(2)TheKinetic-MolecularTheorySupposing that there are N gas molecules whose weightis m in a cube Im on an edge, 1/3 move up and down1/3 move back and forth, and 1/3 move right and left今考虑一个分子，速度为u左右运动，该分子每撞壁一次动量改变的绝对值为2muj,△t=21 / u单位时间内动量的变化就是力F=2mu, / △t=mu2/
16 （2） The Kinetic-Molecular Theory Supposing that there are N gas molecules whose weight is m in a cube l m on an edge，1/3 move up and down, 1/3 move back and forth, and 1/3 move right and left. 今考虑一个分子，速度为 u1左右运动,该分子每撞壁 一次动量改变的绝对值为 2mu1 , △t = 2l / u1 单位时间内动量的变化就是力 F = 2mu1 / △t = mu1 2 / l
F=ZFi ="(Nu?+ N,u? +..)iNu? + N,u? +..mN31YNmN31Ni + N2 + N3 + ... = N /3速度平方的均数Nu' + N,u? +..uYN
17 N1 + N2 + N3 + . = N /3 速度平方的均数 2 2 2 2 2 1 1 2 2 2 2 1 1 3 3 3 1 u l mN N N u N u l mN N u N u l m F Fi i = + + = = = + + ( ) N N u N u u 3 1 2 2 2 2 2 1 1 + + =