Chapter 2. One Dimension Motion 2.1 Motion diagram 2.2 Distance and Displacement

Objectives: You are able to Draw motion diagram and describe motion. Understand a concept of particle model to present a moving object. Demonstrate your understanding of vector and scalar quantity and difference between distance and displacement. Show understanding of directions and signs for displacement.

Uniform motion in One Dimension: Motion is along a straight line (horizontal, vertical or slanted). The moving object is treated as though it were a point particle.

Describing Motion The study of one-dimensional kinematics is concerned with the multiple means by which the motion of objects can be represented. Such means include the use of words, graphs, equations, and diagrams.

Motion diagram A series of images showing the positions of a moving object at equal time intervals.

Particle model A simplified version of a motion diagram in which the object in motion is replaced by series of single points. To use the particle model, the size of the object must be much less than the distance it moves.

Practice Problems 1. Use the particle model to draw a motion diagram for a bike rider riding at constant pace. 2. Draw a constant motion diagram with seven dots. If it presents 12 s, how much time passed between adjacent dots. 3. Page 33, # 3 and 4

2.2 Where and When? Coordinate system: Origin Measurable straight line with numbers

A one-dimensional coordinate system You are free to choose the origin and positive direction as you like, but once your choice is made, stick with it.

Vector and Scalar Vector – quantities have magnitude and direction Scalar – quantities have only magnitude

Distance and Displacement Distance is the length of the actual path taken by an object. Consider travel from point A to point B in diagram below: Distance s is a scalar quantity (no direction): A B s = 20 m Contains magnitude only and consists of a number and a unit. (20 m, 40 mi/h, 10 gal)

Distance and Displacement Displacement is the straight-line separation of two points in a specified direction. A vector quantity: Contains magnitude AND direction, a number, unit & angle. (12 m, 300; 8 km/h, N) A B D = 12 m, 20o q

Distance and Displacement For motion along x or y axis, the displacement is determined by the x or y coordinate of its final position. Example: Consider a car that travels 8 m, E then 12 m, W. Net displacement D is from the origin to the final position: D 8 m,E x x = -4 x = +8 D = 4 m, W 12 m,W What is the distance traveled? 20 m !!

The Signs of Displacement Displacement is positive (+) or negative (-) based on LOCATION. The displacement is the y-coordinate. Whether motion is up or down, + or - is based on LOCATION. Examples: 2 m -1 m -2 m The direction of motion does not matter!

Practice problems What is distance and displacement after 4 sec. Page 37, # 7 and 8