Net Force (Pushing Boxes)

In summary, the student is pushing two boxes, one of which is heavier than the other. The net force on the box that is heavier is larger and points in the direction the boxes are traveling.
  • #1
AZNathanielC
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So, I am having some trouble with understanding force concepts. I do understand that Newton's 3rd law can be described as "describing the same interaction with the same magnitude of force, but in opposite directions on each object." So, I have a concern with a question that I have on my homework.

"A student pushes horizontally on two boxes. The boxes are moving to the right at a constant velocity. Box 1 has more mass than Box 2. There is friction between the boxes and the table."

The first question in regards to the situation, was...

"For a situation in which the boxes would be slowing down, which of the following statements is true about the magnitude of the forces?"

Out of the multiple choices I had, it was clear to me that the following answer was true:

"The magnitude of the force that box 1 exerts on box 2 is equal to the force that box 2 exerts on box 1." - This is due to Newton's 3rd law.

However, I have a question in regards to net force. The next question was asking, in the same situation where the boxes are slowing down, which box has the larger net force and which direction is the net force in? I am confused on the difference between net force and the magnitude of the force. If the magnitude of the force is the same between both objects in the interaction, what exactly is the net force and how is it different than the magnitude of the force?EDIT: Box 1 is behind Box 2
 
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  • #2
Net force just involves all of the forces acting on an object. For the first question you answered, you're just dealing with the forces that the boxes exert on each other, but the net force for each box may be different if other forces are involved. So, with this in mind, what would the net forces be on each box?
 
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  • #3
Ok, that makes sense. Well, I wasn't given any specific values for anything. However, based on what you just told me, wouldn't the net force on Box 1 be larger than the net force on Box 2 due to it's larger mass? This net force would be pointing to the right, which is the direction the boxes were traveling, correct?
 
  • #4
AZNathanielC said:
Ok, that makes sense. Well, I wasn't given any specific values for anything. However, based on what you just told me, wouldn't the net force on Box 1 be larger than the net force on Box 2 due to it's larger mass? This net force would be pointing to the right, which is the direction the boxes were traveling, correct?

The details of the problem are not all that clear -- at least not to me.

Does the student push on one of the boxes, which in turn pushes the other? If so, which box is pushed directly by the student?

Otherwise , what is the situation here?
 
  • #5
Box 1 is in contact with, but behind, Box 2. So, the student has contact with Box 1. The student pushes the boxes (they were already together when they were pushed).
 
  • #6
AZNathanielC said:
... wouldn't the net force on Box 1 be larger than the net force on Box 2 due to it's larger mass? This net force would be pointing to the right, which is the direction the boxes were traveling, correct?

What direction is the acceleration of Box 1?

What does Newton's 2nd Law say about net force and acceleration?
 
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  • #7
The direction of acceleration of Box 1 is to the right (which I am going to make an assumption is the positive direction, I should've made that assumption in my original post).

Newton's 2nd Law states that net force and acceleration must be in the same direction.
 
  • #8
AZNathanielC said:
The direction of acceleration of Box 1 is to the right (which I am going to make an assumption is the positive direction, I should've made that assumption in my original post).

Newton's 2nd Law states that net force and acceleration must be in the same direction.
Aren't the boxes slowing down as they move to the right?
 
  • #9
SammyS said:
Aren't the boxes slowing down as they move to the right?

Oh, correct. So there is a negative acceleration, my apologies.
 
  • #10
SammyS said:
Aren't the boxes slowing down as they move to the right?

Isn't the student pushing the box?If so,it will not slow down
 
  • #11
The problem says there's friction on the table too though, so in this case the friction would have to be greater than the applied force.
 
  • #12
adjacent said:
Isn't the student pushing the box?If so,it will not slow down

The problem does state that the student is pushing the boxes, however it doesn't state whether he continues to do so. It just asks, in the event that the boxes are slowing down when moving to the right, which net force is greater and in which direction is that net force pointing.

When working the problem, I just assumed that the student stopped applying force to the boxes, which resulted in the slowing down.
 
  • #13
adjacent said:
Isn't the student pushing the box?If so,it will not slow down
We are not told what set the boxes in motion in the first place. The boxes may have been moving already when the student started pushing, so may be slowing down despite a constant push.
 

1. What is Net Force?

Net Force refers to the overall force acting on an object, taking into account both magnitude and direction. It is the sum of all the individual forces acting on an object.

2. How is Net Force calculated?

To calculate Net Force, you must first determine all the individual forces acting on an object and their directions. Then, you can use vector addition to find the sum of these forces, taking into account both magnitude and direction.

3. What is the relationship between Net Force and acceleration?

According to Newton's Second Law, the acceleration of an object is directly proportional to the Net Force acting on it and inversely proportional to its mass. This means that a larger Net Force will result in a greater acceleration, while a smaller Net Force will result in a smaller acceleration.

4. How does Net Force affect an object's motion?

Net Force is directly related to an object's acceleration, which in turn affects its motion. If the Net Force is greater than zero, the object will accelerate in the direction of the force. If the Net Force is equal to zero, the object will maintain a constant velocity, and if the Net Force is less than zero, the object will decelerate or change direction.

5. What happens if the Net Force acting on an object is zero?

If the Net Force is zero, the object will maintain a constant velocity or remain at rest if it was already stationary. This is because the forces acting on the object are balanced, and there is no overall force causing a change in motion.

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