# 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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### 33 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.

• SeungYi Sayo says:

I agree with your idea, and I thought of a simular idea, of somthing to hold, and release energy, (like your rubber band) but I think that a rubber band wouldn’t be very stable.

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.

• YunJi Kim says:

I strongly agree with your Rina, because your idea and my idea is really really similar. We both think that there’s something inside that car like the rubber band, and I agree that it stops by itself, when the rubbber band or something inside is getting slower. In addition, I want to give a compliment on your thinking, since you wrote your idea clearly, and give some evidence on your thinking.

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.

• Helena Eriksen says:

Why do you think the front and back wheels have a relationship?

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.

• Theresa krenn says:

There a rulakay is a spring inside the car. A coil spring. So far as I know.
When you pull it it stretch it and releasing it the spring snaps and the car goes forward.

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

What is an axel?

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.

• Gisele says:

I have a question and that is why do you think all of this because you didn’t say why

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.

• Amina says:

I think a spring is what was pullling the car

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.

12. Elena says:

I think that the pull back buggy works because of some sort of spring inside it. So if we pull the car back the spring would wound up as when we relice the car it pops and the car goes fast. It’s speed decreases.

13. SeungYi Sayo says:
• Chanmin Seo says:

I think there is spring inside the car which makes it move forward and when we stretch the spring backward it goes forward by that power of stretch in spring and when the spring come back to its original size it slows down and stop.

• SeungYi Sayo says:

I think the pull back car works by storing, and releasesing the energy.

I think the pullback car works like a slingshot because you pull it back to make it go forward. It’s almoost exactly how a slingshot works. I think that the wheels have some sort of spring making it move forward when pulled back.
Here is a link to my sketch:

15. arjan batra says:

I think that there is a rubber band inside of the car that connects the two wheels, and when it is pulled, the rubber band wraps up, and when you let go it suddenly snaps straight, and I think that is what makes it go.

• Arjan Batra says:
16. Theresa krenn says:

I am not sure how it works. My theory is that there maybe a rubber band around the wheels so if you pull it back it stretches and if you leave it it goes forward. Almost like a slingshot. Not really rubber bands but a internal coil spring. When the car gets released the spring unwinds and makes the car go forward. During the pullback energy is stored fast. But gets released slowly during the forward motion.

17. Soraia Capellan 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.

18. Alexander Zanetti - Olsen says:

I think there is a rubber band inside the car that wraps around some sticc and when youu let go it unravels and the car shoots forward.

19. Taiki says:

I think their is a big and long string and when you pull it the spring gets released and makes it go fast. I also think that the pull back car also works becuase the more you pull it the spring will get more stretched and then when you release it and then the car goes quick.

20. By the way, here is the website. |
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• rfrazier says:

Don’t see any website.

21. Rina Hamanishi says:
22. Yoochan Seo says:

I think the pullback car has some kind of spring or some kind of things that has elasticity. I am not so sure how it works, but I think as you pull the car back, it stretches the spring or anything, not until it’s limit of elasticity. And as you let go, it recovers its original shape, and while doing it, it triggers the wheels to go forward.

Very late. Sorry..