Speed and Velocity (12/10-12/14)

Distance-time graphs by BBC

Summary

Speed and Velocity may sound like very similar quantities, however, they have a very different meaning. Velocity has a direction. An example of velocity may be 40 m/hr north. This means that it is a vector quantity. However, speed only has a magnitude. an example of speed would be 40 m/hr. This means that it is a scalar quantity. The average speed is a measure of distance traveled in a given period of time. To measure the average speed, we can use a distance per time ratio.

For example, if we traveled 80 miles in 2 hours, we can create the following ratio:

80 miles / 2 hours, or 40 m/hr.

To represent the average speed, we can use a distance-time graph. On the horizontal, or x-axis, we write the time taken. In the example above, we would put 2 hours on the x-axis. On the vertical, or y-axis, we write the distance traveled. In the example, that would be 80 miles. Various lines on the graph mean different average speeds. This means that if an object is not moving, there will be a horizontal line. This is because the distance is not changing, however, time is still passing. If the line is steeper than the average speed is faster. This means that if a person is walking, the distance will still be increasing, but at a slower rate than if the person is running.

SP2: Developing and Using Models

This week, we used distance-time graphs to represent the average speed an object is moving at. By learning how to read this type of model, we were able to compare the speed during different time periods. We used the graphs to explain the distance per time ratio and see how different lines in the graph represent different speeds. Learning about distance-time graphs has helped me learn more about the distance per time ratio and has helped me visualize average speed.

XCC: Systems and System Models

This week in class, I observed a structure and function relationships in distance vs. time graphs. The structure and placement of lines and points on distance vs. time graphs affect how you interpret the movement and average speed of an object. The function of the graph depends on the structure because how you draw lines and points on the graph determines the average speed and movement. In the image above, the fact that the red line becomes straight and does not increase tells us that the object is stationary. This shows the structure of the distance vs. time graph. The structure leads to the function because this fact helps us infer that the object must have stopped moving for one reason or another. By learning about the structure and function of a graph, I have learned more about average speed.