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Gravity
Himalayas
Distance time graph
The change in the position of an object with time can be represented on the distance-time graph adopting a convenient scale of choice.In this graph, time is taken along the x–axis and distance is taken along the y-axis.Distance-time graphs can be employed under various conditions where objects move with uniform speed, non-uniform speed, remain at rest etc.
Distance-time graph of an object moving with uniform speed
We know that when an object travels equal distances in equal intervals of time, it moves with uniform speed. This shows that the distance travelled by the object is directly proportional to time taken.Thus, for uniform speed, a graph of distance travelled against time is a straight line, as shown in the above figure.The portion OB of the graph shows that the distance is increasing at a uniform rate.
We can use the distance-time graph to determine the speed of an object. To do so,consider a small part AB of the distance-time graph shown in the above figure.Draw a line parallel to the x-axis from point A and another line parallel to the y-axis from point B. These two lines meet each other at point C to form a triangle ABC.Now, on the graph, AC denotes the time interval (t2 – t1) while BC corresponds to the distance (s2 – s1).
We can see from the graph that as the object moves from the point A to B,it covers a distance (s2 – s1) in time (t2 – t1). The speed, v of the object, therefore can be represented as v= (s2 – s1) / (t2 – t1)
Valency
Valency is the combining capacity of an element. Valency can be used
to find out how many atoms of an element will combine with the other
element to form a chemical formula. For example, hydrogen has a valency
+1 and chlorine has a valency –1, so one atom of hydrogen combines with
one atom of chlorine to form hydrochloric acid (HCl). Oxygen has a
valency –2, so one atom of oxygen combines with two atoms of hydrogen to
form water molecule (H2O).