# 5 October Science 7 Changing speeds and more

B. Review previous DSN entry.

C. Preview blogpost for the day.

D. Create new DSN entry for the day. (Motion folder)

E. Questions.

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“As a boy, I was fascinated by speed, by the wild range of speeds in the world around me. People moved at different speeds; animals so much more so. The wings of insects moved too fast to see, though one could just their frequency by the tone they emitted–a hateful noise, a high E, with mosquitoes, or a lovely bass hum with the bumblebees that flew around the hollyhocks each summer. Our pet tortoise, which could take an entire day to cross the lawn, seemed to live in a different time frame altogether. But what then of the movement of plants? I would come down to the garden in the morning and find the hollyhock a little higher, the roses more entwined around their trellis, but, however patient I was, I never could catch them moving.”

Oliver Sacks in “Speed,” an essay from The River of Consciousness (2017). Picador.

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Finish investigation of pullback car from previous class.

A. Make a new group of 3. These should be students you have not worked with before (or have worked with the fewest number of times). Update your collaboration chart / document. Names, topics, activities, dates, links (relevant blogposts, DSN entries, group documents and data)

You will receive a pullback car. Explore its operation. Do not overstretch the spring, but do find the point that gives maximum acceleration and distance. Do a trial run without measuring. Each student separately make a sketch graph (distance vs. time) of how you think the motion would look. Discuss with your group your ideas using your sketch graph to illustrate your point. Make sure you have a rich entry for the section “what we talked about” in your DSN entry.

Design a track (frame of reference) to evaluate how the speed changes. This will be very similar to your tumble buggy procedure. Find the times to reach various distances. Make a distance vs. time graph to display your results. Calculate the average speed for zero meters to the maximum distance you measure. Can you find average speeds for other segments, like from 0-1, 1-2, and 2-3 meters?

Compare a graph that shows average speeds from 0-1, 0-2, and 0-3 meters with a graph that shows average speeds for 0-1, 1-2, and 2-3 meters.

What happens to the graph if average speeds are found for smaller and smaller segments of distance and time?

Be prepared to share your findings with the rest of the class.

***All students: Reply to today’s blogpost. Describe how you think the pullback car works. What  do you think makes the car change its speed from 0 m/s to the other speeds you observe during a trip? What is the mechanism do you think? Make a sketch of your imagined mechanism and add link to blog–with sharing so that anyone with the link can view. Be sure the response that you submit on the blog is also copied into your DSN entry for the day.

Reply to another student’s comment. Ask a clarifying question about their sketch and the mechanism they have proposed.

B. Thought problem. Answer with a sketch graph (distance vs. time) and description. If a cart is pulled with a constant force, what motion do you think will result?

C. We shall watch and discuss in detail the motion examples presented in: Frames of Reference < https://www.youtube.com/watch?v=bJMYoj4hHqU >. What is your understanding of the statement, “All motion is relative?” If we do not have time to watch this as a class, watch on your own. Have your questions ready. Be prepared for a quiz in an upcoming class.

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### 11 Responses to 5 October Science 7 Changing speeds and more

1. HyunJoon Hwang says:

I think there is a rubber thing inside the car and when we pull the car, it get stretched and it goes forward when we take our hands off. The car gets slower as it goes because when it gets slower, it means that the power of pulling rubber band is getting done.

2. Jaein Lee says:

I think there is a rubber band inside of the car (at the back wheels), and when we pull the car back,the rubber band curl up on the back wheels, and then when we released the car, the rubber band will be released and after there is no more rubber band to be releases, the car will finally stop.

3. Rina Hamanishi says:

I think that the pullpack car works like it because as you’re pulling back the car, something inside which is probably connected to the wheel makes it tighter, so when u release it moves forward in that speed depending on how far you moved it back. Also as soon as you release the car, the speed will become slower and slower, and finally stop by itself.

4. YunJi Kim says:

In my thinking, this rubber band inside the car will change a lot when we are moving the car. To begin with, I think the rubber band will place near by back wheel and connected by front wheel, since I think back wheels and front wheels has some kind of relationship with each other. So when we are pulling this car back, the rubber band will be tightly with each other and a bit tilt at the back part, and in other words, we are pulling the car back. And when we release the car to go front or to move, the rubber band will bounce back and forth because of some kind of pressure that we put threw the rubber band. Lastly, after some second, it will back to normal, since it’s rubber band is going back to normal after few seconds.

5. Minjun Kim says:

I think there is a spring inside of the car and when we pull the car,spring is wound up andwhen we released the car,the spring will be released and if spring is almost done to released then care became slower.

6. Gisele says:

I think that the pull back car works because I think there is a spring and when you pull that spring really far it starts to pop to insure you that you are taking it to far. And when you release the pull back car it will go super fast and slow down when the spring isn’t far back anymore.

7. Jake Boucher says:

I think that inside the car there is a wind of string attached to a spring. The string is wound around the axel of the car back wheels. As you pull back the car the string is wound around the string as the wheel turns and as you let go the spring pulls the string in the opposite direction making it go further

8. Seojin Yoon says:

I think there is metal stick that is between two wheels and in the middle of the stick, there is not moving wheel. And that wheel and other wheel is connected with a rubber band.

9. Amina says:

I think that the car will not have constant speed because at some point the car will have to slow down so it can stop so while it slows down the speed changes and it is not constant velocity.

10. Samika says:

I’m convinced that the pullback car works because, like the elephant, it’s about cause and effect. So I think that the pullback car has a band or some kind of thing holding it back until we pull it back and then realise it so that the car can go at its fastest and then slow down again once the bad/whatever it is goes off or comes to a stop. So for the band to work or for the pullback car to release we need to pull it back.

11. Helena Eriksen says:

In think there is something that’s gathering pressure inside the car when you pull it back. When you release it, that pressure will slowly go out, then the pressure will be released consistently for a while, then the pressure will run out, and then it slows down till it stops.