Very odd question but, how much does a speed bump weigh?

[Traab]

Im trying to find that out so I have the basis for some math to work with. Im reading a webcomic where there is a super battle going on. One of the bad guys has picked up one of those parking lot speed bumps and hurled it at a hero, only for it to be deflected. I wanted to do some math and find out roughly how much force was involved in that. Just as a point of reference, im going to assume it was thrown like a javelin which professionals can hurl upwards of 70 mph. So maybe that can get added to the question, how much does a speed bump weigh, and how much force would it hit a target with if thrown at 70 mph?

[Grinner]

Any idea what material they're made of?

[Rakaydos]

Speed bump, or parking bumper?

[Traab]

Speed bump, or parking bumper?

Damn, im not sure, actually, looking at it here (http://grrlpowercomic.com/archives/1393) it may be a parking bumper. I didnt even consider that, I thought speed bump but its a bit too square and tall for that.

*EDIT* As for material im assuming concrete?

[noparlpf]

Speed bumps are usually made of asphalt and built into the road. Those things ("Parking bumper" works I guess? Never thought to call them something.) are concrete, sometimes with an iron bar or two inside for stability. You can work from there with the average density of concrete. Google gives me about 2.4 g/cc, courtesy of Wikipedia. Say those things are maybe five feet long, six inches wide, six inches high. Rounding off and pretending they're just rectangular prisms, that's around 34,000 ccs. Call it roughly 82,000 g or 82 kilos. About as much as a largeish adult man.

Edit: This site (http://www.modernprecast.com/parking_bumpers.html) sells them. Theirs are six feet by nine inches by five inches. If you want to factor in the shape, that's around 47,000 ccs. So call it about 113 kilos. Two smallish adult men.

[Traab]

Hmm, ok, so if you were to hurl one like a spear at 70 mph, how much force would it deliver on impact? I admit im really crappy with the math, I think it force equals mass times acceleration, so would that mean 82 kilos x 70mph = 5740 kilos or 12600+ pounds of force?

*EDIT* Blarg, ok, so 113 x 70 = 7910 kilos of force or 17438 pounds of force?

[noparlpf]

Miles per hour is velocity, not acceleration. Let's see...the momentum would be (110kg*32m/s)=3520(m*kg/s) (back in Physics 100, I got fed up with that and invented a unit based on my initials; the professor was amused and let it pass). Uhh. I don't remember how to get force out of these things. I can give you the kinetic energy at that velocity; that's (.5*110kg*(32m/s)²)=56.3 kJ. I think that's roughly equivalent to the kinetic energy of the average adult human falling from around a hundred meters. All I can tell you is that it's bad when a solid object (a concrete bar, the ground) hits a human with that much energy.

[Traab]

Miles per hour is velocity, not acceleration. Let's see...the momentum would be (110kg*32m/s)=3520(m*kg/s) (back in Physics 100, I got fed up with that and invented a unit based on my initials; the professor was amused and let it pass). Uhh. I don't remember how to get force out of these things. I can give you the kinetic energy at that velocity; that's (.5*110kg*(32m/s)²)=56.3 kJ. I think that's roughly equivalent to the kinetic energy of the average adult human falling from around a hundred meters. All I can tell you is that it's bad when a solid object (a concrete bar, the ground) hits a human with that much energy.

Rofl, yeah, I would imagine it might sting a little.... as it passes completely through you..... and the wall behind you. The main reason I was interested was, after the linked comic, the main character uses one of her abilities to deflect a hurled parking bumper and I was curious as to how much force it would take to stop it dead in its tracks like she did. According to the drawing she didnt deflect it, she knocked it perpendicular to its course and it actually bounced backwards after it hit the ground. Earlier on in the comic she mentions the largest thing she had lifted with that tentacle was her car and I was curious to see how these events matched up. Im thinking it required way more power to stop the thrown slab of concrete than to lift a car, but im not sure.

[gomipile]

Speed bumps are usually made of asphalt and built into the road.

Not around here. Here they're made of steel or a dense, very tough reinforced concrete and bolted to anchors embedded in the pavement. The reason is that they have to be removed for the snowy seasons so that snowplows won't hit them.

