Increasing the rate of acceleration using induced gravitational fields

[Jairo Nelson]

Hello, I'm an undergraduate in biomedical engineering, physics, chemistry, and pure mathematics. As you all know, a human can travel at any velocity he/she chooses. The problem arises when the human accelerates to a high velocity in a short period of time (or in other words, accelerates too fast). I was pondering a question about how to decrease the force felt by the human body in motion and therefore increasing the rate at which that person can accelerate. Obviously, the technology is beyond our grasp, but let's say we could induce a gravitational field in any direction we pleased on an aircraft. If we induced a field in the opposite direction of force we felt when we accelerated, could we decrease the amount of force felt..or is that just a hopeful wish? At first I said it was impossible and I still stand by that. But I thought of a classical problem that I need an opinion on. In classical physics, if you take a car (a corolla) and you run it into a wall at 50 mph...it will be damaged in such a way that 25% of the car will be compressed. If that same car is traveling at 100 mph 50% of the car will be compressed in the form of damage. Now, if you run TWO corolla's into each other, both at 50 miles per hour...what is the damage of each car. It has been tested and found that each car experienced only 25% damage compression. This makes sense because the velocity of each car, respectively, does not imply a force. It's the negative acceleration of the car at an instantanious juncture of collision that determines the force. For example: the 50 mph car had an acceleration of -50 as it went from 50mph to 0mph...that multiplied by its mass provided enough force to compress the car to compress it 25% of its length. The 100mph car had an acceleration of -100 since it went from 100mph to 0 mph, and that times its mass provided enough energy to compress the car by 50% of it's original length. Now, when 2 cars of equal mass collide at 50 mph, both denote 25% damage EACH. It's because each car acts as a solid non-moving object with reference to the one colliding into it. Better put, both cars, even though their net velocity was 100mph (both going 50 mph) they only accelerated negatively from 50mph to 0 mph upon collision. But what If you only had one mass? You stand on the earth and even though you feel the constant acceleration of gravity, you are held up by the natural force (in a vague sense of that definition). Would it be possible to match the acceleration of a plane from 0 mph to 2000mph in 30 seconds (which would kill you) by inducing some kind of force in the same direction of your acceleration (or the opposite direction of the force acting upon you as you move through the atmosphere)...and thereby decrease the amount of force felt on the mass...allowing it to accelerate faster than it normally would be able to without inducing death?

[imatfaal]

Hello, I'm an undergraduate in biomedical engineering, physics, chemistry, and pure mathematics. As you all know, a human can travel at any velocity he/she chooses. The problem arises when the human accelerates to a high velocity in a short period of time (or in other words, accelerates too fast). I was pondering a question about how to decrease the force felt by the human body in motion and therefore increasing the rate at which that person can accelerate. Obviously, the technology is beyond our grasp, but let's say we could induce a gravitational field in any direction we pleased on an aircraft. If we induced a field in the opposite direction of force we felt when we accelerated, could we decrease the amount of force felt..or is that just a hopeful wish? At first I said it was impossible and I still stand by that. But I thought of a classical problem that I need an opinion on. In classical physics, if you take a car (a corolla) and you run it into a wall at 50 mph...it will be damaged in such a way that 25% of the car will be compressed. If that same car is traveling at 100 mph 50% of the car will be compressed in the form of damage. Now, if you run TWO corolla's into each other, both at 50 miles per hour...what is the damage of each car. It has been tested and found that each car experienced only 25% damage compression. This makes sense because the velocity of each car, respectively, does not imply a force. It's the negative acceleration of the car at an instantanious juncture of collision that determines the force. For example: the 50 mph car had an acceleration of -50 as it went from 50mph to 0mph...that multiplied by its mass provided enough force to compress the car to compress it 25% of its length. The 100mph car had an acceleration of -100 since it went from 100mph to 0 mph, and that times its mass provided enough energy to compress the car by 50% of it's original length. Now, when 2 cars of equal mass collide at 50 mph, both denote 25% damage EACH. It's because each car acts as a solid non-moving object with reference to the one colliding into it. Better put, both cars, even though their net velocity was 100mph (both going 50 mph) they only accelerated negatively from 50mph to 0 mph upon collision. But what If you only had one mass? You stand on the earth and even though you feel the constant acceleration of gravity, you are held up by the natural force (in a vague sense of that definition). Would it be possible to match the acceleration of a plane from 0 mph to 2000mph in 30 seconds (which would kill you) by inducing some kind of force in the same direction of your acceleration (or the opposite direction of the force acting upon you as you move through the atmosphere)...and thereby decrease the amount of force felt on the mass...allowing it to accelerate faster than it normally would be able to without inducing death?

