GM
Why woman live longer than men #267
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holy shit that is an epic design for how to safely jump out of a moving vehicle. i wonder what the limit is. let's say the vehicle is an 8 cylinder turbo, cranking 300km/h. how long does the rail have to be to not require more force than a human body can withstand without causing blackout?
The variables
- Velocity change: 80 km/h = 22.2 m/s
- G-force limit for "definitely no blackout": depends on direction and duration
G-force tolerance
Blackout occurs when blood pools away from the brain. Tolerance varies by acceleration
direction:
┌────────────────────┬────────────────────────────────────┬──────────────────────────────┐
│ Direction │ Description │ Untrained tolerance │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ +Gx │ Lying on your back, pushed from │ ~15g short duration │
│ (chest-to-back) │ behind │ │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ -Gx │ Pushed from front │ ~10g short duration │
│ (back-to-chest) │ │ │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ +Gz (head-to-foot) │ Blood pools to feet - worst case │ ~4-6g sustained, higher │
│ │ │ briefly │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ -Gz (foot-to-head) │ Blood pools to head │ ~2-3g │
└────────────────────┴────────────────────────────────────┴──────────────────────────────┘
For sub-second durations (which this will be), tolerance is significantly higher than
sustained values. Roller coasters routinely hit 4-6g briefly with no issues.
The calculation
Using v² = 2as, solving for distance: s = v² / (2 × n × 9.81)
G-force: 2g
Distance: 12.6 m
Duration: 1.13 s
Safety margin: Comfortable for anyone
────────────────────────────────────────
G-force: 3g
Distance: 8.4 m
Duration: 0.75 s
Safety margin: "Definitely safe" for any untrained person in any orientation
────────────────────────────────────────
G-force: 4g
Distance: 6.3 m
Duration: 0.57 s
Safety margin: Safe, brief mild discomfort
────────────────────────────────────────
G-force: 5g
Distance: 5.0 m
Duration: 0.45 s
Safety margin: Safe for sub-second, need correct positioning
The answer
~8.4 metres at 3g is the conservative "definitely no blackout" distance. At 0.75 seconds
duration and 3g, even in the worst orientation (+Gz), an untrained person won't black out.
Most people wouldn't even feel particularly uncomfortable.
A standard flatbed truck tray is 6-8 metres, so this is physically achievable on a large
flatbed. If you orient the person chest-to-back (lying in a reclined seat facing rearward,
acceleration pushes them into the seat), you could safely shorten it to ~5 metres at 5g
with plenty of margin.
The video you saw likely used a rail/sled system running the length of the truck bed with
a controlled acceleration profile - probably something close to these numbers.
The variables
- Velocity change: 80 km/h = 22.2 m/s
- G-force limit for "definitely no blackout": depends on direction and duration
G-force tolerance
Blackout occurs when blood pools away from the brain. Tolerance varies by acceleration
direction:
┌────────────────────┬────────────────────────────────────┬──────────────────────────────┐
│ Direction │ Description │ Untrained tolerance │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ +Gx │ Lying on your back, pushed from │ ~15g short duration │
│ (chest-to-back) │ behind │ │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ -Gx │ Pushed from front │ ~10g short duration │
│ (back-to-chest) │ │ │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ +Gz (head-to-foot) │ Blood pools to feet - worst case │ ~4-6g sustained, higher │
│ │ │ briefly │
├────────────────────┼────────────────────────────────────┼──────────────────────────────┤
│ -Gz (foot-to-head) │ Blood pools to head │ ~2-3g │
└────────────────────┴────────────────────────────────────┴──────────────────────────────┘
For sub-second durations (which this will be), tolerance is significantly higher than
sustained values. Roller coasters routinely hit 4-6g briefly with no issues.
The calculation
Using v² = 2as, solving for distance: s = v² / (2 × n × 9.81)
G-force: 2g
Distance: 12.6 m
Duration: 1.13 s
Safety margin: Comfortable for anyone
────────────────────────────────────────
G-force: 3g
Distance: 8.4 m
Duration: 0.75 s
Safety margin: "Definitely safe" for any untrained person in any orientation
────────────────────────────────────────
G-force: 4g
Distance: 6.3 m
Duration: 0.57 s
Safety margin: Safe, brief mild discomfort
────────────────────────────────────────
G-force: 5g
Distance: 5.0 m
Duration: 0.45 s
Safety margin: Safe for sub-second, need correct positioning
The answer
~8.4 metres at 3g is the conservative "definitely no blackout" distance. At 0.75 seconds
duration and 3g, even in the worst orientation (+Gz), an untrained person won't black out.
Most people wouldn't even feel particularly uncomfortable.
A standard flatbed truck tray is 6-8 metres, so this is physically achievable on a large
flatbed. If you orient the person chest-to-back (lying in a reclined seat facing rearward,
acceleration pushes them into the seat), you could safely shorten it to ~5 metres at 5g
with plenty of margin.
The video you saw likely used a rail/sled system running the length of the truck bed with
a controlled acceleration profile - probably something close to these numbers.
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