Average Speed

Motion and Speed
Imagine you are at the grocery store. How would you describe where you are at any
moment in time? You might say that you are to the left of the bananas or that you are that
you are 1.0 m from the check-out lines. To describe the location of an object, you often
include distance and direction. Distance is the entire length of an object’s path. For
example, if you were to describe the location of your pencil, you might state that it is
10 cm to the left of your Science Notebook.

Position

When you describe an object’s location using distance and direction, you indicate its position. Position describes an object’s distance and direction from a reference point. A reference point is the starting point you choose to describe the location, or position, of an object. In the grocery store, your reference point
was the bananas or the check-out lines.

Astronomers often use the Sun as a reference point for objects in the solar system. To
describe the location of the Sun, however, astronomers select a different reference point.
Because the Sun is a star in the Milky Way galaxy, astronomers sometimes use the
galaxy’s center as a reference point.

GPS stands for Global Positioning System. Today, GPS is used worldwide in fields such as

farming, science, real estate, and for personal needs such as driving navigation and pet

loss prevention. GPS contains three components. First, satellites orbit Earth and

broadcast signals. Next, these signals are picked up by control and monitoring stations.

Lastly, the stations relay location to receivers owned by anyone in the world. Before GPS,

people relied heavily on maps, and even on the stars, to locate their position on the

globe. With GPS navigation, any person can locate where they are and in what direction 

they are headed.

Describing Motion
Think back to the grocery store. As you search for the items you need to purchase, you
change your position within the store. The process of changing position is called motion.
There are different ways to describe an object’s motion. One way is to describe a
change in the object’s distance or direction, such as, “A car drove 3.0 km north from the
school.” You can also describe the time it took for the object’s position to change. Time is
the measurable period during which something takes place. When you describe to a
friend that it took 2 h to travel to a vacation destination, you are describing your motion.

Speed
When you describe an object's motion, you can discuss its speed. Speed is a measure of
the distance an object travels in a given amount of time. An object's speed can be
constant or changing. When an object's speed changes, it is often helpful to calculate its
average speed. Average speed is equal to the total distance traveled divided by the
total time taken to travel that distance. To calculate average speed, you need to make
Measurements.

Calculating Average Speed
Average speed is a calculated quantity, which means it cannot be measured directly.
Instead, you need to measure the total distance the object travels and the total time it
takes to travel that distance. Then you calculate the average speed using the following
Equation,

Interpreting Average Speed
When an object moves at a constant speed, its average speed for each time interval is
the same. That means for every second, the object travels the same distance. When an
object's speed changes, the average speed for each time interval is different.

Changing Speed

When an object changes speed, the distance it travels each second changes. The
distance of an object that speeds up will increase each second. The distance of an
object that slows down will decrease each second.