A theoretical question about forces

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SUMMARY

The discussion centers on the physics of force and motion, specifically analyzing the scenario of a person lying on a bed being impacted by a knee. It concludes that the force exerted on the person's head when struck directly by the knee differs significantly from the force experienced when the knee impacts the bed's edge. The principles of Newton's second law (F=ma) are applied, highlighting that the mass of the objects involved affects the resulting acceleration. The analogy of pulling a tablecloth from under a plate is used to illustrate the differences in force and acceleration in these scenarios.

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freexd
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Hello,

Imagine the following scenario: a person is lying in bed, straight on the back. A second person passes the bed and accidently hits the edge with it's knee. The created force results in a fast head movement of the person on the bed, towards the direction where the impact was.

Is it correct that the force would have been the same high, when the knee hit the head directly?
 
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freexd said:
The created force results in a fast head movement of the person on the bed, towards the direction where the impact was.

I'm assuming there's a headboard, and in such a case it is the headboard that moves towards the person's head. This exerts a force on the head opposite of the direction of impact.
 
No, it' not correct. Supposing the bed was like a clean table with some kind of oil to eliminate the friction between the body on it and the bed the force on the head is going to be close to zero or zero (idealy).
 
freexd said:
Is it correct that the force would have been the same high, when the knee hit the head directly?

No. Consider the trick where you pull a table cloth from under a plate. The plate does not accelerate as quickly as the cloth. The forces could be very different.
 
F=ma, in the two cases the mass is different, the force is the same, so you would get a different acceleration.
 

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