Dropping to flat
Comments
-
Vertical depth into the polystyrene should be the same if the initial conditions both started with no vertical motion.0
-
TommyEss wrote:Dropped from one foot up the bullet will have gravitational potential energy equal to it's mass in kg multiplied by the acceleration due to gravity squared.
When fired from a gun I think you'll find it has rather more energy imparted to it from the gunpowder than a one foot drop would give it, so it's not a fair comparison.
But is that not just the same situation? If you hit the drop at 30 mph you have much more energy than if you were simply dropped the same height?0 -
supersonic wrote:Vertical depth into the polystyrene should be the same if the initial conditions both started with no vertical motion.
But, and the key point here, the horizontal depth (length) would not be the same.0 -
GHill wrote:supersonic wrote:Vertical depth into the polystyrene should be the same if the initial conditions both started with no vertical motion.
But, and the key point here, the horizontal depth (length) would not be the same.
I know - we seem to be debating two things here. I alluded to your point in the ground conditions earlier, as did a few others. It is the condition of the ground that is the key on what we feel as 'impact'. You land on the worlds best velcro with velcro tyres and you are going over the bars ;-). The bike hits the ground (downwards) no harder though, no matter what the velocity. If the suspension was purely in the Y direction, they would not compress any further at 1mph or 100mph. The fact the forks are not is yet another factor lol.
Assuming the rider does not budge on impact.0 -
I would say that the bullet from the gun will dig in the same amount, vertically, as the dropped one. But would create a long 'trough' in the polystyrene.
0 -
Assuming firstly your head is smooth and shiny(!), and the ball is smooth and shiny too...
A ball dropped from 10m from directly above you, hits your head.
Bump - what you feel is all the gravitational potential energy converted in kinetic energy so it moves towards your head. Since gravity is constant (-ish for the geeks) the factor that affects how hard it hits your head is solely down to the mass of the ball - or it's weight - which is a function of it's mass and the acceleration due to gravity (a man on the moon weighs a lot less, but his mass is exactly the same)
For the ball to hit your head harder, we need to either increase the force of gravity (tricky), increase the mass of the ball (need a new ball) or lift the ball higher (giving it more potential energy - so it will hit you at a faster speed - and transmit more force to your head)
Now, if we toss the ball at your head from the side, at the same height as your head - so it just glances your bonce - you'll barely feel anything - because the ball is moving only sideways, and there is no downwards movement at all.
But what if we throw it from above AND to the side? Well now it has both a vertical and a horizontal movement - but we've used the same ball and are dropping it from the same height (gravity's the same too, thank God) - so what does it feel like when it hits your head?
The downwards movement comes from the height and the mass - which we've already said is the same - so it feels the same when it hits you!Cannondale Synapse 105, Giant Defy 3, Giant Omnium, Giant Trance X2, EMC R1.0, Ridgeback Platinum, On One Il Pompino...0 -
GHill wrote:TommyEss wrote:Dropped from one foot up the bullet will have gravitational potential energy equal to it's mass in kg multiplied by the acceleration due to gravity squared.
When fired from a gun I think you'll find it has rather more energy imparted to it from the gunpowder than a one foot drop would give it, so it's not a fair comparison.
But is that not just the same situation? If you hit the drop at 30 mph you have much more energy than if you were simply dropped the same height?
Yes - but how far forwards you travel has nothing to do with how high up you are (not entirely true, as you will probably fall to the next level before you've run out of forward movement - since you can't properl yourself through the air and give yourself extra kinetic energy in the air)
Look at ski jumpers though - they're falling and moving forwards - but they're flying over a slope - so they don't land until they've completly run out of forwards movement...Cannondale Synapse 105, Giant Defy 3, Giant Omnium, Giant Trance X2, EMC R1.0, Ridgeback Platinum, On One Il Pompino...0 -
Ahhh I see what you are getting at I think:
At a higher speed you will decelerate more, yes that is true, I have been blind to that.
Was that an initial question?
If you are moving faster the friction will be higher... So therefore with more horizontal speed off a drop, the moment you hit the ground, you will lose more speed than if you were going slower... If you get me
Sorry GHill, I see now what you mean :oops:
But still, it won't affect your impact you feel0 -
albo wrote:But still, it won't affect your impact you feel
It won't affect how hard your nads hit the top tube - but it might make them slide on and into the headset...Cannondale Synapse 105, Giant Defy 3, Giant Omnium, Giant Trance X2, EMC R1.0, Ridgeback Platinum, On One Il Pompino...0 -
fitch28 wrote:
Elementary, My Dear Watson... 8)0 -
The effect will be the same, it's a small curb. given the same sized drop, speed (in the horizontal x direction) does NOT make a difference.GHill wrote:If you want to convince yourself that the horizontal motion makes a difference think of a car dropping off a small curb. At 5 mph the effect will be a bump but nothing to worry about. At 150 mph it will be a big deal (serious or possibly terminal damage).
Don't try this at home.
edited for clarity.0 -
Right, regarding the original question, how about this explanation to clarify why rear wheel first landings are better.
if you stand on a 4 foot high wall and simply step off, landing vertically with your legs straight you'll feel a hell of an impact on your legs and feet because you just fell 4 feet.
Now (if you can still walk) try the same, but this time, sit on your bum, with your legs dangling over the edge before sliding off. This time your feet have dropped far less, since they were lower to the ground to start with. The impact is far less, and you should feel little or no discomfort on landing.
The rear-wheel landing on a bike is similar to the second drop, since you're extending your legs to meet the ground, and therefore reducing the height dropped. Your rear wheel will meet the ground much sooner, meaning you gain less acceleration from falling.
How does that strike people? make sense?
