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Physics library
Course: Physics library > Unit 18
Lesson 1: Discovery of magnetismCompass interactions
If we float two identically magnetized needles they will always orient themselves in the same way. Why? Created by Brit Cruise.
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The needles are pointing in the same way because one needle is positively charged and the other one is negatively charged?(2 votes)
I think you are confusing "charge" with "magnetism". They are closely related, but they are not the same thing.
Notice that in both instances the point of one needle was attracted to the head of the other needle. It was a case of opposite poles attract.
Even though he does not show it on the video, can you deduce in which way the pins were magnetized?
a) Both rubbed in the same direction (rubbed from plastic ball to point), or
b) Rubbed in different directions (one needle was rubbed plastic ball to point, and the other was rubbed from point to the plastic ball)(15 votes)
about the MRI thing, would it still point North?(4 votes)
Not necessarily. The reason the needle points north is because the south pole of the magnetized needle is drawn to Earth's magnetic north pole. The water helps overcome friction. If the needle was sitting on rough concrete, the relatively weak magnetization of the needle wouldn't be strong enough to overcome the friction of the concrete. In other words, the south pole of the magnetized needle "wants" to get closer to Earth's magnetic north pole, but other forces, like friction, or you holding it in your hand in a different direction, might be stronger. If the compass was near a very strong magnet, like you'd find in an MRI machine, then the south pole of the magnetized needle would be drawn more strongly to the north pole of the MRI machine than to the north pole of Earth, and the north pole of the magnetized needle would be drawn approximately equally strongly to the south pole of the MRI machine... So, assuming the needle was across the room from the machine, it would simultaneously experience both of its ends being pulled toward the respective poles of the machine. That magnetism might be strong enough to pull the needle across the room to stick to the side of the machine, or if it was floating in water, (and the MRI's magnetism wasn't strong enough to pull the needle toward the machine,) the north and south attractive forces would be approximately equal, making it behave like the neutralized compass in the "Neutralize a compass" video.(1 vote)
why did the guy keep pushing the two north and south needles apart?(2 votes)
the two needles were attracted to each other. I believe he just wanted to make sure that the needles were behaving as they normally would and weren't somehow affecting each other or that the results were a fluke.(3 votes)
How is it possible if in a magnet similar poles retract, But in this video two identically magnetised needles attract?(1 vote)
Each magnet has a north pole and also a south pole. Therefore each magnetized needle has a north pole and also a south pole. Opposite magnetic poles attract. Therefore The north pole of one needle will attract the south pole of the other needle. Each of the needles attracts the other in this way. This is the same reason they align to Earth's magnetic field. you can even get them to attract each other in slightly different ways: v^, >>, << . The most likely orientation is N<<, where each needle points north and the needles are in contact.(5 votes)
- Why are they pointing in the same direction? Shouldn't they be pointing in opposite direction?(2 votes)
A famous saying: "Opposite Poles attract" I think you are confusing this with pole direction.
Meaning these experiments are shown to represents compasses; as in North and South.
So both being the same (magnetized) Think of two different compasses. The end points will be attracted to each other; however they will still behave as a normal compass. (Pointing in their original positions, North and South)(1 vote)
If we float two identically magnetized needles they will always orient themselves in the same way. Why?(2 votes)
The white bits are still just styrofoam?(1 vote)- Yes! though you can use anything that floats(2 votes)
- why are the magnetized needles trying to join together?(1 vote)
- The opposite sides are attracting each other. If you face one of the needles the other way, they would repel each other.(2 votes)
I think the magnetized needles will always orient themselves in the same way because each needle has a unique magnetic field and there is only one equilibrium position. Am I right?(1 vote)- if you watch the previous video, you'll see this isn't true. Brit magnetized one to point south and one to point north.(1 vote)
- how do they go together like that is it a trick.(1 vote)
- no, it's called magnetism. They go together for the same reason magnets go together.(1 vote)
Video transcript
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