2014. 3.26
6.What is rotational inertia, and is it similar to inertia as studied in previous chapters?
The property of an object to resist changes in its rotational state of motion is called rotational inertia. Compare to the inertia that we studied in previous chapter, they have part that is the same. They both depend on mass.
7.Inertia depends on mass: rotational inertia depends on mass and something else. What?
It also depends on the distribution of the mass about the axis of rotation.
8.Does the rotational inertia of a particular object differ for different axes of rotation? Can one object have more than one rotational inertia?
Yes. I guess since the rotational inertia of one object will change according to different axes of rotation, it can have more than one rotational inertia.
9.Consider three axes of rotation for a pencil: along the lead, at right angles to the lead at the middles, at right angles to the lead at one end. Rate the rotational inertias about each axis from small to large.
The greater the distance between an object’s mass concentration and the axis, the greater the rotational inertia. Along the lead<middle<at one end.
10.Which is easier to get swinging, a baseball bat held at the end or one held close to the massive end (choked up)
Helding close to the massive end will be easier to get swinging
11.Why does bending your legs when running enable you to swing your legs to and for more rapidly?
Bending legs can reduce the rotational inertia, so people can run more rapidly.
12. Which will have the greater acceleration rolling down an incline, a hoop or a solid disk?
Solid disk will have the greater acceleration than a hoop, because hoop has greater rotational inertia.
13. what does a torque tend to do to an object?
Force tends to change the motion of things and twist or change the state of rotation of things.
14. what is meant by the “lever arm” of tongue?
The distance that provides leverage.
15. how do clockwise and counterclockwise torques compare when a system is balance?
16. if you toss a stick into the air, it appears to wobble all over the place. Specifically, what place?
Center of mass.
17. where is the center o mass of a soccer ball? Where is its center or gravity? Where are these centers for a baseball bat?
Center of mass of a soccer ball should be at it’s geometrical center. Center of gravity is also at it’s geometrical center.
Center of mass of a bat should be close to the thicker part. center of gravity is also at it’s geometrical center.
18. if you hang at rest by your hands from a vertical rope, where is your center of gravity with respect to the rope?
Maybe in the midpoint of the rope.
19. where is the center of mass of a soccer ball?
In its geometric center.
p145 (1-4)
1. B>C>A
2. C>B>A
3. B,A,C
4. A>C>B
P149(1,2,3,4)
1. The mouth wil roll faster, it will roll triple.
2. (a) 80*0.25=20
(b) 80*0.25/0.1=200
(c)Yes.
3. 25*3/35=3kg
4. 75-50=25
100-50=50
The property of an object to resist changes in its rotational state of motion is called rotational inertia. Compare to the inertia that we studied in previous chapter, they have part that is the same. They both depend on mass.
7.Inertia depends on mass: rotational inertia depends on mass and something else. What?
It also depends on the distribution of the mass about the axis of rotation.
8.Does the rotational inertia of a particular object differ for different axes of rotation? Can one object have more than one rotational inertia?
Yes. I guess since the rotational inertia of one object will change according to different axes of rotation, it can have more than one rotational inertia.
9.Consider three axes of rotation for a pencil: along the lead, at right angles to the lead at the middles, at right angles to the lead at one end. Rate the rotational inertias about each axis from small to large.
The greater the distance between an object’s mass concentration and the axis, the greater the rotational inertia. Along the lead<middle<at one end.
10.Which is easier to get swinging, a baseball bat held at the end or one held close to the massive end (choked up)
Helding close to the massive end will be easier to get swinging
11.Why does bending your legs when running enable you to swing your legs to and for more rapidly?
Bending legs can reduce the rotational inertia, so people can run more rapidly.
12. Which will have the greater acceleration rolling down an incline, a hoop or a solid disk?
Solid disk will have the greater acceleration than a hoop, because hoop has greater rotational inertia.
13. what does a torque tend to do to an object?
Force tends to change the motion of things and twist or change the state of rotation of things.
