CHAPTER 27 – MOTION


EXAMPLE Question


Using the distance-time graph shown in Fig. 27.10, calculate the speed of the objects represented by lines A and B.


Solution


Both objects are represented by straight lines, which shows they are moving at a constant speed. To calculate speed, take any point on the graph and divide the distance value by the time value.


Time (s) Distance (m)


00 14


Speed (m/s)


ABAB 0 6


28 12 312 416


8 24


0 4 4 4 4


0 6 6 6 6


10 12 14 16 18 20 22 24 25


2 4 6 8


0 0 :Fig. 27.10


• The object represented by line A is moving at a constant speed of 4 m/s. • The object represented by line B is moving faster, at a constant speed of 6 m/s.


EXPERIMENTAL INVESTIGATION 27.1 How can we measure the speed of an object?


Equipment Trundle wheel


Method


1. Use a trundle wheel to mark out a straight line. Place tape (or a chalk mark) every 5 m, up to 35 m in total.


2. One student walks along the line while another student records their time with a stopwatch at each 5 m mark, until the end of the line.


3. Record the distance and time of the student in a table. Use the total distance and time to calculate the average speed.


4. Repeat with different students moving at different speeds and record in the table. 5. Compare each student’s overall average speed to their speeds at each marking. 6. Draw a distance-time graph to represent the data. 7. Compare the slope of each student’s graph to their average speed.


)Fig. 27.11 To measure the speed of an object


SAFETY • Make sure the area is clear.


• Wear appropriate clothing and shoes.


• Do not run too fast. Tape (or chalk) Stopwatch 1 2 3 Time (s) 4 5 6


B A


35 m


30m


25 m


20 m


15m


10 m


5m


Start j Go to page 79 of your Experimental Investigations Log to write up this investigation. Elements of Science 265


Distance (m)


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