Newtons third law and elevators

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SUMMARY

The discussion centers on the application of Newton's third law in the context of two objects stacked in an accelerating elevator. The normal force acting on the top object is equal and opposite to the contact force exerted by the bottom object. The total force experienced by the top object includes both gravitational force and the force due to the elevator's acceleration. This analysis involves understanding the interactions among the earth, elevator, and the two objects within it.

PREREQUISITES
  • Understanding of Newton's third law of motion
  • Familiarity with gravitational force concepts
  • Basic knowledge of contact forces
  • Awareness of classical physics principles
NEXT STEPS
  • Study the implications of Newton's third law in various physical systems
  • Explore the effects of acceleration on forces in different contexts
  • Learn about gravitational force calculations in varying scenarios
  • Investigate the relationship between mass, weight, and normal force
USEFUL FOR

Students of physics, educators teaching classical mechanics, and anyone interested in understanding force interactions in dynamic systems such as elevators.

kthejohnster
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If two objects are stacked in an accelerating elevator what is the force equal and opposite to the normal force on the top object?

I was thinking that it has to be either the force of gravity or contact force between the two objects could it be anything else?
 
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kthejohnster said:
If two objects are stacked in an accelerating elevator what is the force equal and opposite to the normal force on the top object?

I was thinking that it has to be either the force of gravity or contact force between the two objects could it be anything else?

Hi welcome to physicforums. :smile:

Here you are dealing with four (or even five) objects: the earth, the elevator (and the cable that holds it up) and two objects inside the elevator. The force of gravity, using classical physics, is pulling on he elevator and the two objects.

Newton's third law applies to all force pairs. In this case you can just focus on the force pair [top object] <-> [bottom object]. The force that is felt by the top object is the contact force from the bottom object; inversely the bottom object feels the same force (but of course in opposite direction) from the top object at its top surface.

The magnitude is equal to the force from gravitation plus the force from acceleration.

See also https://www.physicsforums.com/showthread.php?t=250895
 

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