Homework: Due Friday Read p. 83-86. work p. 86#1-7
Last Wednesday Mr. F. was absent; classes worked on a review WS (get one here) and today I handed out an answer key to check your work. See me if you still have any questions.
Today in class we brainstormed ideas about friction - what we think we know or want to know - to help guide tomorrow and Wednesday's inquiry lab: Friction - basically each group (or individual) will pick out an independent variable and test its effect on frictional force. Most groups will probably use our force sensors to get quantitative results (results with numbers) as part of their data. Data collection will take place tomorrow and possibly part of Wednesday, and will be mixed with notes and demonstrations about friction, air resistance, and still some fun ones involving inertia and Newton's 2nd law. Our next topic will be momentum; it ties well with Newton's 2nd and 3rd laws well... F=ma meets action - reaction forces.
Monday, October 31, 2011
Monday, October 24, 2011
10-25 time for acceleration
Today we explored the effect that altering time for an object to accelerate has on the measured value of acceleration, the force involved, and the damage that results when time to accelerate is shortened.
We analyzed time for an object to move from 20 m/s to a stop in two situations: one where the object stopped in 0.02 seconds, and another where the object stopped in 0.5 seconds. Accelerations were 1000 m/s^2 vs 40 m/s^2, and the forces (assuming a 2kg object) were 2000N vs. 80N.
We discussed the importance of time to accelerate and relation to design in helmets, playgrounds, and cars: if your head hits the pavement and your brain accelerates to a stop in 1mm versus hitting a softer surface and accelerates over 1cm (10x farther), the time for impact will be 10X longer and the force experienced will be 10X less.
We demonstrated this idea by trying to throw eggs into a loose sheet. Very few were broken, most likely due to other causes, and the school was accidentally targeted by a few off-aim students. Luckily it was outside!
Tuesday and Wednesday we'll be exploring the concept of friction and learning about some new tools to measure (scales)
We analyzed time for an object to move from 20 m/s to a stop in two situations: one where the object stopped in 0.02 seconds, and another where the object stopped in 0.5 seconds. Accelerations were 1000 m/s^2 vs 40 m/s^2, and the forces (assuming a 2kg object) were 2000N vs. 80N.
We discussed the importance of time to accelerate and relation to design in helmets, playgrounds, and cars: if your head hits the pavement and your brain accelerates to a stop in 1mm versus hitting a softer surface and accelerates over 1cm (10x farther), the time for impact will be 10X longer and the force experienced will be 10X less.
We demonstrated this idea by trying to throw eggs into a loose sheet. Very few were broken, most likely due to other causes, and the school was accidentally targeted by a few off-aim students. Luckily it was outside!
Tuesday and Wednesday we'll be exploring the concept of friction and learning about some new tools to measure (scales)
Tuesday, October 18, 2011
10-18
hmwk: p.111#1-8.
Today we discussed why astronauts "float" - they ARE falling toward Earth, but as they fall, they're moving to the side so fast that the Earth's curved surface drops out beneath them (ORBIT!), and they continually accelerate around the Earth, constantly changing direction, forever. As long as they don't speed up or slow down, they will remain at the same altitude forever.
In reality the international space station does need to be boosted occasionally; it does encounter *some* friction from *some* atoms or molecules of air as it moves by, slowing it down, and decreasing its altitude.
Most satellites are higher in altitude, and many are geosynchronous; meaning they remain over one spot on the Earth's surface permanently. (this is achieved at a specific altitude and velocity). Your satellite dish may be "aimed" at the satellite just when it's installed and point at that satellite forever, and our GPS satellites must have a very predictable location relative to the Earth's surface in order to work.
On the same lines of thought, if the Earth were to stop revolving about the Sun, it would fall in to the Sun, accelerating like a brick falling out of the sky. When we get to more astronomy topics and math, we'll see how long it would take for the Earth to hit the Sun if this were to happen. A real example is that the Moon is speeding up, and as a result, it is getting farther from the Earth by about 3cm per year.
After the gravity - weight and orbit discussion, classes filled out note cards to use to keep equations and to use on any future test. I also explained the algebra triangle, and how you could use it as a tool to help if you are struggling with Algebra and equations in class. It will not be a tool that you can use on everything, and I won't give you the triangles for future equations. It will be up to you to use them appropriately if you want.
