Describing Motion Physics 11

Cartesian Coordinates When we describe motion, we commonly use the Cartesian plane in order to identify an object’s position This is simply the x-y plane that you are familiar with from math class

Cartesian Coordinates When considering an object in Cartesian Coordinates, it is important to determine a reference (zero) point This is often where the object starts but can be any point that is convenient Regardless of the reference point, all calculations will give the same result

Position-Time Graph A position-time graph is one that generally has position on the y-axis and time on the x-axis We will normally use metres for position and seconds for time

Gebrselassie At the Berlin Marathon in 2008, Ethiopian Haile Gebrselassie set a new world record for the marathon with a time of 2:03:59. The key to Gebrselassie’s success is his ability to maintain a constant pace through out the event. His split times for each 5000m interval (and half marathon and marathon splits) are given below. d(km)t(s)

1. Using the data table, plot his position (d) on the y-axis and his time (t) on the x-axis. Ensure that you choose a scale that will enable you to use as much of the graph paper as possible. 2. Using the data, draw a line of best fit to the data and determine the slope of the line. What are the units for the slope in this instance? 3. For each 5km split (you can ignore the 21.1km and 42.2km) calculate his average speed in m/s by dividing the distance in metres by the time in seconds. 4. Compare the results for each segment in part 3 with the result for part 2. What do you notice? What you can say about his pacing?

Apply Obtain a car, metre stick and stop watch In your group, choose a starting point and record the location after every second (with a person) Measure the distance from the start point to each person Repeat recording position every two seconds Plot two position-time graphs and find the equation for the lines of best fit