Newton's Third Law Explained: Is it for Cushions?

In summary, the conversation discusses the application of Newton's third law when punching a soft cushion. It is explained that the law still applies, but the force applied by the cushion is lower due to the longer stopping distance compared to a wall. The formula for calculating force and the process for posting a new thread on the forum are also mentioned.
  • #1
spectrum123
19
0
Please anybody explain me ... if i punch a soft cushion hardly say "F" force will thw cusion hurt me with the same ... every body says "NO" ok all right everybody says "you, in this case have not applied the "F" force because most part of it is wasted in changing the shape of cusion " so here comes the question what happens with the Newtons third law?
is it not meant for the things like cushion??
please explain ??
 
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  • #2
spectrum123 said:
Please anybody explain me ... if i punch a soft cushion hardly say "F" force will thw cusion hurt me with the same ... every body says "NO" ok all right everybody says "you, in this case have not applied the "F" force because most part of it is wasted in changing the shape of cusion " so here comes the question what happens with the Newtons third law?
is it not meant for the things like cushion??
please explain ??
Newton's 3rd law applies just fine. Since the pillow is light and soft, you simply cannot punch it hard. But whatever force you do manage to exert on it, the pillow will exert an equal and opposite force on you.
 
  • #3
When you punch something you initially accelerate your hand and arm to a velocity. Let's call that Vpunch. When it hits the object your hand and arm have to decelerate from Vpunch to zero again.

If you know the stopping distance "s" you can can apply the equation of motion

V^2=U^2 + 2as

to work out the deceleration "a".

Then if you know the mass of your hand and arm "m" you can work out the force the object needs to apply to your hand and arm to slow it down using

F=ma

The stopping distance "s" for a cushion is much longer than that of a wall. Than means "a" and "F" is lower for a cushion than a wall.

Doc Al is also correct. Newtons law means that at all times the force your hand applies to the object is the same as that which the object applies to your hand.
 
Last edited:
  • #4
thank i got it. "Cwattera and Doc al"
 
  • #5
please tell me how can i post a new threat ...i am new for this site please help...
 
  • #6
spectrum123 said:
please tell me how can i post a new threat ...i am new for this site please help...
Check out our Physicsforums FAQ.
 
  • #7
ok now i got it thanks
 

FAQ: Newton's Third Law Explained: Is it for Cushions?

What is Newton's Third Law?

Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that when two objects interact, they exert equal and opposite forces on each other.

How does Newton's Third Law apply to cushions?

Newton's Third Law applies to cushions because when you sit or lie on a cushion, the cushion exerts an upward force on you, known as the reaction force. This force is equal and opposite to your weight pushing down on the cushion, known as the action force.

Why does sitting on a cushion feel comfortable?

When you sit on a cushion, your weight pushes down on the cushion, causing it to compress. This compression creates a reaction force that pushes back up on you, providing support and making you feel comfortable.

Can Newton's Third Law explain why cushions lose their shape over time?

Yes, Newton's Third Law can explain why cushions lose their shape over time. As you sit on a cushion, the cushion exerts a reaction force on you, but you also exert a reaction force on the cushion. Over time, these repeated forces can cause the cushion to lose its shape and become flattened.

Does Newton's Third Law only apply to cushions?

No, Newton's Third Law applies to all objects and interactions. It is a fundamental law of physics that governs the motion of objects and the forces between them.

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