 

 

A force in the direction opposing your acceleration would just make you accelerate less quickly. You accelerate in the direction of the net force. We feel a force from gravity - that is counteracted by the normal force from the ground in the opposite direction, the net force is zero and whilst we are in contact with the ground we don't accelerate. F=ma is a hard task-master and there is not a simple way to get around it.

[Schrödinger's hat]

The problem is not that you are undergoing an acceleration, it's that the acceleration is caused by forces on one part of your body (ie. your feet or your back).

The way to overcome this would be to exert a homogeneous force on the body of the person being accelerated.

Unfortunately the only such force we know of is gravitational, and there is no known way to manipulate gravitational fields without (large amounts of) mass.

There is research into extremely strong magnetic fields (example) which could be relevant, although I doubt anything over a few g's (maybe 10s of gs?) of acceleration could be managed without ill effects (the human body is not homogeneous and the field will effect different parts of you by different amounts, if the field is too strong it could, for example, rupture all of your arteries by pulling too hard on the blood).

Other staples of science fiction are acceleration beds or chairs where the person is surrounded in a big squishy cushion or a fluid. This acts to distribute the pressure evenly over the entire body (and in the case of the fluid will act as an extra-effective pressure suit, keeping your insides and blood from exploding out your anus).

 

At any rate, our travels for any significant distance (intercontinental, interplanetary or further) will be limited by energy rather than acceleration for what looks to be a very long time -- the main reason rockets accelerate so quickly is to get out of the atmosphere where they waste a lot of energy to drag and to thrusting straight up (there's also a lot to do with energy efficiency deep in a gravitational well, but I digress) -- so a good old one or two gees should do us for most purposes, unless you really want your transatlantic train trip to take less than half an hour.

[michel123456]

(...) Better put, both cars, even though their net velocity was 100mph (both going 50 mph) they only accelerated negatively from 50mph to 0 mph upon collision. (...)

 

Are you sure? What if one car was made of concrete? Wouldn't the 2nd one gets destructed 50%?

[losfomot]

Wouldn't slingshoting your spaceship around a planet allow you a high rate of acceleration without the 'g-force' beating up your body?

[imatfaal]

Wouldn't slingshoting your spaceship around a planet allow you a high rate of acceleration without the 'g-force' beating up your body?

 

Nope fraid not. The 'g's that you feel ARE the acceleration. If anything lessens that force (rather than using techniques to help the body cope with it) then you will simply accelerate less.

 

Just guessing, but in a slingshot manoeuvre surely you would have lateral g to contend with as well

[losfomot]

Nope fraid not. The 'g's that you feel ARE the acceleration. If anything lessens that force (rather than using techniques to help the body cope with it) then you will simply accelerate less.

 

Just guessing, but in a slingshot manoeuvre surely you would have lateral g to contend with as well

 

But in a regular slingshot maneuver (not a 'powered slingshot' maneuver), all the acceleration is due to gravity... so why would you feel a 'g-force'? As long as your rockets aren't firing, you should be weightless the whole time... shouldn't you?

[imatfaal]

If you are accelerating you will feel the force. On human scales it is indistinguishable from gravity; so if your rocket accelerates at 50 ms-2 you will feel 5 'g'. there is no way round it, you can lower the damage/danger caused to the human body, but to get faster you need to accelerate and you cannot shield the passengers from that acceleration

[SMF]

I think that during a gravity assist (planetary slingshot) maneuver a spacecraft is in free fall and would therefore not be subjected to stress from the acceleration, but I am willing to learn different. SM

Edited April 7, 2011 by SMF

[losfomot]

If you are accelerating you will feel the force.

 

Unless that force is due to gravity... as it is in a slingshot maneuver. Jump out of a plane while enclosed within a box... you are accelerating, yet you feel no force (not until you hit the ground).

[imatfaal]

Yep - not sure what I was thinking.