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Ok, umm these may sound like dumb questions, and I am sorry but here goes. (I think i have a lot of misconceptions)
1. If I push myself against a wall and exert a constant force, the wall will exert a reaction force against me and therefore net force = 0 and no motion. But if I throw myself against the wall, at the instant i hit the wall I'll be pushed back and likely fall over.
This is where I am kind of confused. Regardless of whether I'm applying a constant force or an instantaneous force, won't the reactionary force be the same and hence the net force = 0? Why is it for the latter I will tend to experience a force/acceleration away from the wall (the reactionary force), when it should have been canceled out by the initial force I exerted (i.e net force should be zero?)
2. I was hoping that someone could help me understand how deformations work. This is again related to my understanding of Newton's 3rd Law. Say I place a mass on a wooden plank, the plank will deform until it is bent to support the weight of the mass. Is it right to say that when I first place the mass on the plank, the plank is 'unable' to supply an equal reactionary force to the mass' weight, and hence has to bend until a point where the reaction force is equal to that of the weight?
How does the deformation of the plank in this case help to support the weight of the mass (I assume something to do with tension?), also (if I'm right) why is it that it is initially unable to supply an equal, opposite reaction force? Does this imply that Newton's 3rd Law only applies for 'hard' objects, or those that don't deform?
I'm also thinking that, if on the molecular level, at the point of contact between the mass and the plank, if all the forces on the molecules (I use this for lack of a better word) have equal and opposite reactionary forces, won't deformation not take place at all?
THANKS SO MUCH IN ADVANCE
1. If I push myself against a wall and exert a constant force, the wall will exert a reaction force against me and therefore net force = 0 and no motion. But if I throw myself against the wall, at the instant i hit the wall I'll be pushed back and likely fall over.
This is where I am kind of confused. Regardless of whether I'm applying a constant force or an instantaneous force, won't the reactionary force be the same and hence the net force = 0? Why is it for the latter I will tend to experience a force/acceleration away from the wall (the reactionary force), when it should have been canceled out by the initial force I exerted (i.e net force should be zero?)
2. I was hoping that someone could help me understand how deformations work. This is again related to my understanding of Newton's 3rd Law. Say I place a mass on a wooden plank, the plank will deform until it is bent to support the weight of the mass. Is it right to say that when I first place the mass on the plank, the plank is 'unable' to supply an equal reactionary force to the mass' weight, and hence has to bend until a point where the reaction force is equal to that of the weight?
How does the deformation of the plank in this case help to support the weight of the mass (I assume something to do with tension?), also (if I'm right) why is it that it is initially unable to supply an equal, opposite reaction force? Does this imply that Newton's 3rd Law only applies for 'hard' objects, or those that don't deform?
I'm also thinking that, if on the molecular level, at the point of contact between the mass and the plank, if all the forces on the molecules (I use this for lack of a better word) have equal and opposite reactionary forces, won't deformation not take place at all?
THANKS SO MUCH IN ADVANCE