Silver Burdett/

Science: Understanding Your Environment/

Transportation on Land and Water p. 85/

1975/

/

/

S4N8/

*****

/-/The wheel is*N1 one (of the greatest inventions )(of history. )/-/(Without the wheel, )travel was*A1 difficult. /-/(Before wheels, )most people walked*- or rode*D1 horses. /-/People or horses had to drag*D1 objects (from one place )(to another. )/-/Wheels made*D1I it=IEL081 easier to do=IDS061 some kinds (of work. )/-/Work is done*P [ARwhenever a force moves*D1 something. ]/-/It takes*D1 effort to do=IDS031 work. /-/It takes*D1 effort (for you )to walk.=IDS020 /-/You use*D1 effort [ARwhen you lift*D1 something. ]/-/Effort is needed*P to stretch=IAV041 a spring. /-/The more you stretch*D1 a spring, [ARthe more effort it takes.*D1 ]/-/Spring scales can be used*P to measure=IAV031 effort. /-/Suppose*D1 [DOyou must move*D1 a 100-pound object. ]/-/You can slide*D1 the object. /c/Or you can move*D1 the object (in a wagon )(with wheels. )/-/Suppose*D1 [DOthe wagon weighs*N1 20 pounds. ]/-/You have to move*D1 more weight [ARwhen the object is*-1P (in the wagon. )]/-/Look again at*D1 the picture (of the Indian travois )truhVOY=APR01 (on page 84. )/-/The weight (of the object )is carried*P (on the poles. )/-/Some (of the weight )rests*- (on the horse. )/-/Some (of the weight )is*-1P (on the poles )[ARwhere they touch*D1 the ground. ]/-/You can see*D1 marks (on the ground )(behind the poles. )/-/The poles moved*D1 some soil [ARas they slid.*- ]/-/Some (of the effort )(of the horse )was used*P to move=IAV041 this soil. /-/Was*N1 this wasted=P--01 effort? /-/Wheels carry*D1 the weight (of a load )(on a wagon. )/-/Wheels may also leave*D1 marks [ARwhere they travel.*- ]/-/Most wheels [JMthat carry*D1 loads ]do not move*D1 much (of the soil )[JR(over which )they travel.*- ]!!!!!!!!