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在教学中我们对“用天平称空气质量的演示实验”,做了如下改进:先取一只没有打足气的排球,放在天平左盘,右盘放上砝码,使天平平衡。然后,取下排球,用打气筒把排球充足气后,再放在天平上,此时,由于排球内空气质量增加,天平失去平衡,要使天平恢复平衡,必须在右盘增加砝码,这增加的砝码就等于用打气筒充入球内的空气质量。改进后的实验原理分析: 第一次称量时,设右盘砝码的质量为m_1,排球受力如图1所示,G_球为球的重力,G_空为球内空气的重力,空气对球的浮力为F,托盘对球的支持力为N_1。∴N_1=m_球g+m_空g-F 根据力矩平衡,得m_1=m_球+m_空-p_空V_球(1) 第二次称量时,设砝码的质量为m_2,球充气前后
In our teaching, we demonstrated the following as an example of the demonstration of air quality with a balance: First, take a volley ball that has not played an active part and place it on the left hand side of the balance and put the weight on the right hand to balance the balance. Then, remove the volleyball, the inflatable balloon with sufficient gas, and then placed on the balance, this time, due to increased air quality within the volleyball, balance out of balance, to balance the balance, you must add weight in the right disk, which The added weight equals the air mass inflated by the pump. Improved experimental principle analysis: the first weighing, the quality of right-hand weights set m_1, volleyball force shown in Figure 1, G_ ball for the ball’s gravity, G_ empty for the ball of air gravity , The buoyancy of air to the ball is F, and the supporting force of the tray to the ball is N_1. ∴N_1 = m_ball g + m_ empty gF According to the moment balance, we can get m_1 = m_ball + m_value -p_value V_ball (1) At the second weighing, the mass of the weight is m_2 Before and after the ball inflated