2.1 Describing Motion - Weebly

2.1 Describing Motion

Using Coordinate Systems

Coordinate System ? The frame of reference used to describe a system or event. ? Can be used to visualize a system before doing calculations and solving the problem.

One-Dimensional Coordinate Systems ? A straight line with an arrow at the end, indicating the positive direction. ? For horizontal motion, we will use an x-axis. ? When setting up a coordinate system, you can choose the origin point (where x = 0) and the positive direction (the direction in which x increases).

Position and Motion ? We can use different values of x to describe different positions on our coordinate system. o x = 0 ? origin point o xi ? initial position (before moving) o xf - final position (after moving) ? See Figure 2.1 on page 44

Distance/Displacement

Distance ? The total length of the path that is taken on a trip. ? Describes exactly how much you have traveled. ? Distance is a scalar, a quantity represented by a number and a unit, with NO direction. ? To calculate total distance traveled, add up each of the distances you traveled along the way, regardless of direction.

Displacement ? The change in the position of an object. ? Describes how far away you are from where you started.

? Displacement is a vector, a quantity with both a number and a unit AND a direction.

? To calculate total distance traveled, subtract the initial position from the final position. o = - ? x ? displacement (the symbol represents a "change") o Pronounced "delta x" o Can be positive or negative depending on the direction an object moves. ? xf ? final position ? xi ? initial (starting) position

Distance vs. Displacement

Distance and displacement use the same units, but the distance travelled and displacement may not always be the same.

Examples

x = 0 Origin

100 m

x = 100 m

150 m

x = 250 m

? South Dorm School Cafeteria o Distance ? distance = 100 m + 150 m = 250 m o Displacement ? = - = 250 m - 0 m = 250 m

? South Dorm School Cafeteria School o Distance ? distance = 100 m + 150 m + 150 m = 400 m o Displacement ? = - = 100 m - 0 m = 100 m

? South Dorm School South Dorm o Distance ? distance = 100 m + 100 m = 200 m o Displacement ? = - = 0 m - 0 m = 0 m ? =

? Cafeteria School South Dorm o Distance ? distance = 150 m + 100 m = 250 m o Displacement ? = - = 0 m - 250 m = -250 m ? The negative value shows that you are moving towards your origin point.

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