Unit 2 1 Dimensional Motion

 Mechanics – the study of how objects move and respond to external forces  Kinematics – study of motion with no concern for the cause Motion

 Perceiving motion is instinctive— your eyes pay more attention to moving objects than to stationary ones. Movement is all around you.  Movement travels in many directions, such as the straight-line path of a bowling ball in a lane’s gutter, the curved path of a tether ball, the spiral of a falling kite, and the swirls of water circling a drain.  When an object is in motion, its position changes. Its position can change along the path of a straight line, a circle, an arc, or a back-and-forth vibration. Motion

 A description of motion relates to place and time. You must be able to answer the questions of where and when an object is positioned to describe its motion.  In the figure below, the car has moved from point A to point B in a specific time period. Motion

Particle Model

Relative Motion

 A) What is your speed relative to the ground?  100 km/h  B) What is your speed relative to the seat you are sitting in?  0 km/h  C) What is the speed of the fly relative to you?  0 km/h Relative Motion

 A coordinate system tells you the location of the zero point of the variable you are studying and the direction in which the values of the variable increase.  The origin is the point at which both variables have the value zero. Coordinate System

 In the example of the runner, the origin, represented by the zero end of the measuring tape, could be placed 5 m to the left of the tree.  The motion is in a straight line, thus, your measuring tape should lie along that straight line. The straight line is an axis of the coordinate system. Coordinate System

 You can indicate how far away an object is from the origin at a particular time on the simplified motion diagram by drawing an arrow from the origin to the point representing the object, as shown in the figure. Coordinate System

 Coordinate System – define an origin and a positive direction  Must remain consistent  In one dimension  Typically to the right is positive, left is negative Coordinate System

Position – a reference to the coordinate system

Coordinate System

Vectors and Scalars

Speed and Velocity- Speed is a scalar quantity. It only contains magnitude (number). Ex. 50 mph Velocity is the vector quantity. It contains both magnitude and direction. Ex. 50 mph N Vectors and Scalars

 Distance and Displacement  Distance is the total length traveled from beginning to end. It is a scalar quantity (magnitude only). Ex. 14 m  Displacement is the position in reference to the origin. It is a vector quantity and includes both magnitude and direction. Ex. 14 m N Vectors and Scalars

 Distance is 84.5 m, displacement is 84.5 m E. Vectors and Scalars

Distance traveled is m, displacement is 24.5 m E. Vectors and Scalars

Velocity

 Average velocity  Defined as the total distance over the total time  Used when determining ETA by GPS; over long trips Velocity

 Instantaneous Velocity  Velocity at any instant in time.  Measured by your speedometer in your car  Used by police to issue tickets Velocity

 Constant Velocity  Velocity that is unchanging  Speed of sound, speed of light, cruise control Velocity

Acceleration