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确定起跑线,人教版六年级数学上册第四单元,复习回顾:,100米决赛运动员起跑情形,400米决赛运动员起跑情形,为什么运动员站在不同的起跑线?,确定起跑线,1,3,2,终点线,85.96m,72.6m,1.25m,1.25m,1.25m,1、跑道由( )和( )组成。 2、左右两个半圆形的弯道合起来是( ) 3、现在每一圈跑道的长度可以看成 ( )。,两条直段跑道,一个圆,两个直道的长度加上一个圆的周长,两个半圆形跑道,小组合作:,观察每一条跑道的长度相等吗? 怎样找出相邻两个跑道的差距?,85.96m,72.6m,1.25m,1.25m,1.25m,注:取3.14159,85.96m,72.6m,第一道,直径:,周长:,全长:,72.6m,72.63.14159228.08(m),85.962228.08=400(m),72.6,228.08,400,注:取3.14159,85.96m,72.6m,第一道,直径:,周长:,全长:,72.6m,228.08m,400m,第二道,直径:,周长:,全长:,72.61.251.25=75.1(m),75.13.14159235.93(m),85.962235.93=407.85(m),1.25m,1.25m,72.6,228.08,400,75.1,235.93,407.85,注:取3.14159,85.96m,72.6m,第二道,直径:,周长:,全长:,75.1m,235.93m,407.85m,第三道,直径:,周长:,全长:,75.11.251.25=77.6(m),77.63.14159243.79(m),85.962243.79=415.71(m),1.25m,1.25m,75.1m,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,注:取3.14159,85.96m,72.6m,第三道,直径:,周长:,全长:,77.6m,243.79m,415.71m,第四道,直径:,周长:,全长:,77.61.251.25=80.1(m),80.13.14159251.64(m),85.962251.64=423.56(m),1.25m,1.25m,77.6m,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,注:取3.14159,85.96m,72.6m,第四道,直径:,周长:,全长:,80.1m,251.64m,423.56m,第五道,直径:,周长:,全长:,80.11.251.25=82.6(m),82.63.14159259.50(m),85.962259.5=431.42(m),72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,注:取3.14159,85.96m,72.6m,第五道,直径:,周长:,全长:,82.6m,259.5m,431.42m,第六道,直径:,周长:,全长:,82.61.251.25=85.1(m),85.13.14159267.35(m),85.962267.35=439.27(m),72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,注:取3.14159,85.96m,72.6m,第六道,直径:,周长:,全长:,85.1m,267.35m,439.27m,第七道,直径:,周长:,全长:,85.11.251.25=87.6(m),87.63.14159275.20(m),85.962275.2=447.12(m),72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,注:取3.14159,85.96m,72.6m,第七道,直径:,周长:,全长:,87.6m,275.2m,447.12m,第八道,直径:,周长:,全长:,87.61.251.25=90.1(m),90.13.14159283.06(m),85.962283.06=454.98(m),72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,90.1,283.06,454.98,注:取3.14159,各跑道的起跑线应该相差多少米?,7.85m,/ 7.86m,7.85,7.86,7.85,7.86,7.85,7.85,7.86,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,90.1,283.06,454.98,注:取3.14159,我不用算出每条跑道的长度,也知道它们相差多少米?,两条直道是一样的,所以只需要看圆的周长。圆的周长是这样算的:,第一道:72.6,第二道:(72.62.5) = 72.62.5,第三道:(75.12.5) = 75.12.5,第四道:(77.62.5) = 77.62.5,第五道:(80.12.5) = 80.12.5,第六道:(82.62.5) = 82.62.5,第七道:(85.12.5) = 85.12.5,第八道:(87.62.5) = 87.62.5,每一条跑道都在上一条跑道的基础上增加2.5的长度。你能算出2.5是多少米吗?,终点,起点,200米的跑道,每条道的长度都是它们全长的一半。,第一条:4002=200(m),第二条:407.852=203.925(m),第三条:415.712=207.855(m),第四条:423.562=211.78(m),第五条:431.422=215.71(m),每条道相差3.925m或3,39m。所以起跑线应依次提前约3.925m。,思考:200米跑步比赛,跑道宽为1.25米,起跑线应依次提前多少米?,巩固练习、实践应用:,1、400米的跑步比赛,跑道宽为1.5米,起跑线 该依次提前多少米?如果跑道宽是1.1米呢? 2、在运动场上还有200米的比赛,跑道宽为1.25米,起跑线又该依次提前多少米?,1.523.149.42(m),1.123.146.908(m),1.2523.14 21.253.143.925(m),确定起跑线,每一条跑道的长度两个直道的长度圆的周长 (72.61.252)72.6 (75.11.252)75.1 72.672.61.252 75.175.11.252 1.252 1.252 400米跑相邻跑道相差:跑道宽2,小狗和小兔分别从A、B处出发,沿半圆走到C、D。他们两人走过的路程一样长吗? (1)小狗所走的路线的半径为10米,它走过的路程是 米。 (2)小兔所走的路线的半径为 米,它走过的路程是 米。 (3)两只小动物走过 的路程相差 米。,A,B,D,C,10m,1m,小狗走过的路程:,3.142102=31.4(米),A,B,D,C,10m,1m,小兔走过的路程:,3.142(10+1)2=34.54(米),A,B,D,C,10m,1m,两只动物所走路程相差:,34.54-31.4=3.14(米),谢谢同学们 的坚持!,
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