Today we discussed why astronauts "float" - they ARE falling toward Earth, but as they fall, they're moving to the side so fast that the Earth's curved surface drops out beneath them (ORBIT!), and they continually accelerate around the Earth, constantly changing direction, forever. As long as they don't speed up or slow down, they will remain at the same altitude forever.
In reality the international space station does need to be boosted occasionally; it does encounter *some* friction from *some* atoms or molecules of air as it moves by, slowing it down, and decreasing its altitude.
Most satellites are higher in altitude, and many are geosynchronous; meaning they remain over one spot on the Earth's surface permanently. (this is achieved at a specific altitude and velocity). Your satellite dish may be "aimed" at the satellite just when it's installed and point at that satellite forever, and our GPS satellites must have a very predictable location relative to the Earth's surface in order to work.
On the same lines of thought, if the Earth were to stop revolving about the Sun, it would fall in to the Sun, accelerating like a brick falling out of the sky. When we get to more astronomy topics and math, we'll see how long it would take for the Earth to hit the Sun if this were to happen. A real example is that the Moon is speeding up, and as a result, it is getting farther from the Earth by about 3cm per year.
After the gravity - weight and orbit discussion, classes filled out note cards to use to keep equations and to use on any future test. I also explained the algebra triangle, and how you could use it as a tool to help if you are struggling with Algebra and equations in class. It will not be a tool that you can use on everything, and I won't give you the triangles for future equations. It will be up to you to use them appropriately if you want.
Monday, October 17, 2011
Weightless astronauts????? HOW?
On Friday we worked with the air track (nearly frictionless) and experimented around with gliders to verify Newton's 2nd law, F = m * a
Today I went over homework problems, including the bonus (#3) and we found that astronauts in orbit around the Earth are experiencing about 90% the same gravitational field as we are. So the big question looms: WHY???!!!!??? do the videos of astronauts show them "floating" or appearing "weightless"????
If you can explain it (from your memory - not reading a printout from the Internet) tomorrow for class, you may receive some rare bonus points!
After the gravity problem/discussion we made motion maps using videos of last Friday's air track videos and verified that they were accelerating at different rates, almost exactly as F=ma predicts.
Homework (Due WED): p. 111 # 1-8
Today I went over homework problems, including the bonus (#3) and we found that astronauts in orbit around the Earth are experiencing about 90% the same gravitational field as we are. So the big question looms: WHY???!!!!??? do the videos of astronauts show them "floating" or appearing "weightless"????
If you can explain it (from your memory - not reading a printout from the Internet) tomorrow for class, you may receive some rare bonus points!
After the gravity problem/discussion we made motion maps using videos of last Friday's air track videos and verified that they were accelerating at different rates, almost exactly as F=ma predicts.
Homework (Due WED): p. 111 # 1-8
Thursday, October 13, 2011
10-13 you might want to read:
Today classes worked on review problems from notes or homework, and most students had a chance to see their test grades.... most were rough. If you struggled, you may re-take the test under these conditions:
-You can only do this for one test - I expect you to get things figured out before next time as far as studying and test format, difficulty, content, etc.
-The test you re-take will be different from the first test. Studying the correct answers will do little; figuring out WHY you got certain questions wrong/right WILL help you.
-I will average the scores of your two tests.
-You may not re-take a test during class time. After school or by appointment otherwise.
I think this is the most equitable solution if you were taken off guard by the exam, or if you feel you know the content better now (our current unit applies much of what we were studying last unit)
Announcements: #3 on Monday's homework is bonus. Not huge, but it is pretty open-ended, so I don't expect everyone to be able to do it. I will answer it on Monday in class.
Grades will not be exported until Monday. I plan on getting all lab journals that have been submitted added in to your grade by that time; if Mom and Dad see your rough test grade, hopefully you did well on your lab and won't end up dead by the time Quarter grades are out.
If you want the optional assignment to count for this quarter, get it to me by tomorrow. (Friday). You can still turn it in for points until Wednesday.
Remember, quarter grades are impermanent. Semester grades are. If you are struggling now, you have over 50% of the points left in the semester to make up your grade (finals, increasing work/test load/speed) so you can move your grade up. If you have a good grade, keep it up! Your permanent transcript that you apply to universities with will have your semester grades on it, not quarter grades.
