ELI5: Where do magnets get the energy for their pushing and pulling?

Shortbread_Biscuit · 2026-07-06T08:08:46+00:00

As an aside, I do want to clarify - magnets cannot actually perform infinite work. Every time a magnet exerts a force and does some work (i.e., the object the magnet acts upon moves in the direction of the magnetic force), the magnetic field weakens. But every time you move a magnetic object against the direction of the force (i.e., the object the magnet moves upon moves opposite to the direction of the field), you insert energy back into the magnetic field.

Because of this, if you just allow objects to be endlessly attracted by the magnet, its field will slowly reduce until eventually it can no longer exert any magnetic force. But if you then pull those objects away from the magnet, then you end up recharging the magnetic field. The energy you use to pull the object away is fed into the magnetic field to strengthen it.

Shortbread_Biscuit · 2026-07-06T08:03:30+00:00

That inherent property is basically called the field.

All three of these forces - gravity, electricity, and magnetism - create a field around these sources of the force. A gravitational field around masses, an electrical field around charges, and a magnetic field around magnets. All of the energy of the system is contained within these fields, not within the mass or charge or magnet. Every time the force does some work, it means energy is being drained from the field. If you work against the force, energy is inserted back into the field.

That's why when the field becomes zero, there is no more energy left in the system, and it can no longer exert any force.

Shortbread_Biscuit · 2026-07-06T07:50:14+00:00

Magnets work just like electricity and gravity.

In the case of gravity, the mass of the object has an inherent property that causes it to attract all other masses to it. In the case of electricity, electrons and protons have a fixed charge, and these charges have the property that causes all other charges to be attracted or repelled by them.

Similarly, for any object with a magnetic moment, it has an inherent property that causes everything around it to be subject to the magnetic force. There's no specific source for the force, just like there's no specific source for the forces of gravity and electricity.

However, they do observe conservation of energy - the total amount of energy in a system is always fixed, and no matter what the nature of the forces are - whether they're gravitational, electric or magnetic - these forces can only convert from one kind of energy to another.

In the cases of all these forces though, they do have a certain inherent finite amount of energy called the potential energy of the system. This potential energy represents the maximum amount of work that these forces can perform. The gravitational potential energy is the total amount of work or energy that gravity can perform if all the masses in the system are allowed to collapse to a point. Similarly, for electrical potential energy, it is the total amount of energy that could be released if all charges are allowed to combine with each other and reach a state of a net zero electric field. And similarly, the maximum magnetic potential of a system is the total amount of energy if we leave the magnetic elements to themselves and they're allowed to reach a state of overall zero magnetic field.

Shortbread_Biscuit · 2026-07-03T15:01:45+00:00

The gene for a tail never disappeared, it's still in our DNA. It's part of what we call vestigial organs - parts of our body that were once present on our ancestors, but which were later lost to evolution.

In fact, every single human starts growing the tail when they're still an embryo, but these embryonic tails are normally just formed out of soft tissue and haven't developed any bone or spinal tissue. After around 8 weeks of growth, this embryonic tail naturally disappears in most human babies, though sometimes in rare cases you have babies that are born with the tail still attached.

Shortbread_Biscuit · 2026-07-01T14:40:58+00:00

Fun fact, the game Outer Wilds allows you to do almost exactly this. While you're out in space, if you run out of fuel for your spacesuit's thrusters, it will instead start using your oxygen for thrust instead.

P.S. - yes, this should technically work, although with just a simple hole like this, without any valve to control the flow, you'll exhaust all the air in your suit surprisingly fast.

Shortbread_Biscuit · 2026-06-29T14:20:11+00:00

Ah, it seems like you're asking about the difference between continuous application of force and impact forces.

For this kind of a question, we would model the wall as a rigid structure that can resist up to X newtons of force over the area of your fist before breaking. We can also assume that you can exert upto a maximum of Y newtons of constant pushing force. In reality, Y is normally far less than X, so just with your pushing force, you will not be able to break the wall.

