Will Thinner Oils Damage Your Engine?
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Kamele0N said:
That reminds me of how we tested compression on our early model Lada cars, during winter, no less. First remove the carb cover and slowly feed a fur hat into the manifold and have someone catch it at the tailpipe. If it came out without any soot, then pistons needed new bore and rings.
In a reciprocating engine, dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft.
Its velocity at either point is zero.
Yes, but velocity = 0 does not mean the body is not in motion. To observe motion (or no motion) you need non-zero dt.
Speed can only be quantified as mentioned by other poster , = dx/dt, yes?
We know the crank is ALWAYS moving as function COS, yes? This proves there is no dt where dx=0, simply not possible.
When speed=0 you made an observation of dt=0, it's a point observation (or some like to say a slice in time), it's not a delta observation.
Speed=0 only says "has no speed at time (t)", it does not say "no motion". The vid uses the words "stops for a brief moment", which is a lie. What's "a brief moment"? To me that says delta-t !=0, which I just proved cannot be, you cannot have a non-zero delta-t where dx=0 for a body in motion, it's not possible, otherwise the connecting rod would at some point rip itself away from the piston.
You realise he's an engineer? he's putting it in layman's terms.
You cannot have the piston change direction by 180 degrees, and not have it "stop" during that process.
The crank is moving rotationally, connecting to something 'hinged' on the piston. It's translating rotational movement to reciprocal movement.
You cannot have the piston change direction by 180 degrees, and not have it "stop" during that process.
The crank is moving rotationally, connecting to something 'hinged' on the piston. It's translating rotational movement to reciprocal movement.
Who's the engineer?
I then challenge you, if the piston stops moving at TDC and BDC, then you show me when the crank also stops moving.
Fact: it does not "stop", it's speed becomes zero for zero time (dt=0 & dx=0). Speed = 0 for only a point in time.
And, the technical translation is rotational (COS function) to linear motion.
I think folks are referring to the angular dwell time where the piston is in vicinity of a some arbitrary dx for some arbitrary time dt, which is related to the freq of COS function (aka rpm's).
Remember, if you say "for a brief nano-sec", those words mean dt > 0
It never stops moving, not even for a brief 1/1000^100000 sec.
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So, you're saying that you cannot be at zero, to change direction?
You must know of the maths/physics example/joke of the fly hitting the freight train head on?
You need to learn some things. It's not just pistons, it's a lot of other things as well.
Show me. I am open to learning.
How in the world can something change direction 180° but not stop at one point. Makes no sense. The crankshaft is always moving yes but it is not changing direction and is connected to the piston with two separate pivot points.
zero is the speed, the scalar of the velocity vector.
again, there is no dt > 0 where dx = 0
What that means is, it's NOT stopped. Just because you make observation at some time (t) where you observe speed = 0, that observation alone does not mean there is no motion.
Stopped means stopped, that's when for any dt > 0 you have a dx=0. The body has zero x1-x0 for that dt = no motion = stopped.
Again, if the piston stopped for any period of time (when running) the engine would go pooof.
Like the speed of a tire at the contact point.
You can move your vehicle from forward to reverse motion as quickly as you want but at some point your tires are going to stop rotating
Define "stopped" mathematically, then I can continue to explain.
The crank is ALWAYS changing direction, if it wasn't then the piston would not go up and down.
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Then how does the piston reach a maximum velocity?
The connecting rod journal, maybe. Even then it is always rotating the same direction. I mean the earth moves three different ways all at the same time.
The crankshaft centerline is always rotating the same direction.
It reaches max speed (a scalar component of the velocity vector) in one direction when the crank arm is exactly 90deg from line of linear motion.
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