I am super pumped up about the Iron Fist series that will premiere on Netflix soon. At this point, all I really have is this trailer---but that has never stopped me before. Why would it stop me now?
If you don't know anything about Iron Fist, let me say one important thing. Other than being a martial arts guy, he also has the ability to make this superpowered punch. (That's what's going on in the trailer when his hand gets all glowing and stuff.) But how much energy is in his power punch? To answer this question, I'll analyze the scene right at the end of the trailer, where Iron Fist punches the floor and sends at least two humans flying into the air.
Here's the important part for our analysis:
I'm going to make the following estimations and assumptions.
- There are two humans (other than Danny Rand) that get tossed into the air. There is also some other stuff---like chairs and things you would find in the room. I am going to estimate the total mass of thrown stuff at 200 kg.
- It's difficult to see, but it almost looks like the humans get thrown up to the ceiling of the room. I am going to use a maximum height of 2 meters. If you don't like this value, you can create your own estimation.
- All of the energy needed to raise the bad guys (assuming they are bad) comes from Iron Fist's iron fist punch.
I can find the energy in the punch by using the work-energy principle. This says that if there are no external inputs into a system, the change in energy is zero. For this case, I will use a system consisting of Iron Fist, the baddies, the other debris, and the Earth.
Next I need to pick a starting and ending time to compare energies. I will draw this as a diagram.
In this system, I essentially have just two types of energy to deal with. First, there is the stored energy in the iron fist (the punch, not the person). I guess this would be some type of potential energy, but I'm not exactly sure how the punch works. Second, there is a change in gravitational potential energy. If the starting center of mass of the humans is set at zero potential energy, then the height they rise will give me the total change in gravitational potential energy.
I can write this energy conservation as:
It's really that simple. The energy from the punch goes into the change in potential energy for all the stuff moving up. All I need to do now is put in my values for the mass of the stuff and the height. This gives an estimated energy in the punch with a value of 3,920 Joules. That might seem like a lot, but you probably have 30,000 Joules stored in your smartphone battery. A ham and cheese sandwich has about 1.5 million Joules.
It's not enough energy for a phone, but 3,920 Joules is a large value for a human punch. What about the power? The power is defined as the rate of energy change.
For the iron fist punch, I know the energy already. But what about the time? I can look at the time it takes the Iron Fist to perform this super punch and then calculate the power. Using Tracker Video Analysis (just to get the time), I get a punch time of 0.417 seconds. I'm assuming he builds up all the energy during the swinging motion (but of course that is pure speculation). This would give a power of 9,400 Watts. That is some serious power. Just for comparison, an MMA fighter might have a punch energy of 25 Joules with a power of about 50 Watts.
I can't leave you without homework questions. Here you go.
- Suppose all the energy in Iron Fist's punch is a type of kinetic energy. What would the mass of Iron Fist's hand have to be to produce a kinetic energy of 3,920 Joules? You will have to estimate the speed of his fist.
- Instead of estimating the speed of a fist in a punch, you can do something different. If you assume a constant acceleration during the punch, you can get a final fist velocity based on the distance the fist moves and the time of the swing (which I already gave you).
- How does this iron fist punch even work? Where does the energy come from? Find some creative way to explain this punch. (This is good practice for when you will eventually become a science consultant for superhero movies.)
- Look at the rest of the trailer. Are there any other scenes that you could use to estimate the power of the iron fist punch?
- Let's go with the idea that Iron Fist's fist increases in mass during the punch. Find the momentum of the iron fist punch. Estimate how far back a human would fly after being hit by this punch.
