Chapter 16 Kinetic Theory of Gases 单个分子遵循力学规律 1.跟踪第分子,它在某一时刻的速度乙在x方向的分 量为 则有 ∑ IX 2、x方向动量变化4P=-m01x-myx=-2mx The change in momentum, which is the final momentum minus the initial momentum
Chapter 16 Kinetic Theory of Gases 则有 单个分子遵循力学规律 The change in momentum, which is the final momentum minus the initial momentum. 2、x方向动量变化 pi x = −mvi x − mvi x = −2mvi x 1.跟踪第i个分子，它在某一时刻的速度 在x方向的分 量为 . i v ix v = = i x i x N 2 2 1 2 3 1 v v v
Chapter 16 Kinetic Theory of Gases 3、分子与A2面发生碰撞后,又与A1面发生碰撞,相继 两次对A1面碰撞所用的时间: The time it takes the molecule to travel across the box and back again, a distance equal to 2x. △t=2x/Ux 4器壁A所受冲力 The average force will be equal to the force exerted during one collision divided by the time between collisions: F △(m0)2m v-m/x △t2x/U
Chapter 16 Kinetic Theory of Gases 3、分子与A2面发生碰撞后，又与A1面发生碰撞，相继 两次对A1面碰撞所用的时间： The time it takes the molecule to travel across the box and back again, a distance equal to 2x. ix t = 2x v 4 器壁 所受冲力 The average force will be equal to the force exerted during one collision divided by the time between collisions: m x x m t m F x x x 2 2 2 v v v v = = = / ( ) A1
Chapter 16 Kinetic Theory of Gases 大量分子总效应 单位时间N个粒子对器壁 To calculate the force due to all the molecules in the box we have to add the contribution of each. The net force on the wall ∑ 10 ∑ Ni IX 器壁4所受平均冲力F=72MWm/x 统计规律=N x2x 2 Xyz 3
Chapter 16 Kinetic Theory of Gases 大量分子总效应 单位时间 N 个粒子对器壁 To calculate the force due to all the molecules in the box, we have to add the contribution of each. The net force on the wall 2 2 2 2 x i x i i x i i x x Nm x N Nm x m x m F v v v v i = = = = 器壁 所受平均冲力 F Nm x x 2 A1 = v 统计规律 xyz N n = 2 2 3 1 vx = v
Chapter 16 Kinetic Theory of Gases p386 X pressure p yz xyz 37 分子平均平动动能 average kinetic energy K m0p=11÷m02=n××m02==HK 3 3 p=nk
Chapter 16 Kinetic Theory of Gases pressure 2 2 3 3 v v V Nm xyz Nm yz F p = = = 分子平均平动动能 average kinetic energy 2 2 1 K = mv p nK 3 2 = p n m n m nK 3 2 2 1 3 2 3 1 2 2 = v = v = 3 2 v N x m F = p386
Chapter 16 Kinetic Theory of Gases 压强的物理意义 统计关系式 P 3 K 宏观可测量量微观量的统计平均值 ◆压强是大量分子对时间、对面积的统计平均结果 表明压强具有统计意义,即它对于大量气体分子才有明确 的意义。 P∝n分子数密度越大,压强越大; P∝K分子运动得越激烈,压强越大
Chapter 16 Kinetic Theory of Gases p nK 3 2 = 统计关系式 宏观可测量量 微观量的统计平均值 压强是大量分子对时间、对面积的统计平均结果 . 表明压强具有统计意义，即它对于大量气体分子才有明确 的意义。 P n 分子数密度越大，压强越大； P K 分子运动得越激烈，压强越大。 压强的物理意义