Each point on the graph represents a certain time in the journey and the speed of the skier at that time. Joining the points on the graph with a line shows the relationship between time and speed throughout the journey. We can now use this line graph to find the speed of the skier at any time during the journey. We can also use the graph to calculate the acceleration of the skier at any time. Since acceleration is a change in speed we need to use two different points on the graph. For example, the point on the graph representing 5 s also represents the speed 10 m s -1 the speed of 20 m s-1
Time (s) Fig. 10 Speed versus Time. . The point representing 10 s represents . We are able to obtain this information from the graph even though it is not given in the
table of figures. We calculate the acceleration as follows: Speed after 5 s = 10 m s-1 Speed after 10 s = 20 m s-1
Acceleration =
Change in velocity Time taken
=
Change in speed = 10 m s-1 Time taken = 5 s
10 m s-1 5 s
= 2 m s-2 Nature of Science
In this chapter we learned about the relationship between mass, volume and density. We also learned about the relationship between distance, time and speed. A lot of of scientific research is about trying to find out if there is a relationship between different things, for example smoking and lung cancer, or CO2
emissions and global warming.
Questions 1. Think of as many relationships between different things as you can. How many of them do you think have been scientifically proven?
2. What exactly do people mean when they say that a relationship between two things has been scientifically proven?
3. Can you think of a situation where something was widely accepted as being true but was then found not to be true? Explain how this happened.
Chapter Summary
1. 2. 3. 4. 5. 6.
The density of a substance is its mass per unit volume. An object floats because its density is less than the density of the liquid it is in. The speed of an object is the distance travelled per unit time Velocity is the speed of an object in a particular direction. Acceleration is the change in velocity per unit time. Deceleration is when velocity decreases.