[BannedInSchool]

The F=ma is an instantaneous number at a moment in time. You can gloss over integrating force over time and just use momentum and energy to figger out velocities before and after the collision. Just for example, two cars that weigh the same will have the same amount of momentum and energy when they crash into a wall, but the one that's built to crumple properly will have lower peak deceleration even though they both end up at zero velocity. The crumpling one will have lower force over longer time to sum up to the same change in momentum. People not being so elastic would mean both the person and the parking bumper would be going ~35-45mph after the collision (saying the person masses one-half to equal to the bumper), with that acceleration happening over a not very great distance and time. Not a joyride. :smallsmile:

But for Sydney's tentacle you could figure out what constant force and acceleration it would take to deflect the bumper. You'd have to pick either a time or a distance that you're using to solve for the other, though. Or you could assume the force it took to lift the car and see how far off from instantly that is for the bumper. I tried to do the math but I'm not so awake right now. And "power" is an entirely different unit of applying force over a distance divided by the time taken. A hand jack still lifts a car; it just doesn't do it with a lot of velocity and power. :smallsmile: Applying that that lifting force at 70mph is a lot more power.

[factotum]

Yeah, time is an important factor here. To (almost) instantly stop a projectile like this dead in its tracks would take considerably more force than, say, moving it aside a couple of feet over the fraction of a second of its flight so it misses the target.

However, the linked strip suggests that the white-haired woman neither stops nor deflects the object--she puts up some sort of thin barrier that causes the thing to snap in half and pass either side of her; the two pieces still seem to be travelling pretty fast as they go past (they're a good distance behind her in the next panel). I suspect the force required to do that would be considerably less than to actually stop the object, for the same reason that it's a lot easier to cut through a block of cheese with the sharp side of the knife than the back side of it.

[noparlpf]

Not around here. Here they're made of steel or a dense, very tough reinforced concrete and bolted to anchors embedded in the pavement. The reason is that they have to be removed for the snowy seasons so that snowplows won't hit them.

Huh. We just have signs saying "raise plow".

[Traab]

Yeah, time is an important factor here. To (almost) instantly stop a projectile like this dead in its tracks would take considerably more force than, say, moving it aside a couple of feet over the fraction of a second of its flight so it misses the target.

However, the linked strip suggests that the white-haired woman neither stops nor deflects the object--she puts up some sort of thin barrier that causes the thing to snap in half and pass either side of her; the two pieces still seem to be travelling pretty fast as they go past (they're a good distance behind her in the next panel). I suspect the force required to do that would be considerably less than to actually stop the object, for the same reason that it's a lot easier to cut through a block of cheese with the sharp side of the knife than the back side of it.

She basically forms a blade of lightning or some similar level of energy like a freaking plasma cutter, but she isnt the one I was talking about. In the next strip the main character sydney uses what amounts to a glowing tentacle of energy to basically pimp slap the thrown object in mid flight. She hits it hard enough to cancel out its forward momentum completely, send it flying sideways a bit, and it actually bounces backward after it hits the ground.

[gomipile]

Huh. We just have signs saying "raise plow".

I could make a joke about our plow drivers not being likely to read such a sign, but I'll post this sentence in lieu of that.

A better reason would be that we sometimes get sticky snow that clings to horizontal surfaces. During a snowstorm, one cannot necessarily depend on being able to read any signs around here.

[BannedInSchool]

Right, so momentum of 3520m*kg/s for the concrete bar, call it a force of around 10000kg*m/s^2 for supporting a small car or an end of a larger car with the tentacle, gives us 0.352s to just stop it. Sanity check: m=110kg, F=10000N, a=F/m=90.91m/s^2, a*t=90.91m/s^2*0.352s=32m/s and our assumed starting velocity. Check. Distance travelled: 0.5at^2+vt = -0.5*90.91*0.352^2(m/s^2*s^2)+32*0.352(m/s*s) = 5.63m, or half the distance it would have traveled in that time at the initial velocity. Not instant in time or distance with that presumed acceleration. As a 10G impact that wouldn't be bad as a 70mph car crash coming to a stop in 18ft. Also knowing that car crashes into solid objects can be around 100G is another check on that. Bump that acceleration (and force from the tentacle) up ten times to 100G and we get distance and time reduced to a tenth, or 0.03s and 0.56m, which is about right, at least order of magnitude, for an into-wall crash too.