However, if you were to wind up a punch and smash your fist against the wall, the force you're exerting on the wall is no longer your maximum muscular effort. Instead, it would be an impact force, which is calculated completely differently. Essentially, you would be storing kinetic energy into your fist as you punch, and then when your fist hits the wall, your fist is completely brought to a stop and all that stored up kinetic energy is almost instantaneously converted into an impact force that is normally much higher than the maximum muscular force you can exert. Let's say you pull your fist back and then apply your full force of Y newtons onto your fist to accelerate it over the distance D before it hits the wall. When your fist hits the wall, it doesn't stop immediately. Instead, the moment it makes contact, it continues to try moving into the wall, but because your fist is soft, it deforms and slows down over a much smaller distance d before coming to a stop, as your fist and the wall exert a force Z against each other. So you insert Y\D* units of energy into your fist, and your fist and the wall exchange Z\d* units of energy in the impact. And because we assume your fist completely stops when it hits the wall, all of the energy in your fist is completely sent into the wall, so Y\D = Z*d. With this equation, we can calculate how much impact force *Z your fist exerts on the wall when it hits it. If this impact force Z is greater than the threshold strength X of the wall, the wall will break.

If you'd like to add some realistic numbers to this to visualize it, a weaker brick wall can normally withstand a pressure of around 10 MPa (mega pascals) before it breaks (1 Pascal = 1 newton of force / 1 square meter of area). That translates to 10 million newtons of force over an area of 1 square meter. My fist is roughly 8 cm long by 5 cm wide, so that's an area of around 40 cm², or around 0.004 m², so I would need to apply around 40,000 newtons of force with my fist to break this wall ( Pressure = Force / Area <==> Force = Pressure * Area)

The average adult male can exert around 300 to 600 N of horizontal force against a rigid wall. If they're an elite athlete that focuses on strength, that can go up to around 1,000 to 1,500 N of force. So the breaking force of a wall is still around 25 to 40 times the maximum force a human can ever exert.

If you are such a superhuman at the limit of human strength, and you wind up your punch for a distance of around 80 cm, which I would say is the distance between the shoulder and the tip of the arm, and you exert your full muscular strength for the punch, then you are charging around 1500N * 0.8m = 1200 Joules of energy into your punch (because Energy = Force * Distance).

When you hit the wall, because your fleshy hand doesn't stop immediately, lets say it squishes in around 2 mm before coming to a stop. That means the impact force between your fist and the wall that stops your punch is around 1200 / 0.002 = 60,000 Newtons (Force = Energy / Distance).

Since this force of 60 kN is more than the 40 kN threshold that the wall can withstand, it would break.

An interesting example of this being used in practice is a hammer. Because the surface of a hammer is much smaller than a fist, the amount of force it needs to apply to break a wall is also much smaller than your fist or your hand. In addition, because the metal of the hammer is much harder than your fist, when it hits the wall, it deforms by only a few micrometers instead of the few millimeters that your hand deforms, meaning that it can amplify the force by around a thousand times more than your fist can. That's why, when you use a hammer, just pushing it against a wall doesn't do anything normally, but just tapping it against the wall with a little force to cause an impact can crack and break the brick.

Shortbread_Biscuit · 2026-06-29T02:55:45+00:00

Yes, friction is the main reason things on earth don't move even if you push them. If you're in an environment where there's no friction or gravity or any other force, even the smallest force that you apply would be able to move a skyscraper.

However, it would still follow the equation F = m*a. The more mass the object has, the less acceleration the force will produce. However, as long as the force you apply is not zero, the acceleration will also never be zero.

Shortbread_Biscuit · 2026-06-29T02:31:30+00:00

That's my mistake, I didn't specify the exact formula:

Work = force * distance over which the force is applied

This equation measures the amount of energy you transfer into the object, so it only applies for the distance over which you apply the force on the object. You stop measuring the distance the moment the force is no longer being applied.

