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Bohr's model of hydrogen | so do we still not know that why do electrons not fall into the nucleus of the atom,i mean they are continuously emitting energy and of course at a point in time they should fall into the nucleus,what is the explantaion for that? | This is one of the main reasons we know that the Bohr model of the atom is wrong.
In the quantum model of the atom electrons in their lowest possible orbital are in their ground state and can't be in any lower energy state and they do not radiate energy. |
Bohr's model of hydrogen | Is Bohr's Model the most accurate model of atomic structure? | No, it is not. The quantum description of the electron orbitals is the best description we have. |
Right-hand rule | *How could we measure the force through the loop*?
Use a compass. In practise, wrap the wire around the compass and observe how strongly the needle aligns with the direction of the field. | That is how you make electromagnetisism. |
Force over distance | Force of magnet m= Strength of magnet M/Distance from the affected object
Is my equation correct? | In 3 dimensional space the strength of fields like magnetism and gravity decrease with the square of the distance so if you double the distance you decrease the strength by 4 times. |
Force over distance | Does anyone know why earths magnetic field went berserk at the exact same time the each WTC tower fell to the ground? | Do you have a citation for that? Sounds like BS to me. |
Force over distance | if there is a giant strong magnet bigger than the earth, will the earth move? | good question... I guess it would feel a force. But the magnetic field of the Earth is relatively weak. It is strong enough to change the direction of charged particle coming from the Sun and outer space but i think the force due to another big magnet would be fairly small.
Also, consider that the Sun also has magnet fields which are fairly strong.
Any thoughts?? |
What's next | Can you do an experiment that shows some of the topics from the physics videos about magnetism? | Yes I'm currently planning the next bath of videos. Is there something specific you are hoping to see? |
What's next | What does it mean when its says, "Multiple windings?" | A winding is several loops of wire, grouped together. In the video he made one winding comprised of seven loops. Most motors have several windings comprised of 10s to 100s of loops each, depending on the design of the motor.
When electric current passes through the wires of a winding, the winding produces a magnetic field which is attracted to one of the fixed magnets and repelled by the other. This is what causes the winding to rotate. By having more windings, a motor can be made more powerful. |
Lever | How is simple machine useful in lifting thing | Simple machines increase force, increase distance, and change direction |
Lever | Is there a relationship between the distance the load force moves and the distance the effort force moves? | Absolutely! He explains this in the mechanical advantage videos but more easily you can think of it like a wrench turning a stuck bolt. Just using the wrench doesn't work but if you put a pipe on the handle of the wrench to extend the handle, the bolt easily breaks loose. Why? Because the force you apply times the distance of the handle creates what we call a "moment" (a turning force) on the bolt. Mathematically expressed" F * d = P (where P is the moment) |
Lever | What materials do you use for this demonstration so that we can try a hands-on as well? Thanks! | Hi! You could use a ruler and a slim pencil rubber. The advantage of using a ruler is that you can literally measure the distances as you change the mechanism! And the rubber won't let the ruler slide apart, but remeber that it has to be slim, otherwise it won't represent a fulcrum. As for the weight, some coins will do the job. Hope you can do it yourself! Thank you! |
Lever | in the middle of the video how did he know to put on the coins | it was probably part of an experiment he had to demonstrate. |
Lever | in a lever just like the fulcrum was moved to different positions to equalise the position of load and effort... does situation comes where the load has to be moved towards the fulcrum to balance the lever arrangement,, if so can load be moved by keeping fulcrum intact? | yes in the 2nd class lever the load is near the fulcrum eg luggage bag |
Pulleys | what's the point of a fixed pulley if there's no mechanical advantage? | They can change the direction of a force not the actual speed. |
Pulleys | Whoo, first question ok! So looking at the figure in 2:28 in the Simple Machines video specifically, I'm intuitively confused about how we "lost" 50N of force/ only have to exert 50N to pull a 100N block? What happened to the other 50N? Who's pulling that part? Also, if we assume that both pulleys are massless, what is the force on the "bar" holding the fixed pulley, and the force (tension) and direction of force on string 1 and 2? | The 50N of force are not lost. When you pull with a 50N force to move a 100N block, it moves 1/2 the distance. The energy is conserved. |
Pulleys | This is really col but i don't know if I have all the stuff to make this,isn't there an easier way to make it. | why not take a tube like object (a desk lamps adjustable neck) that is suspended in mid air. take a string and tie it round a eraser and then put the string over the top. that way when you pull the non eraser end the eraser will rise up. just like a pulley! YAY! |
Pulleys | Please review, and correct my thoughts:
Video 1:
Q1. no mechanical advantage.
