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Answer:
a space-probe flyby of the planet Neptune involves motion. When you
are resting, your heart moves blood through your veins. And even in inanimate objects, there is continuous motion in the vibrations of atoms and
molecules. Questions about motion are interesting in and of themselves: How long will it take for a space probe to get to Mars? Where will a football
land if it is thrown at a certain angle? But an understanding of motion is also key to understanding other concepts in physics. An understanding of
acceleration, for example, is crucial to the study of force.
Our formal study of physics begins with kinematics which is defined as the study of motion without considering its causes. The word “kinematics”
comes from a Greek term meaning motion and is related to other English words such as “cinema” (movies) and “kinesiology” (the study of human
motion). In one-dimensional kinematics and Two-Dimensional Kinematics we will study only the motion of a football, for example, without worrying
about what forces cause or change its motion. Such considerations come in other chapters. In this chapter, we examine the simplest type of
motion—namely, motion along a straight line, or one-dimensional motion. In Two-Dimensional Kinematics, we apply concepts developed here to
study motion along curved paths (two- and three-dimensional motion); for example,must first be able to describe its position—where it is at any particular time. More precisely, you
need to specify its position relative to a convenient reference frame. Earth is often used as a reference frame, and we often describe the position of
an object as it relates to stationary objects in that reference frame. For example, a rocket launch would be described in terms of the position of the
rocket with respect to the Earth as a whole, while a professor’s position could be described in terms of where she is in relation to the nearby white
board. (See Figure 2.3.) In other cases, we use reference frames that are not stationary but are in motion relative to the Earth. To describe the
position of a person in an airplane, for example, we use the airplane, not the Earth, as the reference frame. (See Figure 2.4.)
Displacement
If an object moves relative to a reference frame (for example, if a professor moves to the right relative to a white board or a passenger moves toward
the rear of an airplane), then the object’s position changes. This change in position is known as displacement. The word “displacement” implies that
an object has moved, or has been displaced.
Displacement
Displacement is the change in position of an object:
Δx = x (2.1) f − x0
,
where Δx is displacement, xf
is the final position, and x0
is the initial position.
In this text the upper case Greek letter Δ (delta) always means “change in” whatever quantity follows it; thus, Δx means change in position.
Always solve for displacement by subtracting initial position x0
from final position xf
.
Note that the SI unit for displacement is the meter (m) (see Physical Quantities and Units), but sometimes kilometers, miles, feet, and other units of
length are used. Keep in mind that when units other than the meter areassenger moves from his seat to the back of the plane. His location relative to the airplane is given by x . The −4.0-m displacement of the passenger
relative to the plane is represented by an arrow toward the rear of the plane. Notice that the arrow representing his displacement is twice as long as the arrow representing the
displacement of the professor (he moves twice as far) in Figure 2.3.
Note that displacement has a direction as well as a magnitude. The professor’s displacement is 2.0 m to the right, and the airline passenger’s
displacement is 4.0 m toward the rear. In one-dimensional motion, direction can be specified with a plus or minus sign. When you begin a problem,
you should select which direction is positive (usually that will be to the right or up, but you are free to select positive as being any direction). The
professor’s initial position is x0 = 1.5 m and her final position is xf = 3.5 m . Thus her displacement is
Δx = x (2.2) f −x0 = 3.5 m − 1.5 m = + 2.0 m.
In this coordinate system, motion to the right is positive, whereas motion to the left is negative. Similarly, the airplane passenger’s initial position is
x0 = 6.0 m and his final position is xf = 2.0 m , so his displacement is
Δx = x (2.3) f −x0 = 2.0 m − 6.0 m = −4.0 m.
His displacement is negative because his motion is toward the rear of the plane, or in the negative x direction in our coordinate system.
Distance
Although displacement is described in terms of direction, distance is not. Distance is defined to be the magnitude or size of displacement between
two positions. Note that the distance between two positions is not the same as the distance traveled between them. Distance traveled is the total
length of the path traveled between two positions. Distance has no direction and, thus, no signal
Explanation: pls brainlist
