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Simple machines: The wheel, the screw, and the block-and-tackle
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What is the golden rule of mechanics?
You know what I heard the other day? - Go on, tell me! - Simple Machines! Have you heard about them? - No... - There are several. The wheel, for instance. Yeah, in fact I've heard about the wheel. But is it really a machine?
Yep, a simple turning machine. But they're not turning now. Time for a tire change. Pretty mind blowing that I can lift a two ton car... just using my muscles!
Yep. Thanks to that simple machine. - The jack-screw? - The screw. Is the screw a machine? Yeah, a simple machine. But seriously!
How can I lift the car? I'm not that strong. It's the screw in the jack-screw that gives Mechanical Advantage. When you move the handle, the rotating movement is converted to a movement in the direction of the axis. That's what a screw does.
Does that thing: "What you gain in power you lose in displacement" apply to screws as well? You mean the Golden Rule of Mechanics? Yes, look at the screw in close-up. If that point on the screw rotates once, it moves about six centimetres. At the same time, the screw pushes the nut zero point two-five centimetres in the direction of the screw.
A much smaller displacement, but we have gained in force. What you gain in force, you lose in displacement. But that's a movement in the direction of the screw. The car is moving upwards. Yes, the jackscrew is a nifty combination of several simple machines.
It is a screw -- connected to a clever system of levers that lifts the car. Pretty smart, huh? Yeah. Smart! There.
The spare tire is in place. For how long have these Simple Machines been used? A really long time. You wanna go and have look? Look!
Pulleys and rope. Yes, what do you think that is... ? Ah, gotcha. A simple machine. Of course.
Have you thought about how it works. Something about the golden rule of mechanics, again? You bet! Watch the rope and pulleys. The Stevedore pulls the rope one metre -- But the barrel is only lifted half a metre. "What you gain in power you lose in displacement." You got it.
And when they had to lift really heavy loads, they assembled more pulleys into a "Block and Tackle' to gain Mechanical Advantage. Check it out! Yeah, I get it. Now it gets even easier to lift, but they have to pull even further on the rope. Yes.
The more blocks you add, the more power you win, but you have to pull a longer distance on the rope. Cool! So I can lift an object no matter how heavy, if only I have enough blocks and tackle? No, there is a limit. The more pulleys you use, the more the friction against the rope.
Oh, then it becomes heavy anyway? You got it!From the friction? Okay, what've we got, then? The wheel, the screw, and the pulley block and tackle, we said. Yes, and then there is the inclined plane, the wedge, and the lever.
Simple machines. Okay, let's go -- in my complex machine. Actually, Philip, any complex machine, like your car, is mostly an assembly of simple machines.