>> If the 1000 N force is on an object weighing 1000 kg, and the 1 N force 
>> is on an object weighting 1 kg, then yes, they both require the same 
>> amount of friction and will result in the same acceleration.
>
> This must truly be the definition of "counter-intuitive". I cannot begin 
> to imagine how this can be true. It is surely self-evident that applying a 
> large force requires better grip than does applying a small force.

Not if the contact force is proportionally higher.

Press your thumb and finger together very lightly and see how much sideways 
force you need to slide them across each other.  Now press them together 
much harder and you'll find you need a much bigger sideways force to 
overcome the friction.

It's the same with a 1000 kg car and a 10 kg animal, because the car is 
pushing down on the road 100 times more than the animal it can generate 100 
times more forward force before slipping.

http://en.wikipedia.org/wiki/Friction

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