Basic Lashing problem

[FlashWrogan he/him]

So there was an event in the prologue, during the fight between Szeth and Gavilar that never made sense to me:

Szeth gathered himself, then leaped into the air, Lashing himself backward and to the right as the king arrived. He zipped out of the way of the king’s blow, then Lashed himself forward with two Basic Lashings in a row. Stormlight flashed out of him, clothing freezing, as he was pulled toward the king at twice the speed of a normal fall.

The king’s posture indicated surprise as Szeth lurched in midair, then spun toward him, swinging. He slammed his Blade into the king’s helm, then immediately Lashed himself to the ceiling and fell upward, slamming into the stone roof above.

So a basic lashing removes the objects attraction towards the planet and shifts that same attraction towards the indicated direction. A 200lb man that lashes himself to the ceiling now weighs -200lbs, or if a scale were attached to the ceiling upside down, he would weigh 200lbs. If he put two Basic Lashings on himself towards the ceiling, he would have twice the weight, and the scale on the ceiling would read 400lbs.

My issue with this scenario is the rate of fall. Per my understanding of physics, weight should have no bearing on the rate of fall. The only change we should see is the ability of other objects to affect his momentum, and the force with which he hits other objects. I'll provide an example from HoA (spoilers):

We see Sazed make himself lighter when descending the elevator shaft into the Inquisitor's home. The only reason that his rate of fall is slowed is because he is light enough for the wind resistance to slow him down. If he had tried the same thing in a vacuum, his weight would have changed nothing.

So why does Szeth fall twice as fast? Unless there is something I am missing in the way Basic Lashings or the physics of weight work, the only possibility I can find is that Brandon made an error here.

[lDanielHolm he/him]

You misunderstand the physics involved. He is not making himself weigh twice as much. He is making gravity pull twice as hard. Instead of being pulled towards Gavilar at 1 times Roshar gravity, he's pulled at double Roshar gravity.

Edited November 1, 2012 by lDanielHolm

[FlashWrogan he/him]

You misunderstand the physics involved. He is not making himself weigh twice as much. He is making gravity pull twice as hard. Instead of being pulled towards Gavilar at 1 times Roshar gravity, he's pulled at double Roshar gravity.

Isn't that the same thing though? Doubled gravity makes the objects weight doubled (but not their mass). An increased gravity pull or weight shouldn't affect the speed of descent.

[Pagerunner he/him]

Isn't that the same thing though? Doubled gravity makes the objects weight doubled (but not their mass). An increased gravity pull or weight shouldn't affect the speed of descent.

It all goes back to Newton's second law: Force equals Mass times Acceleration. Szeth is doubling up the 9.8 meters per second squared (acceleration) without changing his mass - a net doubling of force without changing his mass. Sazed would alter the effective force through changing his mass without changing the acceleration.

It's like how things fall slower on the moon, regardless of their mass, because the moon's acceleration is lower than earth's.

[FlashWrogan he/him]

It all goes back to Newton's second law: Force equals Mass times Acceleration. Szeth is doubling up the 9.8 meters per second squared (acceleration) without changing his mass - a net doubling of force without changing his mass. Sazed would alter the effective force through changing his mass without changing the acceleration.

It's like how things fall slower on the moon, regardless of their mass, because the moon's acceleration is lower than earth's.

So if I understand you correctly (the acceleration thing confused me a bit), Szeth didn't fall faster than he could have from one Basic Lashing, he simply hit that top speed in a smaller amount of time. So two people jump off of a cliff, one with the gravity pull equal to one Basic Lashing, the second with the gravity pull equal to two Basic Lashings. The second's rate of descent will increase faster but will hit top speed quicker than the first. The end result is that both end up descending at the same rate, but the second will hit the ground first since he hit the top speed first.

Do I understand this correctly?

[lDanielHolm he/him]

Isn't that the same thing though? Doubled gravity makes the objects weight doubled (but not their mass). An increased gravity pull or weight shouldn't affect the speed of descent.

You're looking at it from the wrong angle.

You calculate weight by multiplying an object's mass by the force of gravity. The force of gravity is measured in acceleration -- on Earth, that is 9.81 meters per second per second. Every second, a falling object within Earth's gravitational pull increases its speed by 9.81 meters per second--though only in a vacuum. In air, it falls at up to a maximum of its terminal velocity.

As Pagerunner says, this is Newton's second law of motion: force equals mass times acceleration.

Since we have an increased force without an increase in mass, the only thing that can change is the object's acceleration. Sazed would get the same net result--an increased force--by increasing his mass instead of his acceleration.

So if I understand you correctly (the acceleration thing confused me a bit), Szeth didn't fall faster than he could have from one Basic Lashing, he simply hit that top speed in a smaller amount of time. So two people jump off of a cliff, one with the gravity pull equal to one Basic Lashing, the second with the gravity pull equal to two Basic Lashings. The second's rate of descent will increase faster but will hit top speed quicker than the first. The end result is that both end up descending at the same rate, but the second will hit the ground first since he hit the top speed first.

Do I understand this correctly?

No, not at all. What you are speaking of here is terminal velocity -- the point at which an object's drag through a fluid (like normal air) is equal to the pull gravity has upon it, making further acceleration zero (and making the object's speed constant, i.e. the theoretical maximum speed). With increased gravity, you have a higher terminal velocity. (Or, as Pagerunner put it: on the moon, you have less.)

Edited November 1, 2012 by lDanielHolm

[name_here]

The reason gravitational acceleration is fixed is because force is proportional to mass, and acceleration is proportional to force and inversely proportional to mass. Here, the force is doubled and mass is held constant, so acceleration rises. Terminal velocity would also increase but not double, because terminal velocity is due to air resistance, which rises non-linearly with speed.

Edited November 1, 2012 by name_here

[FlashWrogan he/him]

Alright, I get it now. Thank you all for being patient with my physics illiteracy

[happyman he/him]

Actually, you hit on one of the subtle points of modern science, which is that gravitational mass (which determines the strength of the force of gravity) and inertial mass (which determines how quickly something responds to a force) are the same. At Newton's time, there was no a priori reason why this should be true. It's not true for any of the other forces, where the "charge" (which determines the strength of the force) is determined by other factors entirely.

Thus what Szeth does in this scene is to change the form of the law of gravity without changing his inertial mass. Apparently, with Feruchemy, when you change your mass, you change both inertial and gravitational mass at the same time. It's a subtle difference.