Lifting strength formula for spinning a spear at high speed

[Breadbear83]

I found some feat of a character Spinning a spear at supersonic+ speeds, the spinning of the spear would already gives decent KE results, can lifting strength be applied to it? If so with what formula?

From the dimensions of the spears, if it were made of steel (7.9g cm³) it would have a weight of 4.71kg, if going at Mach 4.48 speeds, then KE results: 4.71×1536.64^2×0.5 = 5.56 Megajoules (or 1.32 Kilograms of TNT, Wall Level)

If it were the case that the spear was the weight of the whole building it was made from, it clearly would have a weight well above 100 tons, giving KE results over 10000x times higher to at least city block/Multi city block KE

Feat: https://vsbattles.fandom.com/wiki/User_blog:ElJoaki5/Chainsaw_Man:_Yoru_spins_the_aquarium_spear

 

[LaserPrecision]

Well first of all, you'd want to use rotational kinetic energy for this feat, not ordinary KE. Second, you'd just calculate the acceleration. Then you calculate force with mass x acceleration.

 

[Breadbear83]

You

Well first of all, you'd want to use rotational kinetic energy for this feat, not ordinary KE. Second, you'd just calculate the acceleration. Then you calculate force with mass x acceleration.

Know how to do rotational KE in this feat? I don't get how rotational KE is done

If it matters, Yoru Is grabbing the spear by the middle, does her hand size matters?

 

[Lilybitdun]

To do Rotational KE you have find the mass moment of inertia of the spear

Mass Moment of Inertia Calculator

If you want to find out what is the moment of inertia of an object, our mass moment of inertia calculator is here to help you.

www.omnicalculator.com

You would use the Rod shape and then use Moment of inertia (center) for your rotational KE

You'll need angular velocity as well

Angular Velocity Calculator

This angular velocity calculator finds angular velocity in two ways. You can either use the angle change in the period of time or apply the linear velocity and a given radius.

www.omnicalculator.com

Since you already calculated the speed you can use Method 2 to find the rad/s

And then you're able to use those to find the rotational KE

Rotational Kinetic Energy Calculator

The rotational kinetic energy calculator finds the energy of an object in rotational motion.

www.omnicalculator.com

 

[Breadbear83]

To do Rotational KE you have find the mass moment of inertia of the spear

Mass Moment of Inertia Calculator

If you want to find out what is the moment of inertia of an object, our mass moment of inertia calculator is here to help you.

www.omnicalculator.com

You would use the Rod shape and then use Moment of inertia (center) for your rotational KE

You'll need angular velocity as well

Angular Velocity Calculator

This angular velocity calculator finds angular velocity in two ways. You can either use the angle change in the period of time or apply the linear velocity and a given radius.

www.omnicalculator.com

Since you already calculated the speed you can use Method 2 to find the rad/s

And then you're able to use those to find the rotational KE

Rotational Kinetic Energy Calculator

The rotational kinetic energy calculator finds the energy of an object in rotational motion.

www.omnicalculator.com

in ´´mass moment of inertia´´ part, for the ´´length´´ i use the Spear having a Length of 1.67m like Eljoaki calc says, or something else like the spear having a circumference of 5.26m?

 

[Lilybitdun]

in ´´mass moment of inertia´´ part, for the ´´length´´ i use the Spear having a Length of 1.67m like Eljoaki calc says, or something else like the spear having a circumference of 5.26m?

You would use the 1.67m

 

[Breadbear83]

You would use the 1.67m

last thing, prob a dumb question but for the radius in the method 2 of the angular velocity, do i use half the Spear of 1.67m?

 

[Lilybitdun]

last thing, prob a dumb question but for the radius in the method 2 of the angular velocity, do i use half the Spear of 1.67m?

Yes

 

[Breadbear83]

Well first of all, you'd want to use rotational kinetic energy for this feat, not ordinary KE. Second, you'd just calculate the acceleration. Then you calculate force with mass x acceleration.

do i need certain new values to get acceleration? This Website tells me i need the initial speed and the time to get to final speed (the feat is vague about it, possibly 1 second for the spear to start spinning at those 1536 m/s speeds as before it started spinning the Eternity devil was already close to hit Yoru), or if using ´´mass and force´´ do i put the Spear weight of 4.71kg, and for newtons i use the raw 1.86 Megajoules as 1860000 Newtons or what?

if you or lily are busy, i could ask in CSM thread or calc requests for help for the rest of the calc, i already have the rotational KE done at 1.856 Megajoules

 

[LaserPrecision]

do i need certain new values to get acceleration? This Website tells me i need the initial speed and the time to get to final speed (the feat is vague about it, possibly 1 second for the spear to start spinning at those 1536 m/s speeds as before it started spinning the Eternity devil was already close to hit Yoru), or if using ´´mass and force´´ do i put the Spear weight of 4.71kg, and for newtons i use the raw 1.86 Megajoules as 1860000 Newtons or what?

Since it's a manga, you'll have to use context clues. If she got it to top speed instantly then assume it went from 0 to 1536.52043734 m/s in 0.00171334473 seconds.

(1536.52043734 - 0)/0.00171334473 = 896795.846414 m/s^2

4.71 * 896795.846414 = 4223908.43661 Newtons (430.718 Tons)

 

[Breadbear83]

those 0.0017133 seconds are the time it takes the 1536.52 m/s spear to make half spin, do i use that timeframe or double it for full spin every 0.0034266 seconds?

i may use one of those ends but by doing angsizing i may get how long it may take the devil to hit Yoru, being the timeframe of how long it could had taken Yoru to reach those Speeds of 1536.52 m/s where no parts of the devil gets past to

 

[Lilybitdun]

You should use this to find angular force

Centrifugal Force Calculator

Use our centrifugal force calculator to determine the force acting on a rotating object.

www.omnicalculator.com

 

[Breadbear83]

ok calc ended up like this, im gonna be looking for feedback in CSM discussion thread

 

[LaserPrecision]

those 0.0017133 seconds are the time it takes the 1536.52 m/s spear to make half spin, do i use that timeframe or double it for full spin every 0.0034266 seconds?

Just use the 0.0017133 second timeframe for a half spin. It doesn't matter what you use since either way the angular velocity is the same