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- We've talked about engines before,
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and I don't know if I'll ever get tired of it.
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The air gets compressed by the piston,
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and the spark...
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What?
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No, stop it!
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There's no piston here!
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What if I told you we could skip all of that crap?
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Not worry about turning downward force into rotational force
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and cut the size of the gall dang engine in half?
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That's the Wankel rotary engine!
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In 1951, Felix Wankel got this idea in his head
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that if you put a triangular rotor in a well-designed
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circely, oval-ish shape, you could make an engine
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that took care of intake, compression, combustion,
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and exhaust, just like the traditional piston-drive
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Otto Cylce engine.
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And because it's a spinning motion, you wouldn't need
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to worry about crankshafts and valves and timing belts
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and lifters and all that crap that other people
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are goofin' around with.
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He had some trouble getting it right, though.
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So it was in 1961 that Mazda, intrigued by this idea,
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helped him out, and here's how it works.
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A curved triangle sits in the engine.
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It's what'll drive the driveshaft, which is also weird.
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Instead of a piston, this magic triangle is called a rotor,
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because it spins.
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The rotor sits inside of a housing and rotates
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around a fixed gear attached to the housing.
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This gear makes sure that the rotor follows the right path,
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so it's not just floating around in there.
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The rotor then spins an eccentric output shaft,
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and this is what'll give the car moving.
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You can call it a driveshaft if you want,
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I'll know what you're talking about.
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But just the names of the parts should let you know
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that the Wankel rotary engine plays by its own rules.
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Now that we know the parts, let's see how they fit together
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and make the boom.
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We'll start with the intake.
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As the triangle-shaped rotor draws away from the wall
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of the housing, it's creating a vacuum.
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As it passes the intake hole, it continues to pull away
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from the wall, drawing the air-fuel mixture
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into the chamber it's creating, just like a piston
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would draw air in on its intake stroke.
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When the peak of the rotor passes the intake port,
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well, now that chamber's sealed.
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The rotation of the triangle, still sealed against
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the housing, begins to compress the air-fuel mixture
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as it continues its rotation.
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When the air is as compressed as it can be and the rotor
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has just a bit more mass on the other side of the chamber,
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a spark triggers the combustion.
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The combustion chamber is long.
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If there's only one plug, the flame would spread too slowly
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to be effective at producing power.
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Most rotary engines have two sparkplugs.
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When the sparkplugs ignite the air-fuel mixture, kapow!
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It forces the rotor to move in a direction
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that allows the combustion reaction to expand,
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continuing the rotor's journey around the housing.
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The combustion gasses continue to expand, moving the rotors
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and creating power, until the peak of the rotor
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passes the exhaust port.
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Just like the rotor compressed the air-fuel mixture
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against the wall with the sparkplugs, on this side
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of the housing, the rotor pushes the exhaust gasses
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out of the exhaust port.
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And if you look at the other point of the triangle,
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the rotor is beginning to draw air into the intake chamber
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just as it's finishing with the exhaust down here!
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So the cycle continues, over and over and over
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and over and over and over, and it continues to go
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over and over and over.
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But unlike the jerky up-and-down motion of the pistons,
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the rotor moves, just like my favorite band,
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in one direction.
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♪ You don't know you're beautiful ♪
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There's so much rubbing going on between the rotor
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and the housing that that gave Wankel a lot of problems
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as he was designing.
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Engineers realized that a hole to let in the engine oil
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would reduce wear on the rotor and housing.
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Also, to make sure that no chamber of the combustion cycle
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loses pressure, apex seals cap the point of the triangle.
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These tweaks are what took Wankel's early underwhelming
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experiments from curiosity to practicality.
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And look at this triangle!
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With three sides, as soon as one side begins,
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let's say, combustion, another side is completing
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exhaust while the third side is drawing in air and gas!
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So, unlike a traditional piston-driven engine,
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which would need three cylinders to do that,
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like the rare but very real in-line three, you only need
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one active component, the rotor, to have three stages
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of engine combustion occurring simultaniously.
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The way Mazda did it on their engines,
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like what powered the RX7 and RX8,
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was to put two rotors that complimented each-other,
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so when one rotor was entering combustion,
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the other was about to enter combustion.