-You can only do this for one test - I expect you to get things figured out before next time as far as studying and test format, difficulty, content, etc.
-The test you re-take will be different from the first test. Studying the correct answers will do little; figuring out WHY you got certain questions wrong/right WILL help you.
-I will average the scores of your two tests.
-You may not re-take a test during class time. After school or by appointment otherwise.
I think this is the most equitable solution if you were taken off guard by the exam, or if you feel you know the content better now (our current unit applies much of what we were studying last unit)
Announcements: #3 on Monday's homework is bonus. Not huge, but it is pretty open-ended, so I don't expect everyone to be able to do it. I will answer it on Monday in class.
Grades will not be exported until Monday. I plan on getting all lab journals that have been submitted added in to your grade by that time; if Mom and Dad see your rough test grade, hopefully you did well on your lab and won't end up dead by the time Quarter grades are out.
If you want the optional assignment to count for this quarter, get it to me by tomorrow. (Friday). You can still turn it in for points until Wednesday.
Remember, quarter grades are impermanent. Semester grades are. If you are struggling now, you have over 50% of the points left in the semester to make up your grade (finals, increasing work/test load/speed) so you can move your grade up. If you have a good grade, keep it up! Your permanent transcript that you apply to universities with will have your semester grades on it, not quarter grades.
Wednesday, October 12, 2011
10-12
Today we reviewed Newton's 1st and 2nd laws of motion and added a bit of understanding / depth with how F=m*a applies to mass, weight, and gravity. Notes were given according to this outline and we had some additional inertia demonstrations.
Tomorrow we'll spend some time looking over exams and right/wrong answers and any arguments for points, and try to quantify (verify with numbers) Newton's 2nd law (F=ma).
Maybe we'll get to a discussion on why I claim all objects on Earth are accelerated at -9.81 m/s/s due to gravity, and why mass doesn't make a difference.
Tomorrow we'll spend some time looking over exams and right/wrong answers and any arguments for points, and try to quantify (verify with numbers) Newton's 2nd law (F=ma).
Maybe we'll get to a discussion on why I claim all objects on Earth are accelerated at -9.81 m/s/s due to gravity, and why mass doesn't make a difference.
Monday, October 10, 2011
Optional Assignment #2: Forces in 1 D
https://docs.google.com/document/d/1m8lELfvP4wkGvWnWX1vAQ1kCcUs4C2ZNVd0jKHpl53s/edit?hl=en_US
Turn in no later than next Wednesday, the 19th. You may email it to me, type and print out, or just write answers on notebook paper and turn in.
Turn in no later than next Wednesday, the 19th. You may email it to me, type and print out, or just write answers on notebook paper and turn in.
10-10 Newton's1st/2nd laws
HMWK tonight (102/103) Today in class: Demonstration of shooting a monkey/bear, depending on the class :-) showing, once again, that gravity does not affect horizontal motion of an object, and that projectiles (things moving through the air) curve due to this effect.
Notes: Inertia and Newton's 2nd law (below)
Announcement: If you need a book (a real book), Seckman has given FHS back some of our texts they borrowed in the past. See Mr. F. for a text to check out.
Notes:
Newton's 1st Law (Inertia): An object in motion remains in motion, an object at rest remains at rest... UNTIL/UNLESS acted upon by a net force.
Definition: Inertia is: Resistance to Acceleration
remember, acceleration is any change in velocity, which may be resulting from a change in speed OR direction.
Inertia is based on mass. More mass --> more inertia!
Newton's 2nd law: An object's acceleration depends on 2 things: Net force acting on it AND its mass.
This one has an equation: Fnet = m * a (net force = mass * acceleration)
Units: mass (kg) acceleration (m/s^2) and force is (kg*m/s^2) or just N (Newton). (Newtons are a derived unit - short for kg*m/s^2)
Practice problem:
5N net force
2 kg mass
a = ?
How to solve: Fnet = m*a <-- divide both sides of this equation by "m" to get: Fnet/m = a.
Put in numbers and you get 5N / 2kg = a Simplify to 2.5 N/kg.
**But you say N/kg isn't acceleration? Sure it is! Substitute kg*m/s^2 in for N in the above answer, and you should see that kg are in the numerator and denominator; they cancel, leaving 2.5 m/s^2.