Q2. Can use this, so that instead of lifting something above your head (against gravity), you can push something else down and work with gravity.
Video 2:
Q1. No idea, but I can see the effects i.e. A heavy gondola on the right can easily be raised. A force downward on the left, causes a much larger upward force on the right.
Q2. The right gondola moves approximately half the distance of the one on the left.
Q3. Since the right gondola moves half the distance, it implies that it also requires double the force. Therefore, a force on the left applies about double that force to the right, indicating a mechanical advantage to the right gondola.
Video 3:
Q1. So that the left can apply a large force over a small distance causing the right to travel a large distance with a minimal force applied.
Q2. The gondola on the left travels much less distance, approximately 1/4 the distance travelled by the right gondola.
Q3. The gondola on the left requires more force, therefore, it has the mechanical advantage.
Motorized Pulley Video:
Q1. Didn't quite understand what was done to even it out.. I had my own idea, but it wasn't the technique used. My idea: Add an identical second motor and wheels on the right side, which would cause the weight to tilt to the right. Thus, the same force is applied on either side.
Q2. I need to understand question 1 first! - But thoughts: The pulley wheel on the right requires the most amount of force, therefore, it has the mechanical advantage? | Motorized Pulley Video:
The video's way was to connect the end of the string on the right side to the original motor so it reeled in the load from both ends, making it level.
The second question wasn't asking which pulley has mechanical advantage, but rather what the mechanical advantage was in terms of numbers. The "Simple Machines" video shows you how to calculate that. |
Pulleys | what is better for lifting heavy objects a pulley or a lever | Pulley pros:
1. Easy to transport (if you attatch a pulley system to a crane, for example)
2. Able to lift the object much higher
Cons:
1. Non-efficient for small tasks
2. Time-consuming to make
Lever pros:
1. Easy to make.
2. Object easily slides off the lever to destination
Cons:
1. It's almost impossible to push a lever and an object at the same time so it's not really great for transport.
2. Cannot lift objects straight (it will tilt to one side) so if you were carrying, say, a big basket of some sort with items inside, the items inside the basket could fall out due to the tilting.
3. Not great for lifting things off into the sky.
So to answer your question, it depends on what the situation is. Hope this helps! |
Pulleys | How is the mechanical advantage equal to the number of strings? | The tension in the string is the same throughout the pulley system. If you look at the the tension on the strings that are doing the lifting you will see that if there is 1 string there is 1 times the tension lifting but if you have 2 string you have twice the tension lifting so the lifting force it is directly proportional string tension times the number of strings. |
Experiment: What's the shape of a magnetic field? | If you turn on the switch to operate a lamp, and the lamp has no light bulb, does it consume any electricity? | No electricity is consumed, because there is no complete circuit enabling electricity to pass. |
Simple machines and how to use this tutorial | Technically there are only three simple machines, right? | No, there are 6 distinct simple machines. Pulley Screw, Wheel, Lever, Wedge, and Inclined plane. I really liked the explanations given at http://iqa.evergreenps.org/science/phy_science/ma.html
Mathematically a Wedge and Inclined plane are similar, but as far as application they are very different tools for different purposes. I'm also not sure which of the other 3 you think are the same but I can assure you there are 5 types of simple machines. |
Wheel | how can a jack wheel lift a car | Physically, the center of gravity for a car is right in the middle, but the jack has strong suspenders/ leverage that is can lift a car off the ground, moving the center of gravity not too much, but still sustainable to not break down, so you can lift the car! (Well, maybe only 1 side, but ok). |
Measure the Earth's field! | Is there a way to measure magnetivity? How would you measure something like that? | Yes, you can do it with Teslameter. It麓s relatively expensive apparatus or cheep (free) application on mobile. :-) |
Measure the Earth's field! | What are the materials that i can use to make a compass & one household magnet. | magnet that attract is northpole and sorthpole and the one that replling are northpole and northpole and sorthpole and sorthpole |
Measure the Earth's field! | i liked to play with magnets alot when i was little | so do i its because of the gravity on the earth! |