# Rail Gun Problem: Force & Friction Analysis

• David112234
In summary, the rod will begin to move when the force of friction is equal to the force due to the magnetic field. While technically, if they are equal there will be no acceleration, in the real world there is always some noise that will cause the rod to begin to move. Therefore, setting them equal allows for the slightest increase in force to trigger movement.
David112234

F_f = Nu
F_B - IL x B

## The Attempt at a Solution

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Using the hint
"The rod will begin to move when the force of friction is equal to the force due to the magnetic field."
I was able to get the answer
But I don't understand why it is that way. In order make the rod move, wouldn't the force from the magnetic field have to be greater than the friction force? if they are equal than the net force is zero and there can not be an acceleration since F(net) = ma

Technically, you are right. If they are equal, there will be no acceleration. However, if the force increases beyond that by an infinitesimal amount, the rod will begin to move. That's why you set them equal.

David112234
TomHart said:
Technically, you are right. If they are equal, there will be no acceleration. However, if the force increases beyond that by an infinitesimal amount, the rod will begin to move. That's why you set them equal.
To add to that, in the real world there is always noise, such as vibrations, and exact equality is only a theoretical concept.
As soon as there is the slightest movement, kinetic friction applies, and that is nearly always less (certainly never more) than static friction.

David112234 and TomHart

## 1. What is a rail gun?

A rail gun is a type of electromagnetic weapon that uses electricity to accelerate projectiles at high speeds. It consists of two parallel rails, a power source, and a conductive projectile.

## 2. How does a rail gun work?

A rail gun works by using the principle of electromagnetic induction. When a high voltage is applied to the two parallel rails, it creates a magnetic field. The conductive projectile, which is placed between the rails, experiences a Lorentz force and is propelled forward at high speeds.

## 3. What is the force behind a rail gun?

The force behind a rail gun is the Lorentz force, which is the force exerted on a charged particle by an electric and magnetic field. In this case, the electric field is created by the high voltage between the rails and the magnetic field is created by the current flowing through the rails.

## 4. How does friction affect the performance of a rail gun?

Friction can greatly affect the performance of a rail gun by reducing the speed and efficiency of the projectile. Friction between the rails and the projectile can cause heat build-up, which can lead to melting or damage to the rails. It is important to minimize friction in order to achieve maximum velocity and accuracy.

## 5. What are the practical applications of rail guns?

Rail guns have several potential applications, including military use as a long-range weapon, launching spacecrafts, and propelling vehicles. They can also be used in industrial settings for launching payloads or conducting experiments that require high velocities.

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