We will begin our study of physics with a study of motion. 

Look around you, and you will find that almost everything is in motion: flying birds, running people, falling books, etc. We will analyze their motions and think about how fast the object moves and how far. 

1. Distance and Displacement
2. Average Velocity and Instantaneous Velocity
3. Position-time Graph
4. Velocity-time Graph
5. Relative Motion
6. Chapter 2 Quiz

Distance and displacement are different. When you traveled 50 km to the East and then 20 km to the West, the total distance you traveled is 70 km, but your displacement is 30 km East. 

In physics, we say that distance is a scalar and displacement is a vector. Scalar has a magnitude and vector has both a magnitude and a direction. Scalar is one dimensional and vector is two dimensional. 

Velocity shows how fast an object is moving in which direction. Average velocity can be calculated by dividing displacement over time. 

For example, when a car moved 50 km in 2 hours, the average velocity is 25 km/h because . 

The instantaneous velocity shows the velocity of an object at one point. For example, when you are driving a car and its speedometer swings to 90 km/h, then the instantaneous velocity of the car is 90 km/h. 

A position-time graph simply shows the relationship between time and position. From the following data, for example, 
 

time (s)	0	1	2	3	4	5
position (m)	0	20	50	130	150	200

You can draw the following graph: 

The tangent of a position-time graph represents velocity since 

A velocity-time graph shows the relationship between velocity and time. For example, if a car moves at constant velocity of 5 m/s for 10 seconds, you can draw a velocity-time graph that looks like this: 

The area below the line represents the displacement the object traveled since it can be calculated by x * y, or (time * velocity) which equals to displacement. 

When car A moves at 50 km/h and car B moves at 30 km/h in opposite direction, the velocity of car A relative to car B is 80 km/h. 

Take the Chapter 2 Quiz to see how well you can do!