4 ms·

I don't understand how anyone can believe it's safer to be unrestrained and free to bounce around the cabin in a crash. It's definitely cheaper, though. And, m

by brian6 16y ago

I don't understand how anyone can believe it's safer to be unrestrained and free to bounce around the cabin in a crash. It's definitely cheaper, though. And, maybe more importantly, banning kids who won't stay buckled up would be very unpopular.

kbatten 16y ago
People's beliefs generally have very little to do with actually keeping people safe.
nck4222 16y ago
"And, maybe more importantly, banning kids who won't stay buckled up would be very unpopular." More importantly, that would likely result in more kids being killed by taking less safe modes of transportation to school (EDIT: if the article is true anyway).
blhack 16y ago
>I don't understand how anyone can believe it's safer to be unrestrained and free to bounce around the cabin in a crash. Did you read the article? That is the point; most people share your view. Buses are safer because the tightly packet seats act like little pods of foam, like little safety bubbles. If the bus hits something, it's 4 inches of foam that the kid is going to hit...basic physics, f=ma, a=v/t...the foam increases the time it takes the moving body to slow to a stop, and spreads the force over a longer period of time. Since it would be instantaneous, not aggregate (I'm making both of those terms up, no idea what you would actually call this) force that you care about, a longer time at a lower force == a safer collision. Think about it like this: you have two buckets, one of them is called "child" and the other called "seat". These two buckets contain a liquid called "momentum". If the bus hits a brick wall, all of the momentum from the child is going to get transferred into the "seat" bucket. The interstitial bucket you use to transfer this liquid is called "force". The foam seat means that you're using a little tiny thimble to transfer the momentum from the child to the seat...it takes a long time, and it isn't very big...it's "gradual". It's counter-intuitive, but that is one of the reasons that buses are safe.
- wuputah 16y ago
  While we're here talking about physics: another big reason why buses are safe are because of their high mass. I was in one accident while on a school bus - another car hit the bus head-on while the bus was stopped. The kinetic energy of the 1 ton car travelling at say 30 mph - 1/2 * m * v^2 - was absorbed by the bus. I won't step through the math, but because of the high mass of the bus, the resulting velocity of the bus+car was quite low (it also helped that the change in velocity was mitigated by brakes/tires/friction, as the driver was ready for the impact). In any case, as a passenger on the bus, the result of the impact was quite minimal - there were no injuries on the bus, and the bus actually drove off afterwards (with no passengers and a bit of sheet metal scraping the pavement). Granted, it's a different story if the bus hits a tree or is hit by a tractor trailer doing 70 mph. Another reason why buses are safe? The bus is operated by a trained professional, most of which have years of experience driving the bus for hours every day.
  - klbarry 16y ago
    My own experienceL My school bus when I was young hit into the side of a van and sent it physically flying and rolling. We barely felt it in the back.
  - jpr 16y ago
    I have often wondered about the difference in accident rates between professional and other drivers, anyone know if there are any studies done on this?
- Jach 16y ago
  To compliment your explanation, here's some math. Newton's law: F = m* a = m* dv/dt. If we assume the child and bus seat's masses are constant (no exploding kids, please!), this leads to F = d(m* v)/dt = dp/dt where p is momentum. When the child hits the foam seat, the force will not remain constant, that is it varies with time, leading from the above to dp = F* dt. We can find the change in momentum by integrating Force with respect to Time, leading to (in LaTeX notation) p_f - p_i = \int_{t_i}^{t_f}(F* dt) = I where I stands for Impulse. The time-averaged force F' = 1/delta(t) * I = 1/delta(t) * delta(p), and this is where I think it becomes very clear that we like to have longer collision times for less damage. If we're interested in having a smaller average force for when the child hits the seat, then either delta(t) needs to be longer (the collision takes a longer time, due to e.g. the foam seat, the bumpers on cars, collapsible sections of the vehicle, etc.), or the change in momentum of the child needs to be smaller (e.g. if the collision is inelastic and the seat brings the child's velocity to 0, that is better than the seat bouncing the child back). It's easy to add another layer of foam. Possibly the funnest lab in my high school physics class: shooting an egg at a brick wall and having it survive unharmed by encasing it in some design. (Mine was the Hindenburg of Bubblewrap.)
Travis 16y ago
It's not a matter of absolute level of safety (is it more or less sage), it's a matter of cost/benefit. And a matter of diminishing returns. Yes, it sucks that 6 kids per year still die in a tragic manner. Horrific for the family. But the article is pointing out that busses are already much safer than more common forms of transporting. So the issue isn't one of more safety, less safety. If we could afford every convenience, then more safety would be better. But you cannot take safety in isolation without consider other factors, such as cost, rate of accidents, etc.
bryanlarsen 16y ago
It's safer because kids will misuse seat belts and strangle themselves in a crash rather than be safely absorbed by the seat in front of them.

