6 ms·

You mean objects with lower surface area to mass ratio, AKA objects with lower density. If he wants some high-density objects to throw I think there are stores

You mean objects with lower surface area to mass ratio, AKA objects with lower density. If he wants some high-density objects to throw I think there are stores in the US that sell small, dense metal objects he could use.

dragontamer 5y ago
Mass is not a factor in drag equations. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/vel.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a... Velocity-squared is the factor in drag.
- bernulli 5y ago
  But very much in inertia, which is acting against the drag, trying to sustain its initial velocity. https://en.wikipedia.org/wiki/Ballistic_coefficient https://en.wikipedia.org/wiki/Ballistic_coefficient
- jpollock 5y ago
  Density is important when comparing two spheres of the same mass. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/shaped.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a... Where frontal volume is determined by mass and density for a sphere. So, two speheres with the same mass, but different densities will have different drag forces.
  - deleted 5y ago
    [deleted]
  - dragontamer 5y ago
    That's density of air, not of the object. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/atmos.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a...
    - cinquemb 5y ago
      I wonder if you could do something like this[0] on the projectile to reduce drag: "It is reported that femtosecond-duration laser pulse can be deployed to reduce drag for blunt-body vehicle in high-Mach flow field of air by generating laser plasma and shockwave. The interaction of plasma shockwave induced by femtosecond-duration laser pulse and bow shock over the head of the blunt-body vehicle is investigated numerically in the flow field of 30 km apart from the surface of the earth at Mach number of 5 and the mechanism of deploying the femtosecond laser plasma to reduce the drag of the vehicle is analyzed. The Navier-Stokes equations are exploited to compute the drag reduction for different femtosecond laser energies. The present numerical experiment proves that the femtosecond laser pulse has a better drag reduction effect than the nanosecond laser pulse under the same condition. When the femtosecond laser energy is 0.06 mJ, the femtosecond laser plasma can reduce the drag by 98%. And the higher the energy of femtosecond laser pulse, the higher the drag reduction ratio and the longer the time of low drag. Deploying three femtosecond laser energy point to reduce the drag of hypersonic vehicle is much more obviously. This energy-deposition mode can improve the optimum drag reduction ratio and save the laser energy." Probably out of the scope for a $200 build, but maybe in the scope of a $2000, $20000, or $200000 build? I also wonder if iterating on the above, combined with a concentrated solar power plant of arbitrary sized solar field that could provide enough energy for a railgun to launch payload with femtosecond laser plasma capabilities out of earths gravity well? Maybe, we could escape from the Goddard age eventually lol [0] https://www.researchgate.net/publication/282709902_Exploring_Femtosecond_Laser_Plasma_to_Reduce_Drag_of_Hypersonic_Vehicle https://www.researchgate.net/publication/282709902_Exploring...
      - bernulli 5y ago
        The laser in the study is moving with the projectile, so I guess even for $2000 you won’t be able to have a 30 km altitude, Mach 6 flying object with perfectly controlled laser launched from a trebuchet.
        cinquemb 5y ago
        I'm talking about a projectile that has the laser capabilities in itself (i.e the electromagnetic slug is emitting the femtosecond laser pulses after it is launched), not launched via a laser (it could be launched however, but I was assuming later on the comment that both the rail gun and the slug itself will need to be charged up).

dragontamer 5y ago

Mass is not a factor in drag equations. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/vel.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a... Velocity-squared is the factor in drag.

bernulli 5y ago
But very much in inertia, which is acting against the drag, trying to sustain its initial velocity. https://en.wikipedia.org/wiki/Ballistic_coefficient https://en.wikipedia.org/wiki/Ballistic_coefficient
jpollock 5y ago
Density is important when comparing two spheres of the same mass. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/shaped.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a... Where frontal volume is determined by mass and density for a sphere. So, two speheres with the same mass, but different densities will have different drag forces.
- deleted 5y ago
  [deleted]
- dragontamer 5y ago
  That's density of air, not of the object. https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/atmos.html https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/a...
  - cinquemb 5y ago
    I wonder if you could do something like this[0] on the projectile to reduce drag: "It is reported that femtosecond-duration laser pulse can be deployed to reduce drag for blunt-body vehicle in high-Mach flow field of air by generating laser plasma and shockwave. The interaction of plasma shockwave induced by femtosecond-duration laser pulse and bow shock over the head of the blunt-body vehicle is investigated numerically in the flow field of 30 km apart from the surface of the earth at Mach number of 5 and the mechanism of deploying the femtosecond laser plasma to reduce the drag of the vehicle is analyzed. The Navier-Stokes equations are exploited to compute the drag reduction for different femtosecond laser energies. The present numerical experiment proves that the femtosecond laser pulse has a better drag reduction effect than the nanosecond laser pulse under the same condition. When the femtosecond laser energy is 0.06 mJ, the femtosecond laser plasma can reduce the drag by 98%. And the higher the energy of femtosecond laser pulse, the higher the drag reduction ratio and the longer the time of low drag. Deploying three femtosecond laser energy point to reduce the drag of hypersonic vehicle is much more obviously. This energy-deposition mode can improve the optimum drag reduction ratio and save the laser energy." Probably out of the scope for a $200 build, but maybe in the scope of a $2000, $20000, or $200000 build? I also wonder if iterating on the above, combined with a concentrated solar power plant of arbitrary sized solar field that could provide enough energy for a railgun to launch payload with femtosecond laser plasma capabilities out of earths gravity well? Maybe, we could escape from the Goddard age eventually lol [0] https://www.researchgate.net/publication/282709902_Exploring_Femtosecond_Laser_Plasma_to_Reduce_Drag_of_Hypersonic_Vehicle https://www.researchgate.net/publication/282709902_Exploring...
    - bernulli 5y ago
      The laser in the study is moving with the projectile, so I guess even for $2000 you won’t be able to have a 30 km altitude, Mach 6 flying object with perfectly controlled laser launched from a trebuchet.
      - cinquemb 5y ago
        I'm talking about a projectile that has the laser capabilities in itself (i.e the electromagnetic slug is emitting the femtosecond laser pulses after it is launched), not launched via a laser (it could be launched however, but I was assuming later on the comment that both the rail gun and the slug itself will need to be charged up).