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Science questions
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dullard
Elite Member
That is the key to this thread. Far to many teachers/professors teach their students to parrot back phrases. Yet the students don't actually know what the phrase means or how to apply it. The recent push towards more standardized testing to see if students can parrot back phrases scares me. Yes, they can score quite well yet not know a thing. That means the test is worse than worthless, it is actually misleading.
I assume you don't test your students on their ability to parrot, DrPizza.
GeneValgene
Diamond Member
lol
DingDingDao
Diamond Member
Newton was short for Newtonius Appletius, quite a common name in Greek times.
😛
I think people get confused a lot with basic physics and newtonian "forces" becase they think of forces differently, like when I push on something, I am somehow creating the force out my my will to do so.
In reality, it's fairly complicated how your body moves. You are a complex system of muscles which are basically pulleys and counterpulleys rotating; the math for this is somewhat complicated. And any force you exert on an outside force comes from some other counterforce. If you are standing, pusing on a door, the force you push on the door and the force you exert on the ground, both downward and outward, are equal. The force doesn't last that long, a change of momentum occurs, and the door opens. But momentum is always conserved.
If you are floating in a vacuum, I like to say you still have "internal" forces. Which means you can reconfigure your body by one part forcing another part to do something. Like if you drop a cat which is falling and has nothing to push against, it can re-contort it's body to rotate so it lands on it's feet. Or if you are executing a super flying kick, you can kick 3 times before landing if you have the stomach strength and proper technique. Often, when kicking someone, newton's third law helps you rechamber your kick and kick them again, cuz each kick pushes back on you. But if you jump-kick someone, both of you will likely be bounced back so a second kick is out of range. Which is why it's better to keep one foot on the ground when you kick, you have more grip and can sustain the force longer.
I could write a book on the physics of a martial art. I think it's interesting stuff. A lot of the very detailed techniques are done by tradition but can be improved with a little knowledge of mechanics.
In reality, it's fairly complicated how your body moves. You are a complex system of muscles which are basically pulleys and counterpulleys rotating; the math for this is somewhat complicated. And any force you exert on an outside force comes from some other counterforce. If you are standing, pusing on a door, the force you push on the door and the force you exert on the ground, both downward and outward, are equal. The force doesn't last that long, a change of momentum occurs, and the door opens. But momentum is always conserved.
If you are floating in a vacuum, I like to say you still have "internal" forces. Which means you can reconfigure your body by one part forcing another part to do something. Like if you drop a cat which is falling and has nothing to push against, it can re-contort it's body to rotate so it lands on it's feet. Or if you are executing a super flying kick, you can kick 3 times before landing if you have the stomach strength and proper technique. Often, when kicking someone, newton's third law helps you rechamber your kick and kick them again, cuz each kick pushes back on you. But if you jump-kick someone, both of you will likely be bounced back so a second kick is out of range. Which is why it's better to keep one foot on the ground when you kick, you have more grip and can sustain the force longer.
I could write a book on the physics of a martial art. I think it's interesting stuff. A lot of the very detailed techniques are done by tradition but can be improved with a little knowledge of mechanics.
GeneValgene
Diamond Member
haha you are mistaking latin with greek
DingDingDao
Diamond Member
lol I know, just part of the joke 😛
Kyteland
Diamond Member
Funny thing is that Newton probably had a Latin handle he went by. Most written scientific discussion back then was in Latin, because that was the only language most of the scientists had in common. There's a few scientists better known by the handles they signed their letters with than their real names. :laugh:
DrPizza
Administrator Elite Member Goat Whisperer
I just had a fairly thorough questionaire that I had to fill out for the state based on the math curriculum. They kept asking questions related to "deep understanding of mathematics" and then asked questions about "achievement." I ended up skipping over a large section of responses and simply put down "Achievement on the exam does not indicate a deep understanding of mathematics. For the average and better than average students, I teach them for understanding. For below average students, I teach them how to be successful on the exam. Because of the amount of curriculum which must be covered, there simply isn't enough time to build up an understanding in students who have been assessed to be performing on the 5th grade level in mathematics. I cannot spend 2 classes explaining "why" you invert and multiply when you divide rational expressions. But, I can teach them "HOW" to do it. However, if you look at my exam results, even these students show "achievement" on the state exam."
the "understanding" part is where the parents must step in if the are capable. I don't worry so much about the correct answer when helping out my kids, I want to know the rational. We try to break homework down into simple visualizations that they are familiar with and it seems to work well.
ed21x
Diamond Member
they are not exerting equal force against one another. Force is a product of mass, but the third answer just sounds more scientific, and that is why everyone is picking it. in a free body diagram, the arrows would be pushing against one another, and the arrow with greater numbers would win out.
