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Listen to a lecture in a physics class.
Now answer the questions using your notes.
Type your notes here:
Now answer the questions using your notes.
Type your notes here:
Summarize the text using your notes.
Type your notes here:
Listen again
M: Let's move on to simple machines. You probably remember that in physics, a simple machine is any mechanism or device that requires force from only one source in order to work. In class, we only had a chance to get sort of a broad overview of these machines. But today, I want to go into more detail about the types of simple machines there are and the kind of work they perform. Why don't we start with the pulley? In a nutshell, a pulley is kind of like a wheel that has a groove in it. Then there's a rope that runs through the grove in the wheel. The pulley is used to change the direction of the force that is applied to the rope. So, in the most basic pulley systems, you pull the rope to help lift something that is attached to the other end of the rope. I'm sure you've all seen pulleys at work before. Now, there are three types of pulley systems that I'd like to discuss. The first type is called a fixed-base pulley. For this type, the axle of the wheel is secured in one place. And when you pull on the rope, you basically just change the direction of the force currently on the rope. Does that make sense to you? So when you pull on the rope it makes it easier to lift whatever is attached to the other end of the rope. Let me give you an example. OK, urn, right. Picture this. Imagine a fixed base pulley as the type used on flag poles to help people raise flags.
W: It doesn't seem like that kind of pulley would really be useful for anything but raising something light... like a flag. There's a kind of pulley that can lift heavier things, right?
M: That's right. It's called a movable base pulley. You probably guessed that the main characteristic for this type of pulley is that the pulley—the wheel's axis moves. This is pretty helpful, especially if you want to multiply the force being exerted on the rope. When you multiply the forces on the rope, you're increasing the mechanical advantage of this simple machine. This means that when you pull on the rope, you will have double the force on the object attached on the other end. OK, let's move on to the last type of pulley: the compound pulley. A compound pulley mixes both fixed base and movable base pulleys.
Compound pulleys are a good way to give yourself an even better mechanical advantage over the' pulleys involved in your simple machine. In theory, the more pulleys you add, the more mechanical advantage you create, but in reality, every additional pulley adds more friction. And if you have too much friction as a result of too many pulleys, you eliminate any advantage that you might have gained.
