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Lines changed: 15 additions & 122 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,10 @@
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Improvmenet:
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notation
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formulas
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tests
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Box on an incline
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=================
@@ -10,6 +17,7 @@ All vectors are in newton.
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Notation:
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fg = gravitational accelleration
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m = mass of box
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> fg = V2 0 (-10)
@@ -28,61 +36,24 @@ The normal against the incline:
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> fn :: Vector2 Double -> Angle -> Vector2 Double
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> fn fa a = negate (f_l_ fa a)
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Frictionfree incline:
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Friction free incline:
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Force resultant:
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Resulting force:
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> fr :: Vector2 Double -> Angle -> Vector2 Double
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> fr fa a = (fn fa a) + fa
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With friction:
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** Tests:**
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------------
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*Main> fr (V2 0 10) 0
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(0.0 x, 0.0 y)
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Good: No inclination - stands still.
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*Main> fr (V2 0 (-10)) 0
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(0.0 x, -20.0 y)
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Odd: Motsatt gravitation ger något underligt? Vi säger fortfarande att normalen är magnituden
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*Main> fr (V2 0 10) (pi/2)
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(-6.123233995736766e-16 x, 10.0 y)
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Good: 90* lutning - faller med G.
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*Main> fr (V2 0 10) (pi/3)
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(-4.330127018922194 x, 7.499999999999999 y)
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*Main> fr (V2 0 10) (pi/4)
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(-5.0 x, 4.999999999999999 y)
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*Main> fr (V2 0 10) (pi/6)
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(-4.330127018922193 x, 2.499999999999999 y)
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**Frictionconstant - in motion:**
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\begin{align}
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F_{friction} = \mu * F_{normal} \iff \mu = \frac{F_{friction}}{F_{normal}}
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\end{align}
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$$ F_{friction} = \mu * F_{normal} \iff \mu = \frac{F_{friction}}{F_{normal}} $$
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> us = 0.5
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> uk = 0.4
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Add image how friction depends if there is movement.
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![Friction](friction.png){.float-img-left}
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> type FricConst = Double
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Friction:
@@ -94,7 +65,7 @@ Friction:
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We have the normal force and only needs the constants.
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The current speed does not affect the friction. However F*M = Nm = work = J -> racer cars burn tires.
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The current speed does not affect the friction.
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> motscalar :: FricConst -> Vector2 Double -> Scalar
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> motscalar u f = u * (magnitude f)
@@ -122,81 +93,3 @@ Now we just need to sum the force vectors:
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> fru' fa a u = (motkraftv u (fn fa a) (fr fa a))
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Hmm om jag försöker skala riktningsvektorer till sin enhetsvektor så blir det blub med nollvektorn.
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enh_vekt v = scale (1 / (magnitude v)) v
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$ enh_vekt (V2 0 0)
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(NaN x, NaN y)
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Jag skulle anta att enh_vekt bara gäller då (magnitude v) =/= 0.
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Fixed nollvektorn.
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*Main> fru fg (pi/4) 0
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(-5.0 x, 4.999999999999999 y)
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*Main> fru fg (pi/4) 1
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(1.7763568394002505e-15 x, -1.7763568394002505e-15 y)
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*Main> fru fg (pi/4) 0.5
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(-2.499999999999999 x, 2.4999999999999987 y)
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Ugh? Den är linjär? 1 i friktionskoeff = full stop. alltid?
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När är isf motkraften = fallkraften?
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*Main> fru fg 0 5
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(0.0 x, 0.0 y)
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*Main> fru fg 0 1
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(0.0 x, 0.0 y)
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*Main> fru fg (pi/2) 10
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(-6.123233995736762e-16 x, 9.999999999999995 y)
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Hmm?
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*Main> fru fg (pi/6) 1
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(3.169872981077808 x, -1.8301270189221936 y)
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*Main> fru fg (pi/6) 0
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(-4.330127018922193 x, 2.499999999999999 y)
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*Main> fru fg (pi/6) 100000
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(749995.6698729811 x, -433010.2018922193 y)
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Den statiska friktionen är konstig. Den borde stå still vid låg vinkel o hög friktion.
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Jag summerar ju visserligen krafterna, så det är nog något lurt med friktionshanteringen.
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Tests:
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fr
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*Main> fr fg (pi/3)
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(-4.330127018922194 x, 7.499999999999999 y)
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*Main> fr fg (pi/6)
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(-4.330127018922193 x, 2.499999999999999 y)
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fru
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*Main> fru fg (pi/3) 1
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(-1.8301270189221928 x, 3.1698729810778055 y)
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*Main> fru fg (pi/6) 1
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(3.169872981077808 x, -1.8301270189221936 y)
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fru'
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*Main> fru' fg (pi/3) 1
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(2.500000000000001 x, -4.330127018922194 y)
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*Main> fru' fg (pi/6) 1
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(7.500000000000001 x, -4.330127018922193 y
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wtf händer? Hur kan fr ha samma x-vektor för två olika vinklar inom samma kvadrant?
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fn
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*Main> fn fg (pi/3)
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(-4.330127018922194 x, -2.500000000000001 y)
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*Main> fn fg (pi/6)
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(-4.330127018922193 x, -7.500000000000001 y)
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