But the short of it is that the tentacle would need to apply a force of a lot more than just holding a car to slap aside the concrete bar anything like what's depicted. It should also go spinning off, likely, because it'd be hard to hit it in a way that didn't produce a torque. Go ahead, have someone throw pencils at you and knock them aside with your finger. :smallsmile:

[Traab]

Right, so momentum of 3520m*kg/s for the concrete bar, call it a force of around 10000kg*m/s^2 for supporting a small car or an end of a larger car with the tentacle, gives us 0.352s to just stop it. Sanity check: m=110kg, F=10000N, a=F/m=90.91m/s^2, a*t=90.91m/s^2*0.352s=32m/s and our assumed starting velocity. Check. Distance travelled: 0.5at^2+vt = -0.5*90.91*0.352^2(m/s^2*s^2)+32*0.352(m/s*s) = 5.63m, or half the distance it would have traveled in that time at the initial velocity. Not instant in time or distance with that presumed acceleration. As a 10G impact that wouldn't be bad as a 70mph car crash coming to a stop in 18ft. Also knowing that car crashes into solid objects can be around 100G is another check on that. Bump that acceleration (and force from the tentacle) up ten times to 100G and we get distance and time reduced to a tenth, or 0.03s and 0.56m, which is about right, at least order of magnitude, for an into-wall crash too.

But the short of it is that the tentacle would need to apply a force of a lot more than just holding a car to slap aside the concrete bar anything like what's depicted. It should also go spinning off, likely, because it'd be hard to hit it in a way that didn't produce a torque. Go ahead, have someone throw pencils at you and knock them aside with your finger. :smallsmile:

Whew, thats a lot of numbers, but thanks for the help. So if the author had any idea what he was doing when he drew sydney deflecting that lump of concrete, then he would have to be aware that the pseudopod tentacle thing she used is way stronger than lifting a car. Which would mean that by using that, she is actually well into the superstrong level, even if not remotely close to the top. (Honestly, comic wise, I count easily lifting a car to be the bottom rung of super strength, so if she can do way more than that, she probably ranks lower middle to middle super strong range) Hmm, dang, that will come in seriously handy then. Even though there are a number of far stronger heroes on her side, the adaptability of the tentacle will give her a lot of flexibility when it comes to moving heavy objects without endangering herself in the process. Ehhh, never mind me, im just thinking as I type.

[BannedInSchool]

Whew, thats a lot of numbers, but thanks for the help. So if the author had any idea what he was doing when he drew sydney deflecting that lump of concrete, then he would have to be aware that the pseudopod tentacle thing she used is way stronger than lifting a car.
Eh, depends on how the tentacle works. Collisions require a lot of force because they produce a change in momentum over a very short time, but that doesn't necessarily mean the tentacle can sustain that force. It could act like it has it's own mass and inertia in a collision. That would also mean Sydney could whip it (good) for extra impact. Or maybe it can momentarily produce a much larger force, or only when stationary.

Oh, another comparison, if we keep the 100kg concrete bar moving at 31m/s (70mph), that's the velocity it'd hit the ground if dropped from 50m (160ft) and a 3.2s fall. I think intuitively that shows it's going to be quite an impact to stop it near instantly. More than jacking up a car where it landed. :smallwink:

[SiuiS]

Damn, im not sure, actually, looking at it here (http://grrlpowercomic.com/archives/1393) it may be a parking bumper. I didnt even consider that, I thought speed bump but its a bit too square and tall for that.

*EDIT* As for material im assuming concrete?

That is 100% a cement parking bumper. If you look at the broken thing you can see a single hole on the bottom on either side. This is for the rebar posts which anchor it in place.

From that you could find the average weight of concrete and guess at the size of the bumper based on the person (not all of them are the same size). I have one at work, I'll see if I can measure it enough to give you dimensions. The one I have can be kicked around, not aerially but moved by single foot with little trouble. I would guess it's in the 20-30 pound range.