Actual value of normal reaction

In summary, the conversation discusses a high school student's question about atmospheric pressure. The student is trying to determine the normal reaction force acting on a cube block with a volume of 1 m3 and a top surface area of 1 m2, which has a mass of 1 kg. Through calculating the net force and taking into account atmospheric pressure, the student arrives at a large reading of 101009.81 N. The concept of buoyancy is mentioned, but it is not covered in the student's syllabus. The conversation also touches on the principle of pressure balance and the possibility of the force being adjusted. Overall, it is confirmed that atmospheric pressure does indeed exert a significant force on the block.
  • #1
Wong Tak
4
0
I am a high school student in Hong Kong studying Physics. I am having some problems about atmospheric pressure. Imagine there is a cube block with volume 1 m3 and top surface area 1 m2 . The cube block is being placed on the floor and it has mass of 1 kg. What is the normal reaction force F acting on the block by the floor?
Considering the free body diagram of the block, there are effectively three forces acting on it . They're the weight , F , and the force based on the atmospheric pressure on the top surface. ( Since the side surface's force canceled out each other , they're neglected) Since net force= 0 , F = mg + Area of top surface x atmospheric pressure= 1x9.81 + 1x101x1000 =101009.81 N. Is it really that large? Or my calculation is wrong? My teacher said that it includes a concept called buoyancy in this situation and it is out of our syllabus. Can anyone explain it to me ? Another alternative question I have is that what is the principle of the pressure balance ? Doesn't it measure the normal reaction force acting on it? I mean even if I didn't step on it , it should still have a large reading , right ? Or is it adjusted ? Thanks
 
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  • #2
Yes, atmospheric pressure really does exert that great a force on the block. But it is not easy to make an 'air-tight' seal between block and surface, so usually that force is balanced (except for the small buoyant force).
 

What is the normal reaction?

The normal reaction is the force exerted by a surface on an object in contact with it, perpendicular to the surface. It is also known as the normal force or contact force.

How is the normal reaction calculated?

The normal reaction is calculated using Newton's third law of motion, which states that every action has an equal and opposite reaction. In the case of the normal reaction, the force exerted by the surface on the object is equal in magnitude and opposite in direction to the force exerted by the object on the surface.

What factors affect the normal reaction?

The normal reaction is affected by the mass of the object, the force of gravity, and the angle of the surface. The normal reaction will increase with an increase in mass or force of gravity, and will decrease with an increase in the angle of the surface.

Why is the normal reaction important?

The normal reaction is important because it is essential for an object to remain stationary or in motion on a surface. It also helps to prevent objects from passing through each other when in contact.

Can the normal reaction be negative?

Yes, the normal reaction can be negative if the force exerted by the object on the surface is greater than the force exerted by the surface on the object. This can happen in situations where the object is applying a downward force on the surface, such as when a heavy object is placed on a spring.

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