com www.GOALias.blogspot.com www.GOALias ... - fun learning

www.GOALias.blogspot.comwhen compared to the data presentedby a table. For example, Table 13.5 givesinformation about the distance movedby the bus only at some definite timeintervals. On the other hand, from thedistance-time graph we can find thedistance moved by the bus at anyinstant of time. Suppose we want toknow how much distance the bus hadtravelled at 8:15 AM. We mark the pointcorresponding to the time (8:15 AM) onthe x-axis. Suppose this point is A. Nextwe draw a line perpendicular to thex-axis (or parallel to the y-axis) atpoint A. We then mark the point, T, onthe graph at which this perpendicularline intersects it (Fig. 13.14). Next, wedraw a line through the point T parallelto the x-axis. This intersects the y-axisat the point B. The distancecorresponding to the point B on they-axis, OB, gives us the distance in kmcovered by the bus at 8:15 AM. How mucis this distance in km? Can you nowhelp Paheli to find the distance movedby the bus at 9:45 AM? Can you alsofind the speed of the bus from itsdistance-time graph?KeywordsBar graphGraphsNon-uniform motionOscillationSimple pendulumSpeedTime periodUniform motionUnit of timeWhat you have Learnt• The distance moved by an object in a unit time is called its speed.• Speed of objects help us to decide which one is moving faster than theother.• The speed of an object is the distance travelled divided by the time takento cover that distance. Its basic unit is metre per second (m/s).• Periodic events are used for the measurement of time. Periodic motion ofa pendulum has been used to make clocks and watches.• Motion of objects can be presented in pictorial form by theirdistance-time graphs.• The distance-time graph for the motion of an object moving with a constantspeed is a straight line.155MOTIONAND TIME155