题目　给你一只量筒 ,一只烧杯 ,一根足够长的细线 ,一个水槽及足量的水 ,请利用上述全部器材测出新鲜土豆的密度 (土豆的样品已取好 ,大小合适 ,其密度比水大 ,且不再吸水 ) .( 1 )写出主要的实验步骤及测量的物理量符号 .( 2 )写出土豆密度的表达式 ρ土豆 =　　 .分析　此题 The subject gives you a measuring cylinder, a beaker, a long enough thread, a sink, and a sufficient amount of water. Use all the above equipment to measure the density of the fresh potatoes. (The samples of potatoes have been taken and the size is appropriate. Density is greater than water, and no longer absorbs water.) (1) Write the main experimental procedure and the measured physical quantity symbol. (2) Write the expression of potato density ρ potatoes = . Analysis of this question