14. what is meant by the “lever arm” of tongue?
The distance that provides leverage.
15. how do clockwise and counterclockwise torques compare when a system is balance?
16. if you toss a stick into the air, it appears to wobble all over the place. Specifically, what place?
Center of mass.
17. where is the center o mass of a soccer ball? Where is its center or gravity? Where are these centers for a baseball bat?
Center of mass of a soccer ball should be at it’s geometrical center. Center of gravity is also at it’s geometrical center.
Center of mass of a bat should be close to the thicker part. center of gravity is also at it’s geometrical center.
18. if you hang at rest by your hands from a vertical rope, where is your center of gravity with respect to the rope?
Maybe in the midpoint of the rope.
19. where is the center of mass of a soccer ball?
In its geometric center.
p145 (1-4)
1. B>C>A
2. C>B>A
3. B,A,C
4. A>C>B
P149(1,2,3,4)
1. The mouth wil roll faster, it will roll triple.
2. (a) 80*0.25=20
(b) 80*0.25/0.1=200
(c)Yes.
3. 25*3/35=3kg
4. 75-50=25
100-50=50
circular motion (2014.3.19)
Review Qestion:
1.What is meant by tangential speed?
Tangential speed is the leaner speed and it's unit is (m/s) . It's the extra speed of linear speed.
2.Distinguish between tangential speed and rotational speed.
Ther units are different, tendential speed is m/s but rotational speed is RMP. Tangential speed is similar to linear speed but rotational speed is the amount if revolution.
3.What is the relationship between tangential speed and disctance from the center of the rotational axis?
When the distance is bigger, the tangential speed will be also bigger.
For example the tngential speed when the radial distance is 10 meters will be bigger than which with the disctance of 5 meters.
Exercise:
1.They have same rotational speed, but he has slower tangential speed, because there is no relationship between radial disctance and the rotational speed.
3. Since rotational speed has no relationship with radial distance, rotational speed will not change because of the different diameter.
The wheel with bigger diameter has bigger tangential speeds.
1.What is meant by tangential speed?
Tangential speed is the leaner speed and it's unit is (m/s) . It's the extra speed of linear speed.
2.Distinguish between tangential speed and rotational speed.
Ther units are different, tendential speed is m/s but rotational speed is RMP. Tangential speed is similar to linear speed but rotational speed is the amount if revolution.
3.What is the relationship between tangential speed and disctance from the center of the rotational axis?
When the distance is bigger, the tangential speed will be also bigger.
For example the tngential speed when the radial distance is 10 meters will be bigger than which with the disctance of 5 meters.
Exercise:
1.They have same rotational speed, but he has slower tangential speed, because there is no relationship between radial disctance and the rotational speed.
3. Since rotational speed has no relationship with radial distance, rotational speed will not change because of the different diameter.
The wheel with bigger diameter has bigger tangential speeds.
Catapult design activity-reflections (2014.2.25)
Describe how you contributed to your team, what did you do, were their any major contributions you are especially proud of?This time, the job I did was a helper. We used a lot of tape to make our device more stable.
Did your team apply the EDP successfully? (i.e. did you identify the problem & constraints, brainstorm solutions, test and prototype a solution, refine the design).
Our team didn’t apply the EDP very well. At first we thought our team can have the best score, but at last our ball threw too high and that hit the ceiling, so we didn’t have very good score.
What changes did your team make to your design?
We added one stick in front of the top stick to make the ball throw farther.
what worked well in your design? Identify what did not work so good.
Our device is very stable, that’s the best part. But the worse part is, we can’t throw the ball father. I still can’t figure out why out device can’t have a better score.
Describe any energy conversions/forces/motions/Newton’s laws that apply to a catapult mechanism.
