# When would the normal force not equal the weight?

• gungo
In summary, the normal force between two surfaces is always perpendicular to the contact plane and is the minimum force required to prevent interpenetration. In certain situations, such as on a frictionless slope or when there are multiple objects stacked on top of each other, the normal force may not equal the weight of the object due to additional forces acting in the y-direction.
gungo

## Homework Statement

I know that on a horizontal surface. if the net force is 0 in the y direction the weight of object=the normal force, but wouldn't the normal force always equal the magnitude of gravity on an object, just in opposite directions? Because if the weight is stronger than the normal force or vice versa, the object would move in the y direction, but objects don't fall through the ground or randomly or start floating so I'm kind of confused.

Fg=mg

## The Attempt at a Solution

N/A

Assuming a statics situation ##\sum \mathbf F = 0##, there are conceivable situations in which the normal force wouldn't equal the force of gravity. One example is if you were applying a light upward force on the object from a hand or string or something that isn't strong enough to actually pick it up. In this case, the normal force would equal the force of gravity minus the applied upward force.

gungo said:

## Homework Statement

I know that on a horizontal surface. if the net force is 0 in the y direction the weight of object=the normal force, but wouldn't the normal force always equal the magnitude of gravity on an object, just in opposite directions? Because if the weight is stronger than the normal force or vice versa, the object would move in the y direction, but objects don't fall through the ground or randomly or start floating so I'm kind of confused.

Fg=mg

## The Attempt at a Solution

N/A
Normal force between two surfaces is the minimum magnitude force which prevents their interpenetration. Thus, it is always normal to the contact plane.
If an object is placed on a frictionless slope, the normal force only has to counter the component of gravity normal to the plane. The other component leads the object to slide down.

conscience

## 1. When would the normal force not equal the weight?

The normal force would not equal the weight when an object is accelerating or decelerating. This is because the normal force is the force exerted by a surface on an object to prevent it from sinking into the surface, and it only equals the weight when the object is at rest or moving at a constant velocity.

## 2. Does the normal force always act in the opposite direction of the weight?

No, the normal force can act in any direction perpendicular to the surface. It is only equal in magnitude to the weight when the object is at rest or moving at a constant velocity.

## 3. Can the normal force be greater than the weight?

Yes, the normal force can be greater than the weight when an object is experiencing a net upward force, such as when it is being pushed or lifted from below. In this case, the normal force would be equal to the sum of the weight and the upward force.

## 4. What is the relationship between the normal force and the weight?

The normal force and the weight are directly proportional to each other. If the weight of an object increases, the normal force will also increase in order to prevent the object from sinking into the surface.

## 5. How is the normal force calculated?

The normal force is calculated by multiplying the mass of an object by the acceleration due to gravity (9.8 m/s^2). This will give the weight of the object, which is equal to the magnitude of the normal force when the object is at rest or moving at a constant velocity.

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