2021年初二物理机械效率知识点.pdf

1/3 澳斯特教育教材系列第5 讲机械效率时间：2017年08 月15 日学生：一、兴趣导入（Topic-in）二、学前测试(Testing)三、知识讲解(Teaching)1.有用功、额外功和总功定义：有用功为了达到某一目的而必须做的功叫有用功，用有用W表示；额外功并非我们需要但又不得不做的功叫额外功，用额外W表示；总功有用功加上额外功是总共做的功，叫做总功。额外有用总WWW例 1：下列有关有用功和额外功的说法，正确的是（）A、用水桶从井中提水时，对水做的功是有用功，而对水桶做的功是额外功B、用水桶从井中提水时，对水桶做的功是有用功，对水做的功是额外功C、当水桶掉到井里，需要将水桶打捞上来时，对水桶做的功是有用功，而对桶内的水做的功是额外功D、从水井中打捞水桶时，对水做的功是有用功，对水桶做的功是额外功2.机械效率定义：有用功跟总功的比值叫做机械效率，用表示。%100总有用WW例 2：要提高滑轮组的机械效率，下列做法中正确的是（）A、使用轻质滑轮B、用滑轮组提升很轻的物体C、在滑轮的轮和轴之间注些润滑油D、以上都可以四、训练辅导(Tutor)1.小玲同学值日时用水桶提水从一楼到三楼，她做的有用功是（）|精.|品.|可.|编.|辑.|学.|习.|资.|料.*|*|*|*|欢.|迎.|下.|载.第 1 页，共 3 页2/3 A、对桶所做的功B、对水做的功C、对水和桶做的功D、对水、桶和人做的功2.下列关于提高机械效率的说法中，正确的是（）A、越省力的机械，机械效率越高B、做的有用功越多，机械效率越高C、做的总功越少，机械效率越高D、额外功在总功中占的比例越小，机械效率越高3.用一动滑轮把重96 N 的物体 A 提升 2 m，所用拉力为60 N，则拉力所做的有用功和动滑轮的机械效率分别是（）A、192 J，20%B、120 J，20%C、192 J，80%D、120 J，80%五、强化练习(Training)1.体重是 400 N 的同学用重10 N 的水桶，提起重为100 N 的水沿楼梯送到5 m 高的宿舍里使用。则完成这一次提水，做的有用功和额外功分别是（）A、500 J 50 J B、500 J 2050 J C、550 J 2000 J D、2500 J 50 J 2.小明的妈妈在楼下的超市买了一袋质量为25 kg 的大米，超市员工帮她扛上楼，在上楼过程中，对超市员工来说，有用W=J，额外W=J，总W=J。（g取 10 N/kg，员工体重为60 kg，登楼高度为18 m）3.关于机械的功、功率和机械效率，以下说法正确的是（）A、利用机械越省力，机械效率越高B、机械做功越快，机械效率越高C、机械的功率越大，做功越多D、机械的功率越小，做功越慢|精.|品.|可.|编.|辑.|学.|习.|资.|料.*|*|*|*|欢.|迎.|下.|载.第 2 页，共 3 页文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F1文档编码:CZ4J3G1J8F4 HA10K4R3U3U1 ZE2I1R5R3F13/3 六、反思总结(Thinking附件：堂堂清-测试题学生：关于功率和机械效率，下列说法正确的是（）A、功率大的机械，机械效率一定高B、做功多的机械，机械效率一定高C、机器的功率越大，做功就越多D、机器的功率越大，做功就越快|精.|品.|可.|编.|辑.|学.|习.|资.|料.*|*|*|*|欢.|迎.|下.|载.第 3 页，共 3 页文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 ZE5Y2M6N3S3文档编码:CM3F2P7W6C1 HS10A3C1B7P6 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