Elastic potential energy is in the rubber band, since we have to pull it first and then release it. During this process, there is elastic potential energy. Then elastic potential energy transform into kinetic energy. Gravity is also in this catapult mechanism. The ball finally hit the ground is because of the gravity. The ball also has law of inertia. Law of inertia can help the ball keep the movement
Did your team apply the EDP successfully? (i.e. did you identify the problem & constraints, brainstorm solutions, test and prototype a solution, refine the design).
Our team didn’t apply the EDP very well. At first we thought our team can have the best score, but at last our ball threw too high and that hit the ceiling, so we didn’t have very good score.
What changes did your team make to your design?
We added one stick in front of the top stick to make the ball throw farther.
what worked well in your design? Identify what did not work so good.
Our device is very stable, that’s the best part. But the worse part is, we can’t throw the ball father. I still can’t figure out why out device can’t have a better score.
Describe any energy conversions/forces/motions/Newton’s laws that apply to a catapult mechanism.
Elastic potential energy is in the rubber band, since we have to pull it first and then release it. During this process, there is elastic potential energy. Then elastic potential energy transform into kinetic energy. Gravity is also in this catapult mechanism. The ball finally hit the ground is because of the gravity. The ball also has law of inertia. Law of inertia can help the ball keep the movement
Engineering design (2014.2.16)
1. What did you contribute to your team?
I helped the engineer and the scientist build the tower. Like some times, I helped hold the foundation, to make the engineer easier to build the upper level. Since before you stick the upper level of the tower, the foundation was very unstable.
2. What do you think engineers have to consider when they suggest which materials would be best for a certain structure?
The engineer has to think about whether this material will make the tower stable or not. In our group, we had a question on we should use strings or tapes to connect each spaghetti. We tried the string first, we think if the string will work it’s more stable but it will take more time. At last, considering about the time, we chose to use tape to stick the spaghetti together
3. What forces cause the tower to tip over?
I think it is the gravity and the mass of tape cause the tower to tip over. In our group, we used more tape on the right side, because it’s very hard to stick the spaghetti together. At last about 7 minutes later, it fell to the right.
4. What features of the design helped your tower to reach new heights?
I think it is the shape we chose. We chose the triangle to be the foundation shape. We knew triangle is the most stable shape and a good foundation help the tower a lot to reach new heights.
5. After testing what changes did you make to your tower?
We changed the way we sticked the spaghetti. At first we used string, it was too hard to stick the spaghetti and also took too much time so at last we chose the tape instead of the string.
6. Engineers early ideas rarely work out perfectly, How does testing help improve your design?
The idea first we came up was making several cube and sticked them together but we have limited spaghetti, limited tape and only 30 minutes. Triangle will take less spaghetti since it only has three edges. The testing will make out plan more perfect, let us think more about how to use less materials and make high height.
7. What did you learn from watching others?
Out product was more traditional, we only had one shape. After watching others, we saw many groups combined the triangle and rectangle.
I helped the engineer and the scientist build the tower. Like some times, I helped hold the foundation, to make the engineer easier to build the upper level. Since before you stick the upper level of the tower, the foundation was very unstable.
2. What do you think engineers have to consider when they suggest which materials would be best for a certain structure?
The engineer has to think about whether this material will make the tower stable or not. In our group, we had a question on we should use strings or tapes to connect each spaghetti. We tried the string first, we think if the string will work it’s more stable but it will take more time. At last, considering about the time, we chose to use tape to stick the spaghetti together
3. What forces cause the tower to tip over?
I think it is the gravity and the mass of tape cause the tower to tip over. In our group, we used more tape on the right side, because it’s very hard to stick the spaghetti together. At last about 7 minutes later, it fell to the right.
4. What features of the design helped your tower to reach new heights?
I think it is the shape we chose. We chose the triangle to be the foundation shape. We knew triangle is the most stable shape and a good foundation help the tower a lot to reach new heights.
5. After testing what changes did you make to your tower?
We changed the way we sticked the spaghetti. At first we used string, it was too hard to stick the spaghetti and also took too much time so at last we chose the tape instead of the string.