Some classes also asked questions and had answers worked out for tonight's homework.
Notes: Inertia and Newton's 2nd law (below)
Announcement: If you need a book (a real book), Seckman has given FHS back some of our texts they borrowed in the past. See Mr. F. for a text to check out.
Notes:
Newton's 1st Law (Inertia): An object in motion remains in motion, an object at rest remains at rest... UNTIL/UNLESS acted upon by a net force.
Definition: Inertia is: Resistance to Acceleration
remember, acceleration is any change in velocity, which may be resulting from a change in speed OR direction.
Inertia is based on mass. More mass --> more inertia!
Newton's 2nd law: An object's acceleration depends on 2 things: Net force acting on it AND its mass.
This one has an equation: Fnet = m * a (net force = mass * acceleration)
Units: mass (kg) acceleration (m/s^2) and force is (kg*m/s^2) or just N (Newton). (Newtons are a derived unit - short for kg*m/s^2)
Practice problem:
5N net force
2 kg mass
a = ?
How to solve: Fnet = m*a <-- divide both sides of this equation by "m" to get: Fnet/m = a.
Put in numbers and you get 5N / 2kg = a Simplify to 2.5 N/kg.
**But you say N/kg isn't acceleration? Sure it is! Substitute kg*m/s^2 in for N in the above answer, and you should see that kg are in the numerator and denominator; they cancel, leaving 2.5 m/s^2.
Some classes also asked questions and had answers worked out for tonight's homework.
Thursday, October 6, 2011
10-6 and 10-7
Today I apologized for the challenge laid down by last night's homework; hopefully today's lesson smoothed things out for everyone.
Today we: Simplified the value we'll be using for "g" in class from -9.81m/s/s to -10 m/s/s.
Drew a motion map using the -10m/s/s and representing the velocity every second of an object thrown vertically.
Reminded everyone that gravity only affects an object's vertical motion (no effect on horizontal).
Worked through homework problems after having different explanations (worked much better for most)
Picked up one more homework assignment: READ p. 98-103; work #1-3 on p. 102 and 1-4 ,6,7 on p. 103. DUE MONDAY
Tomorrow: (Fun) demonstrations that gravity only affects vertical motion (I will try to show you different examples than just the video that we moved frame-by-frame on Wednesday). Plus a chance to win $1 if your reflexes are fast enough, and the physics behind the challenge.
Want to practice? http://www.humanbenchmark.com/tests/reactiontime/index.php
Get below 0.2s on this and you might have a shot.
Today we: Simplified the value we'll be using for "g" in class from -9.81m/s/s to -10 m/s/s.
Drew a motion map using the -10m/s/s and representing the velocity every second of an object thrown vertically.
Reminded everyone that gravity only affects an object's vertical motion (no effect on horizontal).
Worked through homework problems after having different explanations (worked much better for most)
Picked up one more homework assignment: READ p. 98-103; work #1-3 on p. 102 and 1-4 ,6,7 on p. 103. DUE MONDAY
Tomorrow: (Fun) demonstrations that gravity only affects vertical motion (I will try to show you different examples than just the video that we moved frame-by-frame on Wednesday). Plus a chance to win $1 if your reflexes are fast enough, and the physics behind the challenge.
Want to practice? http://www.humanbenchmark.com/tests/reactiontime/index.php
Get below 0.2s on this and you might have a shot.
Wednesday, October 5, 2011
10-6 in class
Thursday we will: Turn in homework (slip of paper handed out Wednesday (see yesterday's post on blog)(finish motion maps for some classes)
Work some practice gravity - relationship problems
Go over answers to homework problems
Discuss the independence of vertical and horizontal motion: Gravity affects only the vertical (up and down) motion of an object.
Demonstrations: Penny shooting, ball shot, monkey shooting, and the ever-fun but rarely-lucrative: Win $1 from Mr. Freeman! (all deal with gravity's acceleration)
HMWK: READ 98-103. really, you should read it. it will give you a good background for what we discuss in class. Take your time, read it, and you will be better prepared for class discussion, labs, demonstrations, and tests. After doing the reading, work p. 102#1-3, and p. 103 #1-4, 6&7. Due Monday.
