Solving Friction Problem: Box on Ground, Force Applied

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In summary, when a box is placed on the ground with a limiting static friction of 5N, an external force of 2N will result in a friction of 2N on the earth. The box and earth will either move together or the box will not move, depending on the net force. To cause relative movement between boxes, an external force greater than 10N will be needed. This is due to the resistance provided by static friction, which can only provide a maximum of 5N of force before slipping occurs.
  • #1
terence1732
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As follows,
a box is placed on the ground
And let the limiting static friction be 5N
for instance an external force 2N is applied to the box
Then, will the friction on the box be 2N?
if yes, then .. there will be a friction of 2N on the earth? causes they are action and rxn pair
And will the Earth move but the box will not move?

or will the box and the Earth just share the 2N force and move together? the friction between them is not exactly 2N but much smaller then it?
But, in this way, a much greater applied force (>5N) will be needed to cause relative movement

I just can't find out what i am missing.
Pls help thanks a lot
 
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  • #2
terence1732 said:
As follows,
a box is placed on the ground
And let the limiting static friction be 5N
for instance an external force 2N is applied to the box
Then, will the friction on the box be 2N?
Yes.
if yes, then .. there will be a friction of 2N on the earth? causes they are action and rxn pair
Yes.
And will the Earth move but the box will not move?

or will the box and the Earth just share the 2N force and move together? the friction between them is not exactly 2N but much smaller then it?
Whether the Earth accelerates or not depends on the net force. If the 2N force is external to the earth, then box and Earth will move together. Note that the acceleration will be miniscule, but it implies that the friction force on the box will be slightly less than 2N. (Newton's 2nd law.)
But, in this way, a much greater applied force (>5N) will be needed to cause relative movement
No, just a tiny bit greater than 5N. (Way too small to ever measure or notice! This is just a theoretical point.)
 
  • #3
Thank for your help
But now I hv another problem..
A case as follows,
Now I place a box (1kg) on the ground.
Assume there's no friction between the ground and this box.

And I place another box (also 1 kg) above this box
The limiting static friction between this two box is 5N

And now external force of 2N is applied to the lower box
Will they move together?
If yes, then the friction between the box surface should be 1N?

And I want to cause a relative movement between boxes,
should the external force be greater then 10N?

It seems that it is quite strange..
 
  • #4
terence1732 said:
And now external force of 2N is applied to the lower box
Will they move together?
If yes, then the friction between the box surface should be 1N?
Right. The surfaces will resist slipping until they reach the static friction limit. In this case only 1 N of friction is required, which is well within the limit.
And I want to cause a relative movement between boxes,
should the external force be greater then 10N?
Right. You need to create a situation where more force is required to accelerate the block than static friction can provide. In this case, that means an acceleration of 5 m/s^2, which requires a force of 10 N. (Once the upper block begins to slip, less force will be required to maintain slipping since static friction will be replaced by kinetic friction.)
It seems that it is quite strange..
Strange but true. :wink:
 

FAQ: Solving Friction Problem: Box on Ground, Force Applied

What is friction and why is it important to solve this problem?

Friction is a force that occurs when two surfaces come into contact and resist each other's motion. It is important to solve this problem because friction can greatly impact the movement of objects and can affect the accuracy of scientific experiments and the efficiency of mechanical systems.

How do you calculate the friction force in this problem?

The friction force can be calculated using the formula Ff = μN, where μ is the coefficient of friction and N is the normal force exerted by the surface on the object. In this problem, the normal force is equal to the weight of the box, and the coefficient of friction depends on the materials and surfaces in contact.

What are the factors that affect friction in this problem?

The factors that affect friction in this problem include the coefficient of friction, the weight of the box, and the type of surface the box is resting on. The angle of the applied force and any external forces acting on the box can also affect the friction force.

How can the friction problem be solved using Newton's laws?

Newton's first law states that an object in motion will remain in motion at a constant velocity unless acted upon by an external force. Therefore, to solve the friction problem, we must consider the external forces acting on the box, such as the applied force and the friction force, and apply Newton's second law (F=ma) to determine the acceleration of the box. We can then use this acceleration to solve for the final velocity and displacement of the box.

What are some real-life applications of solving friction problems?

Solving friction problems is important in many fields, such as engineering, physics, and materials science. It can be applied to designing efficient machines and reducing wear and tear on moving parts. In everyday life, understanding friction can help us improve our grip on objects, determine the best materials for different surfaces, and even explain how vehicles and planes move.

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