One Dimensional Motion
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One dimensional motion is motion along a straight line.
The line used for this motion is often the familiar x-axis, or x number line. The object may move forward or backward along this line.
Forward is usually considered positive movement and this movement is usually considered to the right. So, as an object moves forward down the x-axis, it is heading toward larger and larger x coordinates, and we say that it has a positive displacement and a positive velocity.
Backward is usually considered negative movement to the left. As an object moves backward along the x-axis, it is heading toward smaller and smaller x coordinates, and we say that it has a negative displacement and a negative velocity.
Here is a VRML world showing an object moving along with a constant positive velocity:
In the above animation we say that the displacement is positive because the changes in position over which the object moves are toward larger and larger coordinate positions. That is, for any segment of the motion the later x coordinate, i.e., x2, is greater than the former x coordinate, i.e., x1. This makes the displacement, i.e., (x2 - x1), a positive value.
In the above animation we say that the velocity is positive, ultimately, because the displacement is positive, and velocity follows the direction of the displacement. Another way to think about it is that conventionally movement to the right is considered to be a positive velocity.
Also, in the above animation notice that the object moves through equal distances during equal time intervals. This is what we mean by a constant velocity.
Here is a VRML world showing an object moving along with a constant positive acceleration:
In the above animation we notice that the object moves faster and faster as it goes from left to right. This speeding up is one type of acceleration. Notice that the object covers more distance in the later time intervals than in the early ones. This is because in the later time intervals it is traveling faster.
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