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You can see how evenly a Wankel rotary engine
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can deliver power versus the herky-jerky up and down
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of a piston-driven engine.
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This evenly-driven rotational force spinning the rotors
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drives the output shaft.
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The output shaft has round lobes mounted eccentrically,
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meaning they're offset from the center line of the shaft.
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Each rotor fits over one of these lobes.
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The lobes act sort of like the crankshaft
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in a piston engine.
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As the rotor follows its path around the housing,
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it pushes on the lobes.
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Since the lobes are mounted eccentric to the output shaft,
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the force that the rotor applies to the lobes
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creates torque in the shaft and makes it spin.
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This makes the eccentric shaft move three turns
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for each turn of the rotor, and that's why these engines
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can create such high rev.
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(engine revving)
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And if you check out the horsepower versus torque video,
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you'll know horsepower is how quickly
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force can be produced.
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A high-revving engine doesn't need as much torque
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to generate more horsepower,
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because it's delivering it so quickly.
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And, like Mazda did with the RX7, they can be turboed,
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just like any other engine.
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And again, because they're revving so high, a turboed Wankel
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doesn't have to worry half as much about lag!
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Some lag!
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So, what are some other benefits of a rotary engine?
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First, there's fewer moving parts.
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No lifters, no push rods, no camshafts.
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All those little things that can go wrong in
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a traditional engine simply aren't there in a Wankel,
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so they can't break.
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In a two-rotor Wankel, you got two rotors and one e-shaft
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to worry about, that's it.
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And that means these engines can rev higher
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and not bust any of those intricate parts.
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And also?
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You don't need four, five, six cylinders,
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you've got an engine delivering consistent power,
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making awesome noises!
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(engine revving)
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And taking up half the room of other engines!
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Oh!
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And sometimes, when it gets moving really quick,
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you get this!
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(backfiring)
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That is pretty cool!
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But that's also a drawback.
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Wankels use a lot of gas because they have
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a low compression ratio.
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When they get moving like that, they make those
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sweet-ass flames 'cause they're shooting out exhaust gasses
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with unburnt hydrocarbons.
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That's not good for fuel economy,
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and it's not good for the air!
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Also, remember how they're lubed with oil
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throughout the housing?
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That oil burns when it's hot.
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That means more burnt less clean hydrocarbons,
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which is tough for emissions.
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You remember how they sealed up the different chambers
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created by the rotor.
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Remember, from before?
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Uh, yeah.
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You can blow an apex seal, and if that happens...
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(screaming)
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Those chambers bleed into one another
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and you lose most of the benefits that made you fall in love
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with your screaming rotary engine in the first place.
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Between being different and being good,
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Wankel rotaries are pretty rad.
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Wankel rotary engines!
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If you like the way we show how things work
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on Science Garage, then you really need to check out
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Brilliant.org.
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Brilliant is math and science enrichment learning.
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It's engaging, and instead of just getting talked at
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about how thing worked, Brilliant is set up
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to let you really get in there and apply
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what you're learning.
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The sequences lead you to thought-provoking,
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challenging problems, and that helps you understand
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concepts at a deeper level.
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Actively solving problems becomes an addictive,
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interactive experience, and I gotta tell you,
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it's pretty cool.
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How do you think the brain trust we just talked about
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created the Wankel rotary engine?
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They had a deep understanding of physics
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and practical application and problem-solving,
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just like the courses at Brilliant.org.
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A great place to start is with Physics of the Everyday.
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This course gets into how things work, things you use
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every day, just like we do here on Science Garage!
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To learn more about Brilliant,
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go to Brilliant.org/sciencegarage and sign up for free!
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Also, the first 200 people to go to the link
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will get 20% off their annual premium subscription!
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I'll see you there!
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Brilliant!
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And follow me on Instagram, @bidsbarto,
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and follow Donut, @donutmedia.
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We got shirts like this, and we got new designs comin' soon.
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Guys, we do this every Wednesday!
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Make sure you subscribe, hit the yellow button
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so you get notifications!
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Like the RX7, you can learn about turbochargers here,
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and you can learn about the RX7 in this episode
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of Up to Speed!
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Don't tell my wife these engines can be a hassle,
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'cause I'm trying to get one.