# 5 September Science 7 Graphs of staged races continued; calculating and understanding average speed; concepts of velocity; relative motion

Opening routine:

1. Mindful moment. “Breath is the bridge which connects life to consciousness, which unites your body to your thoughts. Whenever your mind becomes scattered, use your breath as the means to take hold of your mind again.” Thich Nhat Hanh
2. Review DSN entry from past class. Is it complete? If not, what is missing? Write this. Is it organized? If not, what would help it become organized? Could another person ready your DSN and makes sense of it? What questions do you think they might have?
3. Browse today’s blogpost.
4. Create a new document in your DSN folder and in your Motion folder for today. Give the document a file name that includes the date and a word or phrase that indicates what the entry is about. Be sure to include a link to the specific blogpost for the day in your DSN entry. Let Dr. F know when you have this uploaded.
5. Your questions. Consider writing your own questions as well as the questions your classmates have. Record the responses.
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Review graphs.

3 steady pace motions–walk, jog, run.

Slow to fast and fast to slow.

Tortoise and hare.

To what extent did the movers move with constant speed?

When a line segment of a distance vs. time graph is straight, there is an assumption of constant speed.

Drawing a straight line from one point to another is an assumption that there was a constant speed–even if that is not known. The idea of average speed is like an assumption of constant speed. The assumption might not be true but it can be helpful.

Average speed is what the speed of the mover would have been if she/he/it had constant speed for the interval in question.

Average speed = distance travelled / time elapsed     or

Average speed = change in position / change in time

The slope of a straight line segment on a distance vs time graph is equal to the average speed for the interval in question.

You may find your mind pulled toward some older understanding of the term “average.” This is similar to the backwards bike. You may have to modify an old understanding in order to acquire the new one. This is what learning and school is all about.

Velocity is a quantity that includes both speed and direction.

Instantaneous velocity is the speed and direction at a particular instant in time. We will use an experience you can have riding in a vehicle to give you a picture of what instantaneous velocity means.

Constant velocity = same speed in a straight direction

Changing velocity = speeding up or slowing down or turning

Acceleration = change in velocity / change in time

Frame of reference is an essential idea and tool for observing and understanding motion.

All motion is relative. One needs to specify the frame of reference in describing the motion of an object.

What is the average speed for the slow to fast and the fast to slow? What would their graphs look like if they both had the same average speed for the entire 25 meter event? What were their average speeds for the first 5 meters? For the last 5 meters?

In the tortoise and hare graphs, what do you think of this statement: “The tortoise and the hare have the same average speed for the 25 meter event”? What is the value of the average speed. Explain.

Explain the difference between time and speed.

We will watch and discuss this together: