So, because I'm a hardcore person, I risked all this afternoon by going out in the wind, the rain and the cold to construct a willow den.
Yes, it seems a menial task, but it was actually quite thought-provoking: some pieces of willow were harder to push into the ground than others, and to try and force them in I'd sometimes end up hanging off of them, but other times I'd just push with all my strength, placing my body above the hole and pushing down, my feet still firmly planted on the ground.
Now, I was wondering, which of these two methods is better for sticking the stick into the ground? Ignoring the fact that by hanging from it, it is likely to topple, which method help me be more efficient in my future den-building exploits?
In other words, can you ever exert more downwards force than your weight? If so, then I'm guessing pushing down would be the better method, and if not, then hanging from the stick, putting all your weight into it, would exert the most possible downwards force.
Here's what a willow den looks like:
(source: raisingsparks.com)
Best Answer
The force you can exert is your mass times your acceleration. By the equivalence principle, just standing still is equivalent to accelerating at 9.8 m/s2, which is where the force of your weight comes from when you just stand still. But it is easy to accelerate more - like when you jump.
The force is only limited by your ability to push yourself off (transfer force to) the willow shoot. Imagine that you lie down next to the shoot, holding it in both hands. If you now pulled yourself up rapidly (the way some circus acrobats can pull themselves up a rope while appearing to hang horizontally) then you apply all your weight to the willow - and if you are strong enough to accelerate yourself while doing this, you could apply a force greater than your weight.
However, as you probably realize, there are other far more effective means to drive a stick into the ground. The key is to convert momentum into force - the equation is
$$m\Delta v = F \Delta t$$
This equation tells us that the change in momentum ($\Delta(mv) = m\Delta v$) is determined by the integral of force and time ($\int F\cdot dt=F\Delta t$ if F is constant). This is a direct consequence of the equation $F=ma$, which you can integrate with respect to time to get $\int F\cdot dt = \int m\ a\ dt = m \Delta v$.
When you use a hammer etc, you give it momentum during a long swing (small F, large t); but it slows down and comes to a stop in a very short interval, meaning that for that short time the force is much greater. A post driver is the tool people use to try to replicate this on the scale of large sticks being driven into the ground (hard to hammer the top of a tall thin stick). It may not be possible to use in your particular situation - but in general, it will allow you to apply a force much greater than your weight (bot for a shorter time). This is also the principle behind pile drivers etc . All these methods require the object to be driven to be strong enough to support the force you use to drive them into the ground...