英语翻译

英语翻译
(30)In everyday life,we use the terms speed and velocity interchangeably可互换,but in physics there is an important distinction between them.Speed depends on the distance traveled,and velocity on the displacement.Speed is the distance traveled by a particle in unit time.If a particle travels identical distances during equal time intervals,its motion is called uniform.In this case,the speed of the particle at each moment can be calculated by dividing the distance by the time .
(31)Forces of friction are typical non-conservative ones.Since the force of friction and the velocity of a particle are directed oppositely,then the work of the force of friction on each part of the path is negative:Therefore,the work along any closed path will also be negative.Hence it follows that the forces of friction are not conservative.
(32)The object of the molecular-kinetic theory is to interpret解释 the properties of bodies that are directly observed in experiments (pressure,temperature,ect) as the summary result of the action of molecules.It uses the statistical method and is interested not in the motion of separated molecules,but only in average quantities characterizing the motion of an enormous combination of particles.This explains its other name-statistical physics.
(33)The internal energy is a function of state of a system.This signifies that whenever a system is in a given state,its internal energy takes on the value characterizing this state regardless of the previous history of the system.Hence,the change in the internal energy when a system passes from one state to another will always equal the difference between the values of the internal energy in these states regardless of the path followed by the transition.In other words,the change in the internal energy does not depend on the process or processes that caused the system to pass from one state to another.