by brian6 16y ago

kbatten 16y ago

People's beliefs generally have very little to do with actually keeping people safe.

nck4222 16y ago

"And, maybe more importantly, banning kids who won't stay buckled up would be very unpopular." More importantly, that would likely result in more kids being killed by taking less safe modes of transportation to school (EDIT: if the article is true anyway).

blhack 16y ago

>I don't understand how anyone can believe it's safer to be unrestrained and free to bounce around the cabin in a crash. Did you read the article? That is the point; most people share your view. Buses are safer because the tightly packet seats act like little pods of foam, like little safety bubbles. If the bus hits something, it's 4 inches of foam that the kid is going to hit...basic physics, f=ma, a=v/t...the foam increases the time it takes the moving body to slow to a stop, and spreads the force over a longer period of time. Since it would be instantaneous, not aggregate (I'm making both of those terms up, no idea what you would actually call this) force that you care about, a longer time at a lower force == a safer collision. Think about it like this: you have two buckets, one of them is called "child" and the other called "seat". These two buckets contain a liquid called "momentum". If the bus hits a brick wall, all of the momentum from the child is going to get transferred into the "seat" bucket. The interstitial bucket you use to transfer this liquid is called "force". The foam seat means that you're using a little tiny thimble to transfer the momentum from the child to the seat...it takes a long time, and it isn't very big...it's "gradual". It's counter-intuitive, but that is one of the reasons that buses are safe.

wuputah 16y ago
While we're here talking about physics: another big reason why buses are safe are because of their high mass. I was in one accident while on a school bus - another car hit the bus head-on while the bus was stopped. The kinetic energy of the 1 ton car travelling at say 30 mph - 1/2 * m * v^2 - was absorbed by the bus. I won't step through the math, but because of the high mass of the bus, the resulting velocity of the bus+car was quite low (it also helped that the change in velocity was mitigated by brakes/tires/friction, as the driver was ready for the impact). In any case, as a passenger on the bus, the result of the impact was quite minimal - there were no injuries on the bus, and the bus actually drove off afterwards (with no passengers and a bit of sheet metal scraping the pavement). Granted, it's a different story if the bus hits a tree or is hit by a tractor trailer doing 70 mph. Another reason why buses are safe? The bus is operated by a trained professional, most of which have years of experience driving the bus for hours every day.
- klbarry 16y ago
  My own experienceL My school bus when I was young hit into the side of a van and sent it physically flying and rolling. We barely felt it in the back.
- jpr 16y ago
  I have often wondered about the difference in accident rates between professional and other drivers, anyone know if there are any studies done on this?
Jach 16y ago
To compliment your explanation, here's some math. Newton's law: F = m* a = m* dv/dt. If we assume the child and bus seat's masses are constant (no exploding kids, please!), this leads to F = d(m* v)/dt = dp/dt where p is momentum. When the child hits the foam seat, the force will not remain constant, that is it varies with time, leading from the above to dp = F* dt. We can find the change in momentum by integrating Force with respect to Time, leading to (in LaTeX notation) p_f - p_i = \int_{t_i}^{t_f}(F* dt) = I where I stands for Impulse. The time-averaged force F' = 1/delta(t) * I = 1/delta(t) * delta(p), and this is where I think it becomes very clear that we like to have longer collision times for less damage. If we're interested in having a smaller average force for when the child hits the seat, then either delta(t) needs to be longer (the collision takes a longer time, due to e.g. the foam seat, the bumpers on cars, collapsible sections of the vehicle, etc.), or the change in momentum of the child needs to be smaller (e.g. if the collision is inelastic and the seat brings the child's velocity to 0, that is better than the seat bouncing the child back). It's easy to add another layer of foam. Possibly the funnest lab in my high school physics class: shooting an egg at a brick wall and having it survive unharmed by encasing it in some design. (Mine was the Hindenburg of Bubblewrap.)

Travis 16y ago

It's not a matter of absolute level of safety (is it more or less sage), it's a matter of cost/benefit. And a matter of diminishing returns. Yes, it sucks that 6 kids per year still die in a tragic manner. Horrific for the family. But the article is pointing out that busses are already much safer than more common forms of transporting. So the issue isn't one of more safety, less safety. If we could afford every convenience, then more safety would be better. But you cannot take safety in isolation without consider other factors, such as cost, rate of accidents, etc.

bryanlarsen 16y ago

It's safer because kids will misuse seat belts and strangle themselves in a crash rather than be safely absorbed by the seat in front of them.