# The Naked Scientists Forum

### Author Topic: how much pressure is exerted on a bike when it impacts the ground(jumping)?  (Read 1853 times)

#### alicjhns3

• First timers
• Posts: 1
##### how much pressure is exerted on a bike when it impacts the ground(jumping)?
« on: 16/01/2010 22:07:03 »
?Trying to calculate the pressure on a bike when you jump a ramp ect.

#### Karsten

• Hero Member
• Posts: 701
##### how much pressure is exerted on a bike when it impacts the ground(jumping)?
« Reply #1 on: 16/01/2010 23:03:11 »
I could not help you with the calculation but I do know that to calculate one needs numbers. So, you need to put some numbers here. Speed, angle of ramp, mass or rider and bike, etc. A sketch would help too.

#### Geezer

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• "Vive la résistance!"
##### how much pressure is exerted on a bike when it impacts the ground(jumping)?
« Reply #2 on: 17/01/2010 00:55:12 »
?Trying to calculate the pressure on a bike when you jump a ramp ect.

Assuming the bike lands on a horizontal surface, we can make a fairly good estimate if we know the vertical distance from the apex of the jump to the point of contact. If we know that distance (s), the vertical velocity (v) at impact is given by:

v = √(2gs)  where g is the acceleration due to gravity.

If we know the mass of the bike and rider, we can estimate the force based on some assumptions about how quickly the combined mass decelerated, and from that calculate various pressures.

It gets quite a bit more complicated if the bike lands on a downslope. In that situation, we do need to know the forward velocity of the bike and the incline of the landing ramp. Those factors can make an enormous difference. If they are set up "just right" the bike can land with almost no impact at all. This probably explains why most daredevil jumpers never land on a horizontal surface

#### Bored chemist

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##### how much pressure is exerted on a bike when it impacts the ground(jumping)?
« Reply #3 on: 17/01/2010 13:30:56 »
To a good aproximation (ie ignoring air resistance) the calculation is quite easy.
The accelaration (upwards) as you hit the ground is g multiplied by the distance you fall, divided by the distance over which you stop.
the foce is that accelaration times the mass.
So if you fall from a peak height of 1 metre and come to rest in 0.1m the accelaration is 10g.
If you weigh 70 Kg then the force is about 7KN.
The tricky bit is working out over what distance you stop.
How far does your centre of gravity (roughly the middle of your belly) move from when you first touch the ground till you have stopped moving downwards?

#### The Naked Scientists Forum

##### how much pressure is exerted on a bike when it impacts the ground(jumping)?
« Reply #3 on: 17/01/2010 13:30:56 »