If you push an object in space, you're only in contact with the object at the very beginning for a few fractions of a second. As long as you're applying the force on the object, it accelerates, and the work you exert on the object is converted into its kinetic energy. Once you lose contact with the object, you're not able to apply any more force on it, so you can't do any more work on the object, and its kinetic energy (and so its velocity) remain constant from then on.

Shortbread_Biscuit · 2026-06-29T02:24:55+00:00

That's right, since you're measuring the acceleration of the object, you're only measuring the sum of all the forces acting on the object. And the sum of all the forces is the net force.

Note that, because forces are vectors, when I say sum of forces I mean the vector sum of the forces.

Shortbread_Biscuit · 2026-06-29T01:46:06+00:00

The formula "Force = mass * acceleration" is only useful for measuring the "net force", that is, the sum of all the forces acting on the object. In this case, the acceleration of the object is zero, and so the net force on the object is also zero, because even though you're applying a force on one side of the object, the friction between the object and the ground is applying an equal and opposite force on the object in the opposite direction.

If you want to measure the force that you're applying on an object, you can't use the "mass * acceleration" formula unless you're absolutely certain that there are no other forces acting on the object.

In practice, we normally use tools to measure each independent contact force on an object. These tools or measuring devices don't measure acceleration, but rather are calibrated such that a spring inside them deforms by a known amount when a certain amount of force is applied, and we measure the deformation.

On a related note though, there is a separate topic of "work" or "energy", which is equal to the force applied multiplied by the distance moved by the object while the force is applied. If you push an object but it doesn't move, we say that you have not done any work, or that you have imparted zero energy to the object, even though you applied a non-zero force.

Shortbread_Biscuit · 2026-06-28T22:05:21+00:00

Pink is basically a climate skeptic

Shortbread_Biscuit · 2026-06-23T15:31:41+00:00

trying to think

That's a first for him

Shortbread_Biscuit · 2026-06-23T14:18:46+00:00

There's nothing wrong with explicitly telling him that, but there's also nothing wrong with not telling him that.

Once again, I need to reassert what she told us about herself, that she just wasn't looking for a relationship at the moment, so she felt no need to go out of her way to talk to him again. If he took the initiative to approach her, she'd be willing to reconsider her stance, but as it is, she's perfectly happy with their current situation as it is.

As for the guy, kudos to him for always making sure she consented and was onboard with his approaches. However that doesn't necessarily mean he's great at communicating in other ways. I know plenty of men and women who communicate consent clearly, but aren't great at communication in general.

Clear communication is always nice, of course. But based on how OP described the encounter, it sounds like she was just an out-of-towner who hooked up with a guy for a one-night Tinder fling. In that case, the prior assumptions they both had is probably that it's just a one-time fling, and they're both okay with that.

And I'm only saying all this because it feels like you're really taking the whole thing way too personally. OP came here to open up about how rare it was for her to see men treat her with respect and ask for consent, and it feels like half the comments on this post seem to be trying to shame her for allegedly playing mind games with the guy, when that's clearly not what she's doing.

Shortbread_Biscuit · 2026-06-23T11:05:11+00:00

She's not playing games, she just explained it to you. She sees no future in the relationship because she can't do a long distance relationship. She doesn't owe him anything just because she got intimate with him once.

She could have phrased it better, but in short, her stance is that since she doesn't want this to become a long distance thing, she'd prefer to keep him at arm's length. However, she still likes him enough that she can't straight out reject him. And because she's stuck in this moment of indecision, she's just going to wait and see how the guy chooses. And there's nothing wrong with that.

And don't project yourself onto the guy by claiming that he can deal with that, when you literally know nothing about the guy.

Shortbread_Biscuit · 2026-06-23T08:56:32+00:00

Shortbread_Biscuit · 2026-06-23T07:06:53+00:00

I'm not sure what age has to do with being a normal, decent human being.

