Parameters Involving Length and Time

In this section, we vinli contider derived physical quantities that are based on die fundamental dimensions of length and time. We will first discuss the concepts of linear speed and acceleration and then define volumetric flow rate. 

Let us now take a dose look at what we mean by linear speed and linear vdodty. All of you are familiar with a car speedometer. It shows the instantaneous speed of a car. Before we ocplain in more detail vdiat we mean by the term instantaneous speed, let us define a physical variable that is mote easily understood, the averagesp d, which is defined as 

To better understand the difference between the aver speed and the instantaneous speed, ask yourself the following question. If you needed to locate the car, would you be able to locate the car knowing just the average speed of the cai The knowlet of the average speed of the car would not be sufficient. To know where the car is at all times, you need more information, such as the instantaneous speed of the car and the direction in which it is traveling. This means you must know the instantaneous velodly of the car. Note that when we say velocity of a car, we not only refer to the speed of the car but also the direction in which it moves. 

Physical quantities that possess both a magnitude and a direction are called vectors, fou will learn more about vectors in your calculus, physics, and mechanics classes. For now, just remember the simple definition of a vector quantity—a quantity that has both m nitude and direcdon. A physical quantity that is described only by a magnitude is called a scalar quantity. Examples of scalar quantifies include temperature, volume, and mass. Examples of the range of speed of various objects are given in Table 8.2. 

Again note that acceleration uses only the dimensions of length and time. Acceleration represents the rate at which the velocity of a moving object changes wdth time. Therefore, acceleration is the time rate of change of velocity. The SI unit for acceleration is m/s and in U.S. Customary units ft/s.  

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