![]() ![]() 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. 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- timeis 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. TimeĪs discussed in Chapter 1.2 Physical Quantities and Units, the most fundamental physical quantities are defined by how they are measured. ![]() In this section we add definitions of time, velocity, and speed to expand our description of motion. Questions such as, “How long does a foot race take?” and “What was the runner’s speed?” cannot be answered without an understanding of other concepts. There is more to motion than distance and displacement. The motion of these racing snails can be described by their speeds and their velocities. 2 Kinematics 9 2.3 Time, Velocity, and SpeedĮxplain the relationship between instantaneous velocity, average velocity, instantaneous speed, average speed, displacement, and time.Ĭalculate velocity and speed given initial position, initial position, final position, and final time.ĭerive a graph of velocity vs. ![]()
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