Work some practice gravity - relationship problems
Go over answers to homework problems
Discuss the independence of vertical and horizontal motion: Gravity affects only the vertical (up and down) motion of an object.
Demonstrations: Penny shooting, ball shot, monkey shooting, and the ever-fun but rarely-lucrative: Win $1 from Mr. Freeman! (all deal with gravity's acceleration)
HMWK: READ 98-103. really, you should read it. it will give you a good background for what we discuss in class. Take your time, read it, and you will be better prepared for class discussion, labs, demonstrations, and tests. After doing the reading, work p. 102#1-3, and p. 103 #1-4, 6&7. Due Monday.
Tuesday, October 4, 2011
10-5 In Class
Wednesday we will look at one of the many reasons objects may accelerate, the force of gravity. We'll start with notes on what we know and don't know about gravity, and some **really simple** applications of a gravity equation.
Then we'll jump to solving for the amount of gravitational acceleration. This one gets a bit tricky, but it comes out that all objects accelerate toward the Earth at the same rate. The proof of this will come with Newton's 2nd law (Friday/Monday maybe).
After some lab-exercises analyzing and solving for "g" which is known as acceleration due to gravity, we'll look at sample problems involving "g" in place of "a" and find out some cool answers to acceleration problems for objects accelerated by gravity.
Tomorrow's homework (due Thursday): Read p. 104-105, and solve the following:
Explain your answers OR show work.
1a. How long will it take a ball dropped from a height of 2m to reach the ground?
b. How fast will the ball be moving when it hits the ground?
2. A rock is thrown upward at 30 m/s (about 70 mph) by a FHS geology student. How fast will it be moving after: a. 2 seconds? b. 3 seconds? c. 4 seconds?
3a. A penny is dropped off a building. Find its velocity 2.5 seconds later.
b. At the same time, a second penny was pushed off by a broom, moving horizontally at 2 m/s. Draw a picture relating the motions of these two pennies during the first 2.5 seconds of their fall from the same height.
BONUS: If the FHS geology student catches the rock, how fast will it be going, and how long was the rock in the air?
A cool video to check out relating to in-class activities and discussion:
http://dsc.discovery.com/videos/mythbusters-dropped-vs-fired-bullet.html
Or just look up on youtube: Mythbusters dropped vs fired bullet
Then we'll jump to solving for the amount of gravitational acceleration. This one gets a bit tricky, but it comes out that all objects accelerate toward the Earth at the same rate. The proof of this will come with Newton's 2nd law (Friday/Monday maybe).
After some lab-exercises analyzing and solving for "g" which is known as acceleration due to gravity, we'll look at sample problems involving "g" in place of "a" and find out some cool answers to acceleration problems for objects accelerated by gravity.
Tomorrow's homework (due Thursday): Read p. 104-105, and solve the following:
Explain your answers OR show work.
1a. How long will it take a ball dropped from a height of 2m to reach the ground?
b. How fast will the ball be moving when it hits the ground?
2. A rock is thrown upward at 30 m/s (about 70 mph) by a FHS geology student. How fast will it be moving after: a. 2 seconds? b. 3 seconds? c. 4 seconds?
3a. A penny is dropped off a building. Find its velocity 2.5 seconds later.
b. At the same time, a second penny was pushed off by a broom, moving horizontally at 2 m/s. Draw a picture relating the motions of these two pennies during the first 2.5 seconds of their fall from the same height.
BONUS: If the FHS geology student catches the rock, how fast will it be going, and how long was the rock in the air?
A cool video to check out relating to in-class activities and discussion:
http://dsc.discovery.com/videos/mythbusters-dropped-vs-fired-bullet.html
Or just look up on youtube: Mythbusters dropped vs fired bullet
Monday, October 3, 2011
10-3 Exam tomorrow!
Today in class we took our common assessment and discussed correct answers (as a review). I'll tell you how our classes did versus the other Physical/Earth science classes later this week.
After the common assessment, we took a measurement of how much the Earth accelerated a basketball using the same position sensor as last week. Most classes found this value to be around 9-10 m/s/s. This number will become increasingly important this week.
STUDY!!!
After the common assessment, we took a measurement of how much the Earth accelerated a basketball using the same position sensor as last week. Most classes found this value to be around 9-10 m/s/s. This number will become increasingly important this week.
STUDY!!!
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