When you shoot a bullet on ice or into ice, the bullet might continue to spin.
Why do bullets spin on ice?
Bullets spin on ice because of how bullets and guns operate. Bullets pass through spiraled grooves in a gun barrel. The grooves make the bullet spin. When a bullet hits ice, the force of impact can stop the forward movement of the bullet before it stops the rotational movement of the bullet.
In this article, we’ll cover everything you need to know about why bullets spin on ice.
Why Do Bullets Spin on Ice? (Detailed Explanation)
Bullets spin on ice because of how guns are made, how bullets stabilize in flight, physics, and the properties of ice.
Let’s break down each part of the explanation in more detail.
Bullets Spin on Ice Because of the Rifling of Gun Barrels
Most people have seen a spinning bullet in a movie or TV show, and while it looks impressive, it’s actually based on real physics.
Bullets spin because of the rifling in gun barrels.
Rifling is a series of spiral grooves that are cut into the barrel of a gun. When the bullet is fired, the rotational force of the expanding gases causes it to spin.
Bullets Spin To Stay Airborne and Stabilized
The rotation stabilizes the bullet while it is airborne, keeping it on a more accurate and direct path toward a target.
It also makes the bullet less likely to be affected by crosswinds. The physics of rifling is complex, but suffice it to say that it’s an essential part of modern firearms design. Without it, bullets would be much less accurate and would be more likely to veer off target.
If you were to shoot a bullet without any spin, it would likely tumble end over end and would not be very accurate.
When you see a bullet spinning on ice, know that it’s spinning for a good reason.
The Properties of Ice
Bullets spin on ice because of the properties of ice.
The main property of ice that causes this is its high density. When a bullet hits the surface of the ice, it pushes against the ice molecules, causing them to move out of the way.
The high density of the ice means that there are more molecules per square inch than in air, so the bullet has to push harder to move them. This resistance to movement stops the bullet but does not always stop the bullet from spinning or rotating.
Another property of ice that contributes to this effect is its low friction.
Friction is a natural force that resists motion, and it is created when two surfaces rub together.
The lower the friction between two separate surfaces (i.e. bullets and ice), the easier it is for one object to slide over another. Ice possesses an extremely low friction coefficient.
To say that differently, ice is slippery.
Ice provides a smooth surface for the bullet to rotate on. The smooth surface of the ice helps to reduce friction between the bullet and the ice. This, in turn, minimizes the volume of energy needed to spin the bullet.
As a result, bullets can spin on ice without using much energy.
Why Do Bullets Spin on Ice? (Mythbusters)
The famous guys behind the Mythbusters television show did an entire episode about “Why Do Bullets Spin on Ice.”
The exact episode is episode 7 of season 9.
In the episode, the cast rigged a handgun to fire directly into the ice and snow at a 42-degree angle Using a rope to pull back the trigger, they fired the shot.
Then the cast rushed over to find the bullet and examine their results.
They found the bullet lodged into the ice but it wasn’t spinning.
So, they repeated the test over and over again with the same non-spinning results. They even filmed the bullet exploding out of the barrel in slow motion.
Here is the video so that you can see the experiment in action (Note: Keep the volume low. The end of the video gets very loud):
But the Mythbusters crew didn’t give up.
They thought that perhaps the bullets were not rotating because they were hitting the ice and ricocheting into the snow. Therefore, they repositioned their “robot-gun” to fire more centrally into the thick ice.
Then, they stood back and pulled the string.
When the gun went off, the cast once again rushed over to see the results. This time, they watched in awe as the bullet stuck in the ice kept spinning.
You really must see the video of the spinning bullet to know how cool it looks.
Do All Bullets Spin on Ice?
Not all bullets will spin on ice. Only “full metal jacket” bullets spin. Hollow-point slugs or soft-point slugs do not spin. Instead, they flatten out on the ice.
Full metal jacket bullets are made with a soft core of lead that is surrounded by a harder shell of metal.
The metal shell helps to keep the bullet from deforming when it hits a hard surface like ice. The soft lead core helps to increase the weight of the bullet and also makes it easier for the bullet to spin.
Hollow-point slugs and soft-point slugs don’t spin on ice because they are made with a soft lead core that is surrounded by a thin metal jacket. The thin metal jacket does not provide enough support to prevent the bullet from deforming when it hits a hard surface.
As a result, these types of bullets will flatten out on the ice instead of spinning.
Do Bullets Have To Bounce on the Ice to Spin?
Bullets that spin on ice first bounce or ricochet off of the ice.
The bouncing action slows the forward momentum without slowing the rotational momentum of the bullet.
The spinning ice bullet is following a concept called the conservation of angular momentum. This is a law of physics that states that the angular momentum of an object will remain constant unless acted upon by an outside force.
The forward momentum of the bullet is decreased when it collides with the ice. However, the rotational momentum remains the same.
As a result, the bullet will start to spin on the ice.
When Do Bullets Not Spin On Ice?
There are several reasons a bullet will not spin on ice.
Some of these reasons include:
- The bullet is not a full metal jacket
- The bullet is fired directly into the ice (instead of bouncing)
- The bullet does not experience precession or gyroscopic effects
- The surface of the ice is too rough
- The bullet is not fired at a high enough velocity to overcome friction
Final Thoughts: Why Do Bullets Spin on Ice?
I remember the first time I witnessed a bullet spinning on the ice in person.
It was like watching an illusionist perform a magic trick. The spinning bullet seemed to defy the laws of physics.
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Sources
Frontiers in Physics (Research Journal)
ScienceABC (How Rifling Works)