Railgun and the laws of physics

In summary, the conversation discusses the creation of a rail gun using two ring stand poles, a steel ball, and a car battery. Despite being level, the rail gun shoots the ball in the wrong direction, defying the laws of physics and the right hand rule. The group hypothesizes that the cause could be an odd number of sign errors or the resultant of the electromagnetic force acting below the line of contact between the ball and the supporting edges. To test this theory, they placed a bowling ball on two tables and observed that a force applied horizontally on the bottom of the ball caused it to roll away from them. They also speculate that the majority of the current is conducting over the bottom surface of the ball, causing the Lorentz
  • #1
Cbixel
4
0
I just made a rail gun using two ring stand poles, a steel ball, and a car battery. Maximum velocity is about 5 cm/sec.

What is strange is that it is shooting the wrong way. Defying the laws of physics and right hand rule. Any ideas ?
 
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  • #2
How do we know that is "defying" the laws?
You don't bother to give any details.
 
  • #3
Cbixel said:
What is strange is that it is shooting the wrong way. Defying the laws of physics and right hand rule. Any ideas ?

Usually this happens because you've made an odd number of sign errors. Professional scientists and engineers have gone through years of formal training to ensure that they know to always make an even number of sign errors. (Note that making zero errors is a special case of making an even number of errors, and is generally considered to represent an unrealistic and unnecessary ideal).

OK, kidding, aside... You'll have to tell us a lot more about your setup before we'll be able to tell you why your getting the result you're observing.
 
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Likes cosmik debris and Bystander
  • #4
5cm/sec ?
 
  • #5
I would definitely like to see that setup. The only thing I can imagine is that you put the ring poles in parallel to create the rail. But what creates the force on the ball?

Also, yeah, 5cm/s? That's 0.18km/h. Are you sure your rail isn't just not completely level and the ball just rolls due to gravity?
 
  • #6
So, its pretty level. The ball will not roll without a current applied. If I give it a push either direction, it rolls about the same distance before stopping, so its reasonably level.

So, the right hand rule says the force should be away from me. I am at the end of the two rails that is attached to the battery, so:
  • The current goes out the right rail (mag field up between rails).
  • The current comes back on the left rail. (mag field up between rails)
  • Current through steel ball is from right rail to left rail.
  • Right Hand Rule (Current from right to left through ball, plus mag field up = force away from me)
Switching the direction of current in the whole system should not have any effect, as both mag field and current through ball change directions, so force should still be away from me.

Perhaps I have created a left handed rail gun...

Anyway, if I put a small wire across the two rails, the wire moves away from me as would be expected. I am looking at torques on the the ball...
 
  • #7
What is limiting the current from the car battery? You're not shorting it out, are you? That can be pretty dangerous...
 
  • #8
I think that a force acting away from you can result in the ball rolling towards you.
 
  • #9
The cause for that above behavior is very different though. If the spool didn't have that footstand to keep it a centimeter off the paper, the effect wouldn't happen.
 
  • #10
I am not saying that this is the case here. I have no idea of the geometry or about where the electromagnetic force acts, relative to the supporting surfaces.
Just a possibility.
I was thinking about a situation with the resultant of the electromagnetic force acting somewhere below the line of contact between the ball and the supporting edges. If there are any edges.
 
  • #11
I think I have it figured out. The force is, in fact, in the expected direction, or away from me. But, because the ball is between two rails, the axis of rotation is at the elevation of the points of contact between the ball and the rails. Thus, the force, away from me, is acting below the axis of rotation and creating a torque that spins the bottom of the ball away from me and the ball rolls toward me. This is different than the string on the spool demonstration, where the force is above the axis of rotation.

To test this theory out, we placed two tables 6 inches apart, and placed a bowling ball in the gap. A piece of tape attached onto the bottom of the ball and pulled toward us horizontally did, in fact, roll the ball away from us.
 
  • #12
Also, we think the majority of the current must be conducting over the bottom surface of the ball, and thus, this is where the Lorentz force is acting.

I am just glad I did not accidentally create the first "left handed railgun" ever.
 
  • #13
Mightn't you be dealing with the Faraday cage effect since you are using a metal ball?
 

Related to Railgun and the laws of physics

1. What is a railgun and how does it work?

A railgun is a type of electromagnetic weapon that uses electric and magnetic forces to accelerate a projectile to high speeds. It consists of two parallel conductive rails, with a sliding armature or projectile between them. When a high voltage is applied to the rails, it creates a powerful magnetic field, which accelerates the projectile along the rails and out of the gun. The projectile can reach speeds of up to Mach 7, making it a highly effective weapon.

2. What are the laws of physics that govern the operation of a railgun?

The laws of physics that govern the operation of a railgun are primarily related to electricity and magnetism. These include Ampere's law, which describes the relationship between electric current and magnetic fields, and Faraday's law of induction, which explains how changing magnetic fields can induce electric currents. The conservation of energy and momentum also play a role in determining the speed and trajectory of the projectile.

3. What types of materials are used in a railgun?

A railgun requires materials that can conduct electricity and withstand high temperatures and pressures. The most commonly used materials are copper for the rails and a non-conductive material, such as plastic or ceramic, for the insulating layer between the rails. The projectile is typically made of a conductive material, such as aluminum or a combination of metals, to allow for the flow of current.

4. What are the advantages of using a railgun compared to traditional guns?

One of the main advantages of a railgun is its incredible speed and range. The projectile can travel at hypersonic speeds, making it nearly impossible for traditional guns to match its velocity. Railguns also have a longer effective range and are more accurate, as they are not affected by factors such as air resistance and gravity. Additionally, railguns do not require explosive propellants, making them safer and more environmentally friendly.

5. Are there any limitations to the use of railguns?

While railguns have many advantages, they also have some limitations. One of the main challenges is the large amount of energy required to power a railgun, which can be a logistical and operational hurdle. Additionally, the high velocities and forces involved can cause wear and tear on the rails and other components, leading to maintenance and durability issues. However, with ongoing advancements in technology, these limitations are being addressed and railgun technology continues to improve.

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