Right then, let's get back into the business of educating people about simple physics. 0 -
This thread is growing as fast as the "What lights" one You don't need eyes to see, you need vision0
-
What flights?!0
-
yeehaamcgee wrote:The rear-wheel landing on a bike is similar to the second drop, since you're extending your legs to meet the ground, and therefore reducing the height dropped. Your rear wheel will meet the ground much sooner, meaning you gain less acceleration from falling.
I'm going to regret this...
I don't buy the above. In the sitting jump, every bit of your body starts closer to the ground than a standing jump, so has less time to accelerate. No matter how you land on a bike, the bike and you start at the same hight. So downwards acceleration is the same. In fact, if you drive down the rear end, its acceleration will be higher and so will the vertical speed when it hits the ground.
But in answer to the OP, I'd just huck a few and see what goes best!0 -
less fights about lights than flights
You don't need eyes to see, you need vision0 -
lochussie wrote:yeehaamcgee wrote:The rear-wheel landing on a bike is similar to the second drop, since you're extending your legs to meet the ground, and therefore reducing the height dropped. Your rear wheel will meet the ground much sooner, meaning you gain less acceleration from falling.
I'm going to regret this...
I don't buy the above. In the sitting jump, every bit of your body starts closer to the ground than a standing jump, so has less time to accelerate. No matter how you land on a bike, the bike and you start at the same hight. So downwards acceleration is the same. In fact, if you drive down the rear end, its acceleration will be higher and so will the vertical speed when it hits the ground.
But in answer to the OP, I'd just huck a few and see what goes best!
No, I agree with yehaa here. Maybe his example of a person jumping off a wall wasn't too accurate - here you start nearer the ground. But if you start in a crouching position with your legs bent, then extend them as you fall and bend them again as you land, then the impact will be less than if you had just stepped off the wall standing up."Melancholy is incompatible with bicycling." ~James E. Starrs0 -
Ah, but your center of mass doesn't "fall" any quicker, you're simply extending your limbs, well, legs, to use as shock absorbers.lochussie wrote:yeehaamcgee wrote:The rear-wheel landing on a bike is similar to the second drop, since you're extending your legs to meet the ground, and therefore reducing the height dropped. Your rear wheel will meet the ground much sooner, meaning you gain less acceleration from falling.
I'm going to regret this...
I don't buy the above. In the sitting jump, every bit of your body starts closer to the ground than a standing jump, so has less time to accelerate. No matter how you land on a bike, the bike and you start at the same hight. So downwards acceleration is the same. In fact, if you drive down the rear end, its acceleration will be higher and so will the vertical speed when it hits the ground.
But in answer to the OP, I'd just huck a few and see what goes best!
The great thing about this one? it's really really easy to prove. Just go do it.
If you REALLY really don't believe me, just do it. Then you will.0 -
Yeah, I agree that the overall deceleration and so force will prob be less if you land trials like and bend legs a lot than if you land flat and bend legs and arms a bit.0
-
so.... that concludes the main point of this thread right?
anyway, back to the sciency bit.
Who wants to see a quick sketch of the principle behind the transition that matches your trajectory at the point of contact?
(although I suspect there are now a few more people in this thread who understand, so this may no longer be neccesary)0 -
all the transition does is provide a slower (less severe) vertical decelaration than landing to flat and therefore the forces on the bike and your body are less.
same principle as crumple zones on cars0 -
I know. The reason for that is because you don't come to a stop vertically, you simply lose speed in the y axis.yoohoo999 wrote:all the transition does is provide a slower (less severe) vertical decelaration than landing to flat and therefore the forces on the bike and your body are less.
same principle as crumple zones on cars
It is entirely possible to not lose any vertical speed though, by having a slope that just impedes your downwards acceleration.0 -
Akin to terminal velocity?0
-
Nope.0
-
But net forces must be equal for constant velocity in the Y direction, or it will accelerate or decellerate? Or have I mis read what you said?!0
-
what about the considerable effects of friction (both from tyres and air resistance)?
you could technically pedal it out though I suppose0 -
yeehaamcgee wrote:Who wants to see a quick sketch of the principle behind the transition that matches your trajectory at the point of contact?
Look, I'm not getting drawn back into this old part of the thread, as I think everyone was bored of it... but I don't think anyone misunderstand the concept, it's very simple.: Your original example was poorly phrased and open to (deliberate) misinterpretation, and I took advantage of that for a cheap laugh because that's the sort of dick I am- but you missed the joke. But then rather than listening to me, you continued to ignore what I was actually saying, then turned to insults...
Now. I'm only posting this now, because you're still coming out with patronising slights and insults even 4 pages later, and it's spoiling the thread a bit...
Now, I'm going to take my life in my own hands, and respond to one of your posts. Brace yourselves Uncompromising extremist0 -
yeehaamcgee wrote:Right, regarding the original question, how about this explanation to clarify why rear wheel first landings are better.
if you stand on a 4 foot high wall and simply step off, landing vertically with your legs straight you'll feel a hell of an impact on your legs and feet because you just fell 4 feet.
Now (if you can still walk) try the same, but this time, sit on your bum, with your legs dangling over the edge before sliding off. This time your feet have dropped far less, since they were lower to the ground to start with. The impact is far less, and you should feel little or no discomfort on landing.
The rear-wheel landing on a bike is similar to the second drop, since you're extending your legs to meet the ground, and therefore reducing the height dropped. Your rear wheel will meet the ground much sooner, meaning you gain less acceleration from falling.
How does that strike people? make sense?
:
No. Because the argument you've put forward isn't exclusive to rear wheel landings, it works exactly the same for front wheel and 2-wheel landings! The physics is correct but the logic is false, the example works but it doesn't prove what you say it does.Uncompromising extremist0
