# MotorBike physics and Life hacks..

#### bike4life

##### Well-Known Member
Here’s a handy list of all the physics for u non types out there. It’s a bunch of life hacks for building crap.

Rule 1: The tensile yield of a bolt is directly proportional to AREA. So even a small change in diameter will make a big change in strength as it’s radius SQUARED. U know not exponential but quadratic which is pretty dam close. Look at the bolt strength charts to tell what to use. And a higher tpi is about 10-20% more strength... “a 1/2” bolt has a tensile of 1,400 and a 1/4” unc has a tensile of about 350. Even a small 1/16” increase to 5/16 makes the strength nearly 2x.

Rule 2: The bending strength of a SOLID SHAPE is directly proportional to height cubed times width. So a 2x6 is 3x as strong as a 2x4 yet not much more money....6^3=216 vs 4^3=64. I know it’s really 3.5 and 5.5 but I rounded... So when building cross members for trailer/shelf go for thin and tall like a skinny person like me. But put some flanges or cross brace if the load is unbalanced and crazy like in a hitch arm where a trailer can tilt and sway... The exception is in torsion and unbalanced load scenarios and in hollow shapes like steel tubing which requires complex math and the rule doesn’t always hold here, but is a good rule of thumb.

Rule 3: Always good PPE and a bucket of water in the shop. I got 3rd burns and lifetime scarring of like 1/2 square foot b/c no bucket of water in the shop...Definetly cut chances of laid due to physical imperfection?? Lucky not on face, but on start on right side of pectorals and stretch down to waist. Hopefully not lim approach 0.But life is life. Comments?

Rule 3: F=ma. And it takes no net force to maintain constant velocity. It does take force mind u, but only EXACTLY enough to the sum of wind drag and tire friction , so when u subtract u get 0 net and in space there is no wind drag which is y ion space ships which are really weak thrust/acceleration than chemical rockets but can travel 10% speed of light like ya know that’s a lot faster than chemical rockets is because it takes no energy to keep this extreme speed of 10million mph, an object in motion maintains constant velocity unless acted on. It only takes energy to accelerate, ion gas crap acceleration but can get high speeds near to speed of light and maintain them at no energy cost just by taking its time. But they cant escape earths atmosphere due to crap acceleration, and force of gravity and air resistance but in space it’s smooth sailing at 1/2 speed of light as it takes no energy to maintain constant velocity unless external force acts on it. Tortoise vs hare?? So it’s easier to stay at 60mph then accelerate at stop lights in the city which is y u get better mpg on freeways then local roads. This is in a perfect world with no friction winds and stuff, too complex to calculate, so take all this with a grain of salt, there are exceptions. Use this knowledge when moped building. If u want like 70mph in a 2 stroke, can be done. Just gonnna take an hour, (exaggerated) to get there.

Rule 4. Momentum=mv. Momentum is conserved. Ok a car traveling at 10mph, 2000lbs has same momentum as u traveling 50mph if u combo weight 400lbs. Luckily at 10mph most of the momentum isn’t transferred to us due to breaking distance and just crap crap efficiency at transferring the momentum to u in collision but at higher speeds it’s much more efficient which is bad for u. This is not good for us as this is y most motorcycle accidents are fatal. It takes an impulse to change momentum, so when u are hit u should roll for a long long time. Acceleration=Changevelocity/time. If hit and u roll, the time will be bigger and acceleration or G force very small.

Rule 5: Stable bikes. Rotational inertia is tendency for object to not fall over ie potholes and stuff. It’s mass times radius squared. In regards to pusher trailers, don’t make them too skinny, add some width. U can also make them heavier but yeah, that adds fuel cost.

Rule 6: making safe turns. Centripetal force is the amount of force the friction between the wheels and road must be so when turning, u don’t flip over. It’s mass x (speed^2) divide by radius. It’s much more efficient to cut your speed down then make larger turn radius as it’s squared, kinda like the bolt example. Highway builders use this to find radius of off ramp by taking the posted speed limit and plug/chug...

I’ll add more as they come to me, right now I am on vacation.

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#### JerboaJohn

##### Well-Known Member
#7 have spares like parts and doodads bcs you lose the tools n misc and maybe the grass isn't mowed n it ate your fasteners...
where's that bolt? it fell right there but... get 6mm allen head cap bolts in 3 lengths. oh and washers. always can use those

#### darwin

##### Well-Known Member
Kid your thinking too much, why create a problem where none exist? Look up the KISS principle and be happy!

#### bike4life

##### Well-Known Member
Kid your thinking too much, why create a problem where none exist? Look up the KISS principle and be happy!
Lol. R u talking about rule 3 or all the other crap. The other crap is useful. I use the bending strength of a beam formula every time I’m building a table or something...

#### JerboaJohn

##### Well-Known Member
yeah but majority of ppl just use the 'know it feel it see it" type of stuff. it's faster and gives ball-park results.
like not the tensile strength data, but knowing a small gauge steel plate equals a really fat aluminum billet. thinking about space but also weight is just something for see and feel even don;t know how many psi it can support.

low tech rules. high tech is hidden in cute packages bcs ppl don;t wanna get bogged down by hairy math tech gizmos n info
K.I.S.S. good rule of thumb but I fight it all the time lol

#### darwin

##### Well-Known Member
Bike4life another thing that will serve you well is learning the different grade of bolts that are out there. Grade 5, grade 8, grade 3 and how to ID them. Metric is the same but with a number system like 8.8 etc.

#### bike4life

##### Well-Known Member
yeah but majority of ppl just use the 'know it feel it see it" type of stuff. it's faster and gives ball-park results.
like not the tensile strength data, but knowing a small gauge steel plate equals a really fat aluminum billet. thinking about space but also weight is just something for see and feel even don;t know how many psi it can support.

low tech rules. high tech is hidden in cute packages bcs ppl don;t wanna get bogged down by hairy math tech gizmos n info
K.I.S.S. good rule of thumb but I fight it all the time lol
never really worked with aluminum billets but plate steel. But with basic formula I do know that I think al has 1/3 the modulus of E of steel. So it would take a plate with around 1.7 times the thickness of steel to get the same bending strength.

#### darwin

##### Well-Known Member
Bike4life, which is stronger? A solid 8" pipe weighing 1lb or an 8" tube weighing 1lb both made of steel?

#### Will'smotobikes19

##### Well-Known Member
Physics are great if you're in school just like the pathagoren theorem but right now I just want something that runs that will ride down the road without weird shimying or problems. Sure if you were designing motorcycles you'd need to know stuff. I want to design my own prototype motorcycle engine small v6 or v8. Ever since I saw the franz flyer I have to build one.

Saw like 4 or 5 bikes past my house this evening rode my piece of crap up the road and the velocity stack choke lever kept flopping down because it's Chinese sheet metal with no locking mechanism!

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#### gary55

##### Well-Known Member
Bike4life, which is stronger? A solid 8" pipe weighing 1lb or an 8" tube weighing 1lb both made of steel?
Wouidn't a pipe and a tube be the same thing, or were you referring to a rod and a tube?

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