Which of the following best represents the average speed of a fast runner?

#Which of the following best represents the average speed of a fast runner? full

(a) Calculate EarthвЂ™s average speed relative to the Sun. (Displacement is change in position and, thus, is zero for a round trip.) Thus average speed is not simply the magnitude of average velocity.ДЎ. Your average velocity, however, was zero, because your displacement for the round trip is zero. For example, if you drive to a store and return home in half an hour, and your carвЂ™s odometer shows the total distance traveled was 6 km, then your average speed was 12 km/h. So average speed can be greater than average velocity, which is displacement divided by time. We have noted that distance traveled can be greater than displacement. Average speed is the distance traveled divided by elapsed time. Average speed, however, is very different from average velocity. Your instantaneous speed at that instant would be 40 km/h-the same magnitude but without a direction. Or suppose that at one time during a shopping trip your instantaneous velocity is 40 km/h due north. At that same time his instantaneous speed was 3.0 m/s. For example, suppose the airplane passenger at one instant had an instantaneous velocity of в€’3.0 m/s (the minus meaning toward the rear of the plane). Instantaneous speed is the magnitude of instantaneous velocity. Just as we need to distinguish between instantaneous velocity and average velocity, we also need to distinguish between instantaneous speed and average speed. One major difference is that speed has no direction.

In physics, however, they do not have the same meaning and they are distinct concepts.

In everyday language, most people use the terms вЂњspeedвЂќ and вЂњvelocityвЂќ interchangeably. However, under many circumstances, we can find precise values for instantaneous velocity without calculus. Mathematically, finding instantaneous velocity, v, at a precise instant t can involve taking a limit, a calculus operation beyond the scope of this text. (Police give tickets based on instantaneous velocity, but when calculating how long it will take to get from one place to another on a road trip, you need to use average velocity.) Instantaneous velocity v is the average velocity at a specific instant in time (or over an infinitesimally small time interval). A carвЂ™s speedometer, for example, shows the magnitude (but not the direction) of the instantaneous velocity of the car. Over such an interval, the average velocity becomes the instantaneous velocity or the velocity at a specific instant. When we carry this process to its logical conclusion, we are left with an infinitesimally small interval. The smaller the time intervals considered in a motion, the more detailed the information. To get more details, we must consider smaller segments of the trip over smaller time intervals. For example, we cannot tell from average velocity whether the airplane passenger stops momentarily or backs up before he goes to the back of the plane. The average velocity of an object does not tell us anything about what happens to it between the starting point and ending point, however. The minus sign indicates the average velocity is also toward the rear of the plane. Elapsed time О” t is the difference between the ending time and beginning time, and end at 11:50 A.M., so that the elapsed time would be 50 min. For example, a lecture may start at 11:00 A.M. To find elapsed time, we note the time at the beginning and end of the motion and subtract the two. How does time relate to motion? We are usually interested in elapsed time for a particular motion, such as how long it takes an airplane passenger to get from his seat to the back of the plane. This allows us to not only measure the amount of time, but also to determine a sequence of events. We could then use the pendulum to measure time by counting its swings or, of course, by connecting the pendulum to a clock mechanism that registers time on a dial.

#Which of the following best represents the average speed of a fast runner? full

We might, for example, observe that a certain pendulum makes one full swing every 0.75 s. The SI unit for time is the second, abbreviated s.

The amount of time or change is calibrated by comparison with a standard. It is impossible to know that time has passed unless something changes. In physics, the definition of time is simple- time is change, or the interval over which change occurs. It may be a number on a digital clock, a heartbeat, or the position of the Sun in the sky. Every measurement of time involves measuring a change in some physical quantity. As discussed in Physical Quantities and Units, the most fundamental physical quantities are defined by how they are measured.