# Calculating Momentum in a Sword Swing

• fake_it_real
In summary, the conversation revolves around a discussion on a fantasy forum where the main character stops a sword blow with the power of 1 million sword swings. The person discussing the issue finds this idea to be unrealistic and uses physics to show the absurdity of it. However, they are unsure about the exact impact of the strike and the rate of acceleration. Another person adds that the weight of the attacker would be 154,323,584 pounds, which could potentially harm the other person. It is also mentioned that a person's weight does not affect the power of a sword swing.

#### fake_it_real

Hi,

I'm discussing an issue on a forum with someone. I get the feeling that I am trying to be rational with this person while he is NOT being rational with me.

This may sound a bit dumb, but it's kind of like a fantasy forum. In the story in question, the main character stops a sword blow which has been described as having the power of 1 million sword swings.

I thought this sounded really stupid cause I know 1 million is a really big number. I'd like to use a bit of physics so show just how dumb the idea really sounds, but I myself am very stupid.

I calculated that an average person with a weight of 70kg x 1 million would weigh 70,000,000kg. However, a sword swing also has momentum, so the weight of the strike would actually be greater than 70 million kg, right?

This is on the assumption that the sword swinger is putting all of his 70kg of weight behind the swing, which may not be accurate in a real life context, but in the context of the story I think it is accurate. The context of this scenario is that all of that power is accumulated into a single blade which is swung at it's target.

What I'd like to know is that if, at a distance of roughly 5ft between the two characters, the attacker starts his swing with the power of 1 million men weighing 70kg, how much power is he likely to have at the time that he actually hits the other person, according to the laws of momentum?

Sorry, but I don't really know at what rate he accelerates or if that is even an issue in this equation.

Anyway, thanks for any input offered.

Best post of the day.

EDIT: If he weighs 154,323,584 pounds he could just lay on the guy (if he doesn't fall through the Earth's crust). Also, a fat guy swinging a sword is the same as a skinny guy swinging a sword.

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## 1. How do you calculate the momentum of a sword swing?

The momentum of a sword swing can be calculated by multiplying the mass of the sword by its velocity. This can be represented by the equation p = m * v, where p is momentum, m is mass, and v is velocity.

## 2. Does the weight of the sword affect its momentum?

Yes, the weight of the sword does affect its momentum. A heavier sword will have a greater mass, resulting in a higher momentum when swung at the same velocity as a lighter sword.

## 3. Is the momentum of a sword swing constant?

No, the momentum of a sword swing is not constant. It changes throughout the swing as the velocity and direction of the sword changes. However, the total momentum of the sword remains constant unless acted upon by an external force.

## 4. How does the length of the sword affect its momentum?

The length of the sword can affect its momentum in two ways. First, a longer sword will have a greater mass, resulting in a higher momentum when swung at the same velocity as a shorter sword. Second, a longer sword will have a longer lever arm, allowing for more force to be applied and potentially increasing the momentum of the swing.

## 5. What other factors can affect the momentum of a sword swing?

Other factors that can affect the momentum of a sword swing include the angle and technique of the swing, the strength and skill of the person swinging the sword, and any external forces such as wind or resistance from the target being struck.