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CHAPTER 2. Kinematics in One Dimension. Pgs. 19-37. MECHANICS: the study of the motion of objects & related forces. Two divisions of mechanics:. Kinematics : describe HOW objects move Dynamics : deals with forces & WHY objects move. Translational Motion.
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CHAPTER 2 Kinematics in One Dimension Pgs. 19-37
MECHANICS: the study of the motion of objects & related forces. Two divisions of mechanics: • Kinematics: describe HOW objects move • Dynamics: deals with forces & WHY objects move
Translational Motion • In chapter 2, we will only discuss objects that move without rotating. • This type of motion is called: TRANSLATIONAL MOTION
REFERENCE FRAME • Any measurement of position, distance, or speed must be made with respect to a frame ofreference.
Reference frame or Frame of Reference • A person walks 5 km/h. The train is moving at 80 km/h with respect to the ground. How fast is the person going with respect to the ground?
Specifying the Motion of an Object • We often specify the motion of an object by using a set of coordinate axes. This can represent our frame of reference. • For one dimensional motion, we choose the x-axis as the line along which motion takes place. • If an object is dropped, motion is vertical and we use the y-axis.
DISTANCE vs. DISPLACEMENT • Distance traveled here is not the same as the DISPLACEMENT! • Displacement is the change in postion of the object or how far the object is from its starting position. Total distance traveled? 100 m Total displacement? 40 m
Let’s say you go 50 m east. 50 m east 10 m south Then you go 10 m south You have gone a distance of 60 m, but your displacement is less than that! You could find it by using the Pythagorean Theorem. Where the displacement is equal to the hypoteneuse.
Displacement is a vector. • Displacement has BOTH magnitude & direction. Vectors are represented with arrows. Displacement is represented with an X since it is along the x-axis. Displacement is then “the change in x” or x
Positive Displacement • Change in displacement is • x = x2 – x1 = 30 m – 10 m = 20 m
Negative Displacement • The person is walking in the opposite direction on the x-axis now • x = x2 – x1 = 10 m – 30 m = - 20 m The negative value here simply indicates a direction! (to the left)
SPEED VS. VELOCITY • Speed is a SCALAR quantity. It is defined as the total distance traveled divided by the time it takes to travel this distance. • s = total distance/total time • Velocity is a VECTOR quantity. It is defined in terms of displacement rather than total distance.
VELOCITY • AVG = TOTAL DISPLACEMENT VELOCITY TIME ELAPSED v = x t
Velocity is a function of time • Top: car is traveling at a constant velocity. • Bottom: car is traveling with a varying velocity