- #1
Thoams Jerome
Sounds wird but I tried it and people use this it help clime walls. How does this happen?
sophiecentaur said:I think it works because the pressure against the wall, due to your rapid horizontal deceleration allows you to provide a lot of downwards friction force (without hitting the wall hard, you feet would just slip downwards). There is another factor, too. By virtue of the fact that your foot doesn't slip down the wall you can transfer some of your Kinetic Energy to Gravitational Potential Energy (taking you higher) in the same way that a pole vaulter uses the pole or as you can hit a steep ramp on a bike. That will 'feel' like an upwards push due to the free energy.
Starting with initial KE = final GPE (and that is the maximum, not allowing for loss)Thoams Jerome said:Do you know were I find the equation for the kinetic to gravitational energy
Thoams Jerome said:Do you know were I find the equation for the kinetic to gravitational energy? I saw some one doing this, So I'm trying to find a way to take two steps up a wall instead of one. I needed to know if it was friction or something else at play thank you.
That's not consistent with rest of your post. The friction force is very much dependent on the retarding force, of course, but the KE is very relevant and can be used if you 'get the angles right'.Mister T said:It's entirely friction. Looking at the energy instead of the force doesn't change this, it's simply another way of looking at the situation.
The friction force is an upward force on your body, which causes an upward acceleration. This allows you to convert the kinetic energy you gained during the acceleration to potential energy.
sophiecentaur said:Once your forward speed has been lost, and the normal force on the wall has dropped to zero,[...]
[...]you have no traction but KE can take you higher than that point.
I think we are actually singing from the same hymn sheet and that actually both friction and energy need to be considered in the context of the 'trick'.Mister T said:By that time you have used the friction force to accelerate yourself upward, so you now have some upward speed.
Yes, because you have some upward speed.
There is more to it than that. By running at the wall, you have Momentum and time for which you can exert a force can be much greater than with a standing start. The Change of Momentum is equal to the Impulse (=Force X time). Initially, your leg is bending, reducing your momentum and applying the necessary force to provide friction. If the contact point with the wall is below the level of your Centre of Mass there will be a vertical component of force which will push you upwards even if you don't attempt to climb.Khashishi said:By kicking a wall, you provide a normal force and a downward force on the wall.
sophiecentaur said:I think we are actually singing from the same hymn sheet and that actually both friction and energy need to be considered in the context of the 'trick'.
Khashishi said:By kicking a wall, you provide a normal force and a downward force on the wall. If the downward force is lower than the static friction, then you will grip to the wall, and you can push yourself up. Otherwise, you will slip, but still accelerate up a little bit due to dynamic friction, which is lower than static friction.
The justification for equating PE with KE seems to be that one can strike the wall with the feet in an elastic collision without slipping. Both suppositions are questionable, but reasonably close.sophiecentaur said:Starting with initial KE = final GPE (and that is the maximum, not allowing for loss)
KE = mv2/2
PE = mgh
So you can equate those two and m cancels out, giving you
h = v2/2g
jbriggs444 said:The justification for equating PE with KE seems to be that one can strike the wall with the feet in an elastic collision without slipping. Both suppositions are questionable, but reasonably close.
[Imagine a stiff but perfectly elastic pogo stick hitting the wall at a 45 degree angle without slipping]
CWatters said:The reaction force where a foot meets the wall will contain components due to friction and the normal force.
Well, I was imagining the person as being passive so that "elastic" is the best collision you can get. I think that is what you were getting at with the "particle" characterization.Mister T said:If you model the person as a particle, yes.
Yes, I agree that one can do better than elastic with an appropriate active mechanism such as a jumper or a pre-stressed pogo stick.Mister T said:With the pogo stick spring originally compressed somewhat
sophiecentaur said:Starting with initial KE = final GPE (and that is the maximum, not allowing for loss)
KE = mv2/2
PE = mgh
So you can equate those two and m cancels out, giving you
h = v2/2g
But that value of h will be pretty optimistic.
Without the friction, you couldn't push down.[/QUO
thank you
jbriggs444 said:Well, I was imagining the person as being passive so that "elastic" is the best collision you can get. I think that is what you were getting at with the "particle" characterization.
And yet we are willing to contemplate elastic collisions between pointlike particles. There is something not completely realistic in that idealization.Mister T said:Yes. Having no internal structure, a particle is not capable of storing (or releasing) internal energy.
Haha. Mine's older than yours.jbriggs444 said:With my legs and age,
That sounds reasonable. it would rely on the performer using just the right amount of normal force by controlling the leg - but it would also rely on energy conservation, which doesn't apply to muscles. OTOH, the performer can put some energy in during the manoeuvre. It gets too hard to make a good prediction.jbriggs444 said:A conservation of momentum argument indicates that vertical impulse is limited to μμ\mu times horizontal impulse where μμ\mu is the coefficient of static friction.
The particle model can't deal with the necessary geometry for achieving the upwards result. You have to use a model with a finite size, I think. It would be one step too far in idealising the situation.Mister T said:If you model the person as a particle, yes.
When you run and kick a wall, your foot exerts a force on the wall. According to Newton's third law of motion, the wall will exert an equal and opposite force on your foot. This force is what you feel as an upwards push.
The upwards force is caused by both the wall and your foot. Your foot exerts a force on the wall, causing it to push back and create an equal and opposite force on your foot.
Yes, the speed of your run does affect the upwards force. The faster you run and kick the wall, the greater the force your foot will exert on the wall and the greater the upwards force you will feel.
This is because when you kick with your toes, you are using a smaller surface area to exert the force on the wall. This concentrated force results in a stronger upwards push on your foot.
Yes, there is a potential danger in running and kicking a wall. The force exerted on your foot and the wall can cause injury if done with excessive force. It is important to be cautious and not to kick the wall too hard.