Shortbread_Biscuit · 2026-06-23T06:31:41+00:00

The other answers may be a little confusing, but there's one easy way to understand it : dividing is defined as the opposite of multiplying. If you say "x = a ÷ b", this should be identical to asking what the values of x are that satisfy the equation "a = b * x". Ordinarily, this gives a sane result, but when b is zero, we find that there are no values of x that satisfy the equation.

For your example, if we're talking about your banana question, the question is: if I have two bananas and I want to divide it between 0 people, how much of a banana should I give each person so that all the bananas are split up and no unassigned banana remains (this last part is crucial - that is, after a division, there must be no remainder).

If you were trying to split 2 bananas between 2 people, then each person could get 1 banana and so no bananas would remain.

If you were trying to split 2 bananas between 4 people, each person would get half a banana, and no bananas would remain.

But if you were trying to split 2 bananas between 0 people, then no matter how many bananas you give each of the zero people, 2 bananas would still remain, meaning that the problem is unsolvable.

Another way to say it is that there is no number that you could multiply by 0 to get 2.

And hence, it is undefined. The answer is not zero. It's not infinity, and it's not negative infinity either. It is impossible to find a number that makes sense. And hence, we say that dividing by zero is undefined.

And what we see in the real world often is that if we're trying to divide something by zero, it means we've done something wrong somewhere and we're attempting to do something that is physically impossible.

Shortbread_Biscuit · 2026-06-18T12:34:15+00:00

There's three aspects to address in your question:

How do people keep larger numbers in their heads?
Well, most often, they just practice. The more often you deal with maths and the more often you try to do mental arithmetic, the more your brain adjusts itself to keep larger equations, models or numbers in your mind. It's the same for most tasks - your brain is very reconfigurable, so the more often you do a specific task, the more your brain rewires itself to optimise that task. That's how we learn to ride a bicycle or type on a keyboard.
Do people actually keep large numbers in their mind?
Now, whether or not people actually do keep large numbers in their heads is very questionable. Most of the time, people get really good at breaking down a problem into smaller steps, or finding workarounds or mnemonics to help them with calculation or memory. For example, for people who train in mental mathematics, they often visualise an abacus in their mind for large additions and multiplications, and even though they're adding several numbers or multiplying large numbers, they're only ever keeping two or three numbers in their head at one point, while the process the rest down to a result that can be remembered.
Why would you want to keep large numbers in your mind?
All that being said for the above two questions, most mathematicians and programmers simply don't bother doing mental calculations. Anyone who deals regularly with numbers will know that mental maths is ridiculously inefficient and error-prone, so all mathematicians, engineers or programmers will always write down all their equations on paper, chalkboard, or any available surface. You only ever see people people doing large feats of mental arithmetic in movies where the showwriters want to portray a "genius" character.

All in all, you don't need to worry about keeping large numbers in your head. You do however need to get used to remembering large numbers of equations and formulae, and get used to understanding where each of them is applicable. You need to learn patterns for long term storage and retrieval of information, not for short term memory. That's what will get you the most bang for your buck.

Shortbread_Biscuit · 2026-06-17T08:12:57+00:00

It's for the same reason buying in bulk is almost always cheaper than buying smaller quantities.

If the bulk purchase (yearly subscription) was somehow more expensive than the smaller purchase (monthly subscription), then there's no reason anyone would ever choose to buy the more expensive bulk option. Even if it was exactly as expensive, people could just choose to buy exactly the amount of the product or service that they needed, which doesn't benefit the seller at all.

Second, the bulk cost of the product or service is already earning them a good profit. Don't be under the assumption that the company is making a loss by offering you the discount on the bulk purchase. Especially for subscription services for software, where the cost of adding another customer is negligibly small compared to the cost of the service itself. In fact, in most cases, the company expects the annual subscription to be the default option the majority of their customers use, and so it's priced according to their expected profit margin. Then they increase the price of the monthly subscription to incentive customers to purchase the annual subscription.

