holder 39 the forces may be adjusted by adjusting the nuts 45 and also by removing the coil springs 43 and substituting other coil springs with different spring constants the spring constant of the springs 43 are set precisely for studies such as system dynamics friction and vibration and stick slip phenomenon in the present embodiment a horizontal insulating member 47 is positioned on the base 16 a pair of spaced insulating side walls 48 extend upwardly from the insulating member 47 the insulating member 47 and the insulating side walls 48 receive a holder 49 having a central slot 50 for receiving a band heater 51 a plurality of screws 53 interconnect the base 16 the insulating member 47 the holder 49 and the lower sample holder 39 preferably the insulating member 47 and the insulating side walls 48 are constructed of ceramic materials in order to reduce heat transfer the ball bearings 32 when in contact with the bearing edges 35 of the upper specimen holder 34 guide the specimen holder 34 during its reciprocating motion therefore the load is transferred from the coil springs 43 to the upper plate 23 and downwardly to the upper sample holder 34 through the ball bearings 32 referring to fig6 the sliding unit 11 is.