DrPizza
Administrator Elite Member Goat Whisperer
No,
In a free body diagram, you would have to include their forces against the ground.
If you get two bathroom scales, sandwiched back to back, and put them between the two players, you will see that it is impossible for one to push harder against the scales than the other. Both scales will always read the same amount. I spent 1 1/2 class periods with kids pushing each other all over the place, up and down the hallway, some sitting in chairs with wheels (computer chairs) and being pushed... Every time, both scales read the same amount.
In your free body diagram, draw a box (or point) for the smaller player. Include these 4 forces: normal force, frictional force against the ground (from sliding), gravitational force, and force against the player from the bigger player. Net force will be backwards for the smaller player. That doesn't mean that the two forces in question aren't equal. The force the little player is exerting on the big player *is not acting on the little player*. Therefore, it's not included in the free body diagram for the little player.
If you draw a free body diagram for the system of both players, then the force between them is not included. The only relevant forces (ignoring the normal and gravitational forces) are how hard the big player is pushing against the ground with his feet, and how hard the little player is pushing against the ground in the opposite direction.
Or
Think of it this way: The field that they're standing on is a sheet of ice. The little player is wearing some sort of cleats that grip the ice really well. The big player is wearing really really slippery shoes. The little player is going to push the big player backwards. Are you going to try to say that it's because suddenly the big player can't push as hard? The forces they exert on each other are equal. The net force on the big player is backwards, because he can't push against the ice. The net force on the little player is forward, because he CAN push against the ice.
DrPizza
Administrator Elite Member Goat Whisperer
ed21x, I see where your misunderstanding is. Balanced forces are not the same as equal and opposite forces.
Forces ALWAYS exist in pairs. And, the pairs are always equal and opposite.
Look at this diagram:
personA|object|personB
Each person pushes against the object with a force of 20 Newtons.
There is no net force on the object, therefore the object remains stationary (or remains moving at a constant velocity)
The equal and opposite forces are person A is pushing on the object with the same magnitude as the object is pushing on person A
Likewise between the object and person B.
Forces ALWAYS exist in pairs. And, the pairs are always equal and opposite.
Look at this diagram:
personA|object|personB
Each person pushes against the object with a force of 20 Newtons.
There is no net force on the object, therefore the object remains stationary (or remains moving at a constant velocity)
The equal and opposite forces are person A is pushing on the object with the same magnitude as the object is pushing on person A
Likewise between the object and person B.
DrPizza
Administrator Elite Member Goat Whisperer
Wow, if you think about it, it's almost scary that somewhere around 10% of the people are incorrect in regard to what a pen will do on the moon. 10% don't know about gravity??
I have a much better quality of this video that I use in class, but here:
http://www.bu.edu/core/cc105/lectures/L...anPhysics/images/featherdrop_sound.mov
I have a much better quality of this video that I use in class, but here:
http://www.bu.edu/core/cc105/lectures/L...anPhysics/images/featherdrop_sound.mov
littleprince
Golden Member
Interesting video. Never seen that. Too bad that woulnd't work on Earth as the air resistance would certainly inhibit the feather from falling.
The wording is a bit weird, but whatever, any Univ Physics/math prof should get it.
A liberal arts prof though, ah, who cares...
The wording is a bit weird, but whatever, any Univ Physics/math prof should get it.
A liberal arts prof though, ah, who cares...
LongCoolMother
Diamond Member
yay, got them all right. Taking Physics C AP in high school right now.
myusername
Diamond Member
Actually, friction would play little role. I think you were looking for inertia 😉
Kadarin
Lifer
The correct answer is that the only force that's really exerted here is God's Will. The pen falls because the Intelligent Designer wills it. The Volkswagon isn't exerting any force, but rather, the it is God's Will that the SUV move slowly.
All science is an illusion, a mode of thinking specifically designed to seperate people from their faith in God.
All science is an illusion, a mode of thinking specifically designed to seperate people from their faith in God.
DrPizza
Administrator Elite Member Goat Whisperer
*sigh*
Science education has failed this one. No, I wasn't looking for inertia (which for all intents and purposes means the same thing as mass). I was talking about forces, and Newton's 3rd law states... (drum roll...) they are equal and opposite.
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