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Action and Reaction
Storyboard 
Newton's third principle defines that forces have to be generated in pairs so that their sum is zero. This implies that before an action there is always a reaction of equal magnitude but in the opposite direction.
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Newton\'s Third Law
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The fact that every force exerted generates a reaction force is part of Newton\'s third law:
| $ F_R =- F_A $ |
One of the consequences is that you cannot exert a force on yourself because the reaction force cancels it out. An example of this is the impossibility of the so-called Münchhausen effect. It is said that Baron Münchhausen, at one point, found himself sinking in a swamp. In an attempt to save himself, the baron supposedly tried to pull himself up by his own hair, thus lifting himself and escaping the swamp.
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Boosting
Note
When a swimmer pushes off, she exerts a force of ERROR:9790.1 on the pool wall, which in turn generates a force of ERROR:9789.1 on her body, propelling her movement:
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Force on a wall
Quote
If we attempt to exert force against a wall, we will notice that the main limitation is determined by the adherence of our shoes to the floor. If the floor is smooth, we will typically begin to slip, thereby limiting the force we are capable of exerting.
It is interesting to note that if we push in a non-horizontal manner, the vertical component will affect our vertical force against the floor. In other words, the vertical reaction to our action against the wall will result in an increase (if we are pushing more upward) or a decrease (if we are pushing more downward) in our weight.
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Walking
Exercise
Every time we walk, we need to propel our body with each step. To do this, we place our foot on the ground, and assuming it doesn\'t slide due to friction, our muscles exert a force on our body that propels it forward and transfers the reaction to the foot, which in turn transmits it to the ground (the planet):
Since the planet is enormous, we don\'t directly observe the effect of this reaction. However, if we are standing on a smaller object like a cylinder, we can induce its rolling motion by moving relative to our position on the cylinder while it rolls in the opposite direction.
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Action and Reaction
Storyboard
Newton's third principle defines that forces have to be generated in pairs so that their sum is zero. This implies that before an action there is always a reaction of equal magnitude but in the opposite direction.
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As the momentum variation ($\Delta p$) is with the inertial Mass ($m_i$) and the speed Diference ($\Delta v$) equal to
for the case where mass is constant, the change in momentum can be written with the moment ($p$) and the initial moment ($p_0$), which, combined with the speed ($v$) and the initial Speed ($v_0$), yields
$\Delta p = p - p_0 = m_i v - m_i v_0 = m_i ( v - v_0 ) = m_i \Delta v$
where the speed Diference ($\Delta v$) is computed with:
thus resulting in
As the momentum variation ($\Delta p$) is with the inertial Mass ($m_i$) and the speed Diference ($\Delta v$) equal to
for the case where mass is constant, the change in momentum can be written with the moment ($p$) and the initial moment ($p_0$), which, combined with the speed ($v$) and the initial Speed ($v_0$), yields
$\Delta p = p - p_0 = m_i v - m_i v_0 = m_i ( v - v_0 ) = m_i \Delta v$
where the speed Diference ($\Delta v$) is computed with:
thus resulting in
Examples
When a swimmer pushes off, she exerts a force of ERROR:9790.1 on the pool wall, which in turn generates a force of ERROR:9789.1 on her body, propelling her movement:
If we attempt to exert force against a wall, we will notice that the main limitation is determined by the adherence of our shoes to the floor. If the floor is smooth, we will typically begin to slip, thereby limiting the force we are capable of exerting.
It is interesting to note that if we push in a non-horizontal manner, the vertical component will affect our vertical force against the floor. In other words, the vertical reaction to our action against the wall will result in an increase (if we are pushing more upward) or a decrease (if we are pushing more downward) in our weight.
Every time we walk, we need to propel our body with each step. To do this, we place our foot on the ground, and assuming it doesn\'t slide due to friction, our muscles exert a force on our body that propels it forward and transfers the reaction to the foot, which in turn transmits it to the ground (the planet):
Since the planet is enormous, we don\'t directly observe the effect of this reaction. However, if we are standing on a smaller object like a cylinder, we can induce its rolling motion by moving relative to our position on the cylinder while it rolls in the opposite direction.
An important aspect of force is that it cannot be created out of nothing. Every time we attempt to generate a action force ($F_A$) (an action), a reaction force ($F_R$) will inevitably be generated with the same magnitude but opposite direction:
In other words, forces always occur in pairs, and the sum of these pairs always equals zero.
The force ($F$) is defined as the momentum variation ($\Delta p$) by the time elapsed ($\Delta t$), which is defined by the relationship:
The force ($F$) is defined as the momentum variation ($\Delta p$) by the time elapsed ($\Delta t$), which is defined by the relationship:
In the case where the inertial Mass ($m_i$) is constant, the momentum variation ($\Delta p$) is proportional to the speed Diference ($\Delta v$):
In the case where the inertial Mass ($m_i$) is constant, the momentum variation ($\Delta p$) is proportional to the speed Diference ($\Delta v$):
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