Everyone has the same comment about Batman: He’s cool because he’s just a normal dude, but he’s also a superhero. It’s true, he doesn’t have superpowers. However, what he does have is a combination of skills and equipment.
In the movie The Batmanwe get to see him use one of his “toys”—his ascender gun. (It’s also known as a grapple gun or a grappling gun.) Batman uses it to launch something like a grappling hook, which is connected to a cable. Once it attaches to a high point, an electric motor within the gun winds the cable, pulling Batman up.
In this sceneBatman is in a building with a bunch of Gotham police officers who have detained him. He doesn’t think that’s such a good idea. After breaking free, he runs to an interior stairwell and shoots the ascender cable up near the stairwell’s top, then activates the motor to pull him up. Spoiler: He escapes. (But you probably knew that.)
Now for the physics calculations: What kind of battery or power source would his ascender need, and how much power would it use? Let’s start with a bit of background on energy.
Energy for the Ascent
One of the key ideas for understanding energy is to define a system of interest, which is the collection of objects we want to study. (Of course, the most complete system is the entire universe, but it’s not very practical to deal with the whole universe thing all at once. Instead, we want to isolate only the objects that we are interested in.)
Let’s use the following system: Batman plus the ascender (and its battery) and the Earth. (You might think the Earth is a weird thing to add to the system, but just hold on. We’ll get there.)
Once we have a system, we can use one of the most important concepts in physics: the work-energy principle. This says that the work done on a system is equal to the change in the system’s energy. But what the heck is energy?
That’s actually a hard question, but here is my best answer: Energy is not a real thing, but rather a way to keep track of different interactions. Energy also comes in different forms. For example, kinetic energy is associated with the motion of objects , and potential energy is the kind that depends on the position of objects.
So work is a way to add or take away energy from a system. In terms of forces, we define work as the following: