Chapter 1: The Science of Physics  1.1 The Science of Physics  1.2 Scientific Inquiry and Natural Laws  1.3 The Nature of Scientific Knowledge

1.3 The nature of scientific knowledge  Scientific knowledge grows by systematically extending simple explanations to include more complex situations.  Explanations can be qualitative or quantitative and tell you why or how much.

1.3 Models  The most useful form of scientific knowledge is a model.  One type of model is a graph.  This graphical model shows how a rolling cart’s speed changes as it goes downhill.

1.3 Models  The second form of simple model is a formula.  Formulas are more powerful models than graphs because they can include more than two variables and have a much wider range of values.

1.3 Models  A model tells you precisely how the variables in a system are related to each other.  A system is a group that we choose to include all the variables we are interested in that affect each other.

1.3 Problem Solving Techniques  Step 1  Determine what the problem asks you to find.  Step 2  Identify the information you are given.  Step 3  Identify laws or relationships.  Step 4  Apply the given information and the relationships.

Calculating time from speed and distance  How long does it take to travel 2,000 kilometers at a speed of 100 kilometers per hour?

Calculating time from speed and distance  Step 1  You are asked to find time.  Step 2  You are given the distance in km and speed in km/h.  Step 3  Time is distance ÷ speed.  Step 4  Time = 2,000 km ÷ 100 km/h = 20 h

1.3 A good theory that started out wrong  An early theory of fire proposed that all materials contained a substance called phlogiston, which was released during burning.  The careful work of Antoine Lavoisier (1743–1794) finally disproved the phlogiston theory.  Lavoisier showed that as a metal burned, it increased in weight because it gained oxygen.  While the phlogiston theory was not correct, it led to the discovery of oxygen.

1.3 Scientific knowledge and the solar system Early civilizations believed the Earth was covered by a dome on which the sun, stars and planets moved. In the Middle Ages, people thought the sun, stars and planets circled the Earth. Today we know the earth and planets orbit the sun.