6. Engineers early ideas rarely work out perfectly, How does testing help improve your design?
The idea first we came up was making several cube and sticked them together but we have limited spaghetti, limited tape and only 30 minutes. Triangle will take less spaghetti since it only has three edges. The testing will make out plan more perfect, let us think more about how to use less materials and make high height.
7. What did you learn from watching others?
Out product was more traditional, we only had one shape. After watching others, we saw many groups combined the triangle and rectangle.
october 11th homework!
Why was the calorimeter
insulated?
Because in our experiment, we want to find out, how long will it take if the temperature raises 10 degree. It’s about the heat, if it’s not insulated, that means you don’t have a layer of other materials inside it to protect from heat than we will never get the accurate temperature.
Why do you think the heating apparatus was coiled? (wound in circles).
Maybe because it’s easily to make the liquid inside get heat.
Why do you think the vessel we held the water in was made of aluminium (Al) and not some other material.
It does not easily ignite,Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper.
If you had to pick another material to make the vessel out of what would it be? and why?
Maybe copper because it is a good thermal.
Would you expect the value we measure for the SHC of water be exactly 4200 J / kg / K? Justify your answer.
Yes but I can't remember the value we measure.
Because in our experiment, we want to find out, how long will it take if the temperature raises 10 degree. It’s about the heat, if it’s not insulated, that means you don’t have a layer of other materials inside it to protect from heat than we will never get the accurate temperature.
Why do you think the heating apparatus was coiled? (wound in circles).
Maybe because it’s easily to make the liquid inside get heat.
Why do you think the vessel we held the water in was made of aluminium (Al) and not some other material.
It does not easily ignite,Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper.
If you had to pick another material to make the vessel out of what would it be? and why?
Maybe copper because it is a good thermal.
Would you expect the value we measure for the SHC of water be exactly 4200 J / kg / K? Justify your answer.
Yes but I can't remember the value we measure.
scientific journal reflection
Title: Seed production and longevity, seasonal emergence and phenology of wild radish (Raphanus raphanistrum L.)
Author: TG Reeves, GR Code and CM Piggin
Summary:
This journal is about seed production, seed longevity, seasonal emergence and phenological development in wild radish and they found out temperature appeared to influence development up to flowering, but photoperiod affected the length of flowering.
Reflection:
About the language, it’s very different from novel, it’s much more academic. And about the structure it’s clearer. Not like the novel, author just write whatever they think and not care about the structure very much. But in the science journal it has steps and explain the detail very well so it has very clear structure. They communicate results by posting their results online. This text is very clear.
Author: TG Reeves, GR Code and CM Piggin
Summary:
This journal is about seed production, seed longevity, seasonal emergence and phenological development in wild radish and they found out temperature appeared to influence development up to flowering, but photoperiod affected the length of flowering.
Reflection:
About the language, it’s very different from novel, it’s much more academic. And about the structure it’s clearer. Not like the novel, author just write whatever they think and not care about the structure very much. But in the science journal it has steps and explain the detail very well so it has very clear structure. They communicate results by posting their results online. This text is very clear.
REFLECT UNIT 1
I used to think in the coffee experiment, in the same time the one with milk will have lower temperature, but now I know it's the black coffee will have the lower temperature.
I used don't understand why the milk one will cool slower but now I know that's because the milk is cold, put it in the coffee and make the coffee has lower temperature so the difference between the constant temperature of the surrounding is smaller. In the same time bigger difference will make the rate of cooling faster, too.
I used to think the earth is a sphere, but now I know it's a ellipsoid.
I used to think lab report is only about data and conclusion, but now I know there are 10 specific steps to make a lab report.
I used to think the most important part of physics is the conclusion, we don't need to care about how to get the conclusion, but now I know the experiment is the most important. It's not teacher gave us the knowledge any more, it's our term to discover the science by ourselves!
