When normal force isn't normal l

[Gersty]

When normal force isn't "normal"l

Homework Statement

A box with a certain mass is pulled across a horizontal surface by a rope at an angle. Figure out the components, the friction, the acceleration of the box, when the tension in the rope, its angle, the mass of the box, and mu are given.

Homework Equations

F=ma, sin (theta) hypotenuse, etc...

The Attempt at a Solution

I understand the solution but I'm having trouble explaining how the normal force is found. I am used to calculating the using m(g) to calculate the force of gravity. It seems as though the normal force should just be the same as gravity plus the upward component of the rope. I get that equilibrium plays a role but am just having difficulty explaining it.

 

[ehild]

Homework Statement

A box with a certain mass is pulled across a horizontal surface by a rope at an angle. Figure out the components, the friction, the acceleration of the box, when the tension in the rope, its angle, the mass of the box, and mu are given.

Homework Equations

F=ma, sin (theta) hypotenuse, etc...

The Attempt at a Solution

I understand the solution but I'm having trouble explaining how the normal force is found. I am used to calculating the using m(g) to calculate the force of gravity. It seems as though the normal force should just be the same as gravity plus the upward component of the rope. I get that equilibrium plays a role but am just having difficulty explaining it.

What do you mean with the sentence "It seems as though the normal force should just be the same as gravity plus the upward component of the rope."? The rope has no "upward component". In what direction is the rope pulled?

ehild

 

[SteamKing]

Imagine a box of mass 'm' just sitting on the ground. What is the normal force exerted by the ground on the box?

Now, imagine the box has a rope tied to it. Does the normal force on the box change?

If you pull straight up on the rope so that there is a tension of 5 N and the box is still sitting on the ground, what is the normal force exerted by the ground on the box? If the tension is 10 N? When is the normal force = 0?

 

[HallsofIvy]

Homework Statement

A box with a certain mass is pulled across a horizontal surface by a rope at an angle. Figure out the components, the friction, the acceleration of the box, when the tension in the rope, its angle, the mass of the box, and mu are given.

If the rope makes angle [itex]\theta[/itex] with the horizontal and has tension T, then the "upward force" is [itex]Tsin(\theta)[/itex] and the horizontal force is [itex]Tcos(\theta)[/itex]. The "normal force" (normal to the surface) is the weight of the box, mg, minus that upward force: [itex]mg- Tsin(\theta)[/itex].

 

[Nickie]

I would like to clarify that the term "normal force" is often used in physics to describe the perpendicular force exerted by a surface on an object in contact with it. This force is typically equal in magnitude and opposite in direction to the force of gravity on the object. However, in certain situations, such as when an object is pulled at an angle by a rope, the normal force may not be "normal" in the traditional sense.

In this scenario, the normal force is still present and is still equal to the force of gravity on the object, but it may not be the only force acting on the object. The tension force from the rope, which is pulling the object at an angle, also contributes to the overall force on the object. This means that the normal force may not be the only force balancing out the force of gravity, and the resulting acceleration of the object may be influenced by both the normal force and the tension force from the rope.

To calculate the normal force in this situation, one must consider the vector components of the forces acting on the object. The vertical component of the tension force can be added to the force of gravity to determine the magnitude of the normal force, while the horizontal component of the tension force can be used to determine the acceleration of the object in that direction.

In summary, the normal force may not always be "normal" in the traditional sense, but it is still an important force to consider in situations where an object is being pulled or pushed at an angle. Its magnitude and direction can be determined by considering all the forces acting on the object and using vector analysis to determine the resulting acceleration.