Hypothetical physics

[ShadeZ]

If you could make your weight anything in an instants notice what would this result in? I have species that can modify their weight so they become faster or heavier as the situation requires. Modifying their weight is magical and doesn't affect their muscles, strength, or physical appearance.

 

[Chasejxyz]

Weight != mass

Weight (Newtons{kilogram/m/s^2) = mass (kilograms) x gravity ( m/s^2) Weight is the force acting on an object due to gravity. This is why your weight on Earth and your weight on the Moon aren't the same. There's even a Magic School Bus episode on this entire concept if you want to know more about it.

So when you say that you can make "your" "weight" changed, what exactly are you talking about? Are you changing your mass? Are they adding/removing neutrons or protons to their molecules? Are they just accumulating extra stuff? Where is that going? Changing molecules has huge impacts, like if you shove too many neutrons into something then it becomes unstable, and that's how you get radioactive decay! Which is not good for most living things.

Or are you changing the force of gravity in an area that just so happens to be the space your body is occupying? Because that has other, far-reaching implications that I am too dumb to do the math for.

 

[WooHooMan]

Well said, Chasejxyz, but I wouldn’t be so quick to dismiss the gravity manipulation angle. Mostly because that’s the only way I can see this working in a way that’s even slightly believable (in a fantasy context, that is).

I think you’d be better off saying “gravity magic makes this 150 pound guy seem to weigh 500 pounds” and leave it at that. I think trying to figure-out the real physics of this is way more trouble than it’s worth. I’d imagine that at the very least, a sudden change of weight like that would just immediately result in the person being crushed under their own weight.

 

[Rosemary Tea]

Is an explanation really necessary?

That premise could simply be magical realism. Kind of like this story by Stephen King, in which the MC mysteriously loses weight without his appearance changing at all. No explanation is ever given, it just happens.

In reality, apparent weight can change without actual weight changing. If you've ever had a pet or child fall asleep in your lap, you'll have noticed that they felt heavier once they were asleep. But their weight, as measured on a scale, would still have been the same.

The difference between dead weight and live weight is minuscule, but you could expand on that for fantasy purposes. Imagine a greater difference in weight that can be manipulated at will.

 

[Eduardo Ficaria]

Adding to all what has been said above, regardless of how that antigravity trick is achieved, you should be very careful of unexpected consequences ShadeZ . I say this because I remember a short story by Isaac Asimov in which one character kills another using an antigravity device in a very unexpected way, and the action was that the object being subjected to the antigravity field was effectively and instantaneously ejected from Earth at light speed while piercing cleanly through everything in its path, including the heart of the unsuspecting victim. The antigravity effect was complete, meaning that the field completely nullified all gravity, and that explained the ludicrous speed of the deadly object (a billiard ball).

So, what I imagine you want to give your species is some sort of "natural antigravity buoyancy", right? Well, you could take a look to animals like whales or sharks, or just fishes in general, and see how they achieve their buoyancy balance under water. Essentially it will be some organ or combination of them that gives them that skill. In your species' case, it could be an organ that requires some "magical" substance to make the antigravity trick possible. Now, if the species have evolved to have such organ, that means they are able to feed themselves with the required substance in their natural environment and that the organ gave them an evolutionary advantage. That, or the species is the creation of a mad scien... wizard.

 

[skip.knox]

I agree that no explanation is needed. In fact, explaining invites critiquing. The character can magically get heavier or lighter. OK. Then what? That's the interesting part, the then what part. (wow that last clause is strange)

I kick it back to the OP. What sort of consequences are you imagining? It's one of the rules of fantasy writing (which I invent on a whim): them as what invents the thing must invent the consequences.

 

[ShadeZ]

It is a side effect of paranormality. They simply shift weight its magical not scientific.

 

[WooHooMan]

I’ll echo what Slip said:

explaining invites critiquing

You’re likely better of just saying “they’re magically heavier” and leaving it there.

Although, I’ll maintain that if their strength is unaffected, an immediate increase in weight would probably just crush them.

 

[skip.knox]

Although, I’ll maintain that if their strength is unaffected, an immediate increase in weight would probably just crush them.

True. It's bound to distract at least some readers. It's worth asking, OP, why you want this in the first place. What role does it play in the story? Are there other strategies available? I can think, for example, that getting lighter might allow someone to fly. You could just as easily have them fly, without needing an underlying explanation.

Can you give some examples of how this ability would work in practice? In an actual scene?

 

[K.S. Crooks]

Perhaps instead of changing their weight or mass, they change their local gravitation. This would have the benefit of allowing them to levitate, jump from great heights, etc. No flight since this would require some type of propulsion.