Unit 2 1 Dimensional Motion Motion Mechanics the

Unit 2 1 Dimensional Motion

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.

Particle Model

Relative Motion

Relative Motion

Relative Motion

Relative Motion

Relative Motion

Relative Motion

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

Coordinate System 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 – 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

Coordinate System

Vectors and Scalars

Vectors and Scalars

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 84. 5 m, displacement is 24. 5 m E.

Velocity

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

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

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

Acceleration