I used don't understand why the milk one will cool slower but now I know that's because the milk is cold, put it in the coffee and make the coffee has lower temperature so the difference between the constant temperature of the surrounding is smaller. In the same time bigger difference will make the rate of cooling faster, too.
I used to think the earth is a sphere, but now I know it's a ellipsoid.
I used to think lab report is only about data and conclusion, but now I know there are 10 specific steps to make a lab report.
I used to think the most important part of physics is the conclusion, we don't need to care about how to get the conclusion, but now I know the experiment is the most important. It's not teacher gave us the knowledge any more, it's our term to discover the science by ourselves!
8 essential science practice
SP 1--- REPRESENTATIONS & MODELS
--Use representations or models to represent scientific phenomena pr solve problems.
We learn how to model our experiment results in excel graph.
SP 2---CALCULATIONS
--use Mathematics and calculations appropriately.
About this part we calculated the circumference of the earth and calculated how long has one woman died as a detective.
SP 3---QUESTIONING
--Engage in scientific questioning to guide inquiry based investigations.
For all experiments, questioning is always the first part and the important part in the experiment.
SP 4---COLLECT DATA
--Plan and implement data collection strategies in relation to specific scientific questions.
Every time we put the collected data into table form to make it clear to see.
SP 5---ANALYZE
--Analyze and interpret evidence gathered from an investigation.
After collecting the data, analyze them and you will get a specific conclusion.
SP 6---JUSTIFY
--Justify and explain data results and analysis through debate and argumentation.
From the coffee experiment, we learn how to justify the data step by step.
SP 7---IDENTIFY ERRORS
--Find out the errors during experiment and find out what makes the result wrong.
Just like the coffee experiment, there is a mistake in our results. Our results say two kinds of coffee are the same but the truth is they are different so then we find out what did we do to make this error.
SP 7---CONNECT
--Connect concepts learned and discussed in class to society, technology and the environment.
After the coffee experiment and the mass experiment, we communicated our results and ideas with other groups.
--Use representations or models to represent scientific phenomena pr solve problems.
We learn how to model our experiment results in excel graph.
SP 2---CALCULATIONS
--use Mathematics and calculations appropriately.
About this part we calculated the circumference of the earth and calculated how long has one woman died as a detective.
SP 3---QUESTIONING
--Engage in scientific questioning to guide inquiry based investigations.
For all experiments, questioning is always the first part and the important part in the experiment.
SP 4---COLLECT DATA
--Plan and implement data collection strategies in relation to specific scientific questions.
Every time we put the collected data into table form to make it clear to see.
SP 5---ANALYZE
--Analyze and interpret evidence gathered from an investigation.
After collecting the data, analyze them and you will get a specific conclusion.
SP 6---JUSTIFY
--Justify and explain data results and analysis through debate and argumentation.
From the coffee experiment, we learn how to justify the data step by step.
SP 7---IDENTIFY ERRORS
--Find out the errors during experiment and find out what makes the result wrong.
Just like the coffee experiment, there is a mistake in our results. Our results say two kinds of coffee are the same but the truth is they are different so then we find out what did we do to make this error.
SP 7---CONNECT
--Connect concepts learned and discussed in class to society, technology and the environment.
After the coffee experiment and the mass experiment, we communicated our results and ideas with other groups.
calculating the circumference
1. I want to calculate two circumference of the earth and compare them are the same or not.
a. circumference= 39144. 24
b. circumference=41495. 625
it’s not the same so it’s not a perfect sphere.
Percent error=|41495.625-40075.7|/ 40075.7km×100% = 4%
2. equatorial=40075.7km 40075.7/100/24≈16.698
polar route=39900km 39900/100/24=16.625
polar route is quicker
a. circumference= 39144. 24
b. circumference=41495. 625
it’s not the same so it’s not a perfect sphere.
Percent error=|41495.625-40075.7|/ 40075.7km×100% = 4%
2. equatorial=40075.7km 40075.7/100/24≈16.698
polar route=39900km 39900/100/24=16.625
polar route is quicker