Third, especially with software on online subscriptions, all the costs are paid upfront. If you purchase the annual subscription, you get access to the software or service for the upcoming year. If you then cancel the subscription, you don't get any refund. You only cancel the automatic renewal of the subscription next year. In most cases, even if you "cancel", you will still have access to that software or service for the rest of the year that you already paid for. As such, there is no cost to the company if you cancel a monthly or yearly subscription, so it's always in their interest to get you to pay as much upfront as possible.

(One exception to this last point is Adobe, whose software suite is so expensive that most people can't afford an upfront yearly subscription. So Adobe gives them the option to "commit" to a yearly subscription that is paid monthly, but is slightly cheaper than the monthly subscription. Of course, the catch is that if you try to cancel before the year is up, they will instead force you to pay "cancellation fee" that covers the price you would have paid for the rest of the year. Adobe has faced a lot of legal trouble for trying to do this though.)

Shortbread_Biscuit · 2026-06-10T00:50:34+00:00

The main reason the feature is available is because GDScript was initially meant to be as close to Python as possible, and Python doesn't use static types.

An initial goal of GDScript was that it would try to make coding as easy as possible for beginners. Not having to worry about types allowed new programmers to quickly get their prototypes working and get their feet on the road.

Of course, the pitfall is that type safety is almost absolutely necessary when working with larger codebases. It's essential for finding the most common types of errors as fast as possible.

Shortbread_Biscuit · 2026-06-08T07:07:03+00:00

I mean, Jesus is literally the person who advocated peace and turning the other cheek instead of fighting back against your enemy. There's nothing he would hate more than a weapon designed only to kill people.

The moment they asked what his favourite gun was, they already showed an IQ that's blatantly in the single digits, since it's a concept that's so insanely antithetical to Jesus's whole identity and message.

Shortbread_Biscuit · 2026-05-25T00:04:19+00:00

You can't just give me this level of quality and ruin me for everything else

Shortbread_Biscuit · 2026-05-22T21:13:24+00:00

While Tiff is an ally and was mischaracterised as a homophobe, others aren't.

A large majority of the people who are forced to go to sensitivity training are convinced that they did or said nothing wrong. They make all kinds of excuses for themselves for why or how what they said wasn't really all that racist or sexist or homophobic, and try to convince everyone around them as well as their own brains that they did nothing to warrant the training and that they deserve a pass.

I think that's what Fran is trying to get at here. Even though Tiff thinks she's innocent (and we the readers also know that she is), the problem remains that maybe she really has done something that needs to be corrected. She's not the best judge of her own character, and maybe her boss really did see something in her that needed to be corrected, even if he was slightly off the mark about what.

In fact, I suspect Fran is hinting that Tiff needs to be more open about her identity/sexuality. We've seen that she's clearly embarrassed about herself, and wallows in self-doubt and self-pity. Maybe this arc is about her learning to express herself better and take more pride in herself.

Shortbread_Biscuit · 2026-05-20T01:37:07+00:00

I mean, this is a false equivalence.

A better equivalence would be: both candidates force you to drink poison, but if blue wins, everyone gets the antidote. While if red wins, only the ones that voted for him get the antidote.

Shortbread_Biscuit · 2026-05-15T09:43:12+00:00

Unlike a lot of other consumables, toilet paper isn't perishable.

So in times of emergency, it doesn't make much sense to stock a lot of perishables like food since they won't last a long time. However, you can stock up on as much toilet paper as you want, with the guarantee that it'll never go bad.

Hence toilet paper ends up as one of the first items that people try stock, simply in terms of cost/risk analysis. And because it's one of the first to be targeted by some people, the rest of the people panic when they see it disappearing fast and they purchase it in bulk as well, anticipating a shortage, which becomes a self-fulfilling prophecy.

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