c___] :> 
   LineLegend[a, b, LabelStyle -> {FontFamily -> "Times", FontSize -> 12}, c], 
 ImageSize -> 8 72, AspectRatio -> 1/4, 
 FrameLabel -> {"Time / s", "Force / N"}, 
 LabelStyle -> {FontFamily -> "Times", FontSize -> 12}, 
 FrameTicksStyle -> Thick]

enter image description here

1
source | link

Show[newplot /.  LineLegend[a_, b___] :> 
   LineLegend[a, b, LabelStyle -> {FontFamily -> "Times", FontSize -> 12}], 
 ImageSize -> 8 72, AspectRatio -> 1/4, 
 FrameLabel -> {"Time / s", "Force / N"}, 
 LabelStyle -> {FontFamily -> "Times", FontSize -> 12}, 
 FrameTicksStyle -> Thick]

enter image description here