# Calculating the Resultant Force on a Gate - Is No Force at B Possible?

• eurekameh
In summary, the conversation discusses the resultant force on a gate and the possibility of there being no force acting on the stop at point B. One person suggests that if b is large enough, there could be a counterclockwise torque around point A, but another person argues that there must be a reaction force at B to balance the force equation. They also mention the absence of a vertical force on the horizontal part of the gate and the physical implications of removing the stop at B. Finally, they discuss the direction of the force at B and suggest adding reaction components at point A for completeness on the diagram.

#### eurekameh

I've figured out the resultant force on the gate by adding the magnitudes of F1, F2, and F3. However, I'm trying to figure out the distance b such that there is absolutely no force acting on the stop at point B. Is this even possible? It seems like it isn't, since all forces are pointing to the left and there has to always be a reaction force at B.

I've never done a fluid statics course but F2 appears to have a vertical component as drawn. Why can't that produce an anticlockwise torque around "a" if "b" is large enough?

Isn't there a missing vertical force on the horizontal part of the gate?

Yes, if b is large enough, there would be a counterclockwise torque around A. The moment equation balances out, but these forces would still all be pointing to the left. I think there has to be a reaction force at B to balance the Force equation in the x direction.
And yeah, I'm missing a vertical force on on the horizontal part of the gate.

I mean, let's forget the math. If you think physically about the problem, I think that if you remove the stop at B, the gate would open, even if b was immensely large.

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So, what is the direction of the force at B. Put it on the diagram. Then also add the reaction components at A, for completeness.

I understand your curiosity about the possibility of no force at point B. However, based on the information provided, it is not possible for there to be no force at point B. This is because of the fundamental law of Newton's third law, which states that for every action, there is an equal and opposite reaction.

In this scenario, the forces F1, F2, and F3 are acting on the gate in different directions, but they are all pointing to the left. This means that there will always be a reaction force at point B, even if it is not directly in line with the other forces.

To further understand this concept, we can use the concept of vector addition. When adding vectors, the resultant force is the combination of all the individual forces acting on the object. In this case, the resultant force would still be pointing to the left, even if it is not directly in line with the other forces. This is because the resultant force takes into account the magnitude and direction of all the forces acting on the object.

In conclusion, based on the laws of physics, it is not possible for there to be no force at point B. There will always be a reaction force present, even if it is not directly in line with the other forces. I hope this explanation helps clarify any confusion.

## 1. What is the formula for calculating the resultant force on a gate?

The formula for calculating the resultant force on a gate is R = F1 + F2 + F3 + ... + Fn, where R is the resultant force and F1, F2, F3, etc. are the individual forces acting on the gate.

## 2. How do I determine the direction of the resultant force on a gate?

The direction of the resultant force on a gate can be determined by using the Right Hand Rule. Point your fingers in the direction of the first force and then curl them towards the direction of the second force. The resultant force will be in the direction of your thumb.

## 3. What is the significance of having no force at point B?

No force at point B means that the gate is in a state of equilibrium, where the forces acting on it cancel each other out. This can occur if the forces are equal in magnitude and opposite in direction, or if there are no forces acting on the gate at all.

## 4. How is the magnitude of the resultant force affected when the angle between forces changes?

The magnitude of the resultant force is affected by the angle between forces through the use of trigonometric functions. As the angle between forces increases, the magnitude of the resultant force decreases.

## 5. Can the resultant force on a gate ever be negative?

No, the resultant force on a gate cannot be negative. Force is a vector quantity, meaning it has both magnitude and direction. A negative force would imply a direction opposite to the one specified, which is not possible in the context of calculating resultant forces.