Formulae Flashcards
Average Velocity?
Instantaneous velocity?
Average = Δs/t
Instant = gradient of displacement-time graph
Average acceleration?
Instantaneous acceleration?
Average = Δv/t
Instant = gradient of velocity-time graph
Average angular velocity?
Instantaneous angular velocity?
Units?
Average: ω=Δθ/t
Instant = gradient of angle-time graph
Unit = rad s⁻¹
Average angular acceleration?
Instantaneous angular acceleration?
Units?
Average: α=Δω/t
Instantaneous = gradient of tangent to curve of angle-time graph
Units = rad s⁻²
Weight?
Unit?
W=mg
Unit = N (kg m s⁻²)
Coefficient of friction?
Unit?
µ=F/N
No units since it is a ratio
Pressure?
Unit?
p=F/A
Unit = N m⁻²
Unbalanced force?
F=ma
Momentum?
Units?
p=mv
Units = N s
4 equations of linear motion?
v = u+at s = 1/2(u+v)t v² = u²+2as s = ut+1/2at²
4 equations of angular motion?
ω = ω₀+αt θ = 1/2(ω₀+ω)t ω² = ω₀+2αθ θ = ω₀t+1/2αt²
Moment?
Units?
M=Fd
Units = N m
Mechanical advantage?
Units?
MA = dₑ/dᵣ (effort arm/resistance arm)
No units since it is a ratio
Tangential linear velocity?
v=rω
Tangential linear acceleration?
at=rα
Radial linear acceleration?
ar = v²/t = rω²
Angular torque?
M=Iα
Moment of inertia?
Units?
I=mk²
Units = kg m²
General radius of gyration?
k=√(I/m)
Radius of gyration of a solid ring or spoked wheel?
Of a solid disc (e.g. a flywheel)?
k=r
k=1/2r²
Angular momentum?
Units?
L=Iω
Units = kg m² rad s⁻¹
Work?
Units?
w=Fd (force x distance)
Units = J
Power?
Units?
P=w/t
Units = W (J s⁻¹)
Linear kinetic energy?
Units?
KE = 1/2mv²
Units = J
Rotational kinetic energy?
Units?
KE = 1/2Iω²
Units = J
Potential energy?
Units?
PE = mgh
OR
PE = Wh
Units = J
Axial stress?
Units?
σ=F/A
Units = Pa (N m⁻²)
Axial strain?
ε=ΔL/L
Young’s Modulus?
Units?
E=σ/ε
Units = Pa
Rigidity?
Units?
Rigidity = EA
Units = N
Stiffness?
Units?
k = F/ΔL = EA/L
Units = N m⁻¹
Flexibility?
Units?
f = 1/k = ΔL/F = L/EA
Units = m N⁻¹
Strain rate?
Strain rate = Δε/Δt
Coefficient of viscosity?
Units?
η = σ/strain rate
units = Nm⁻² .s (Pa .s)
Shear stress?
Units?
τ = V/A
Units = Pa
Shear strain?
Units?
ϕ = angle sheared = x/d (x = distance sheared; d = distance between 2 shearing forces)
Units = rad
Shear strength?
V required to break/A
Modulus of Rigidity?
Unit?
G = τ/ϕ
Unit = Pa
Variation in stress in layers of a bending beam?
σ = εE = yE/r
Bending moment?
M = Fd (same as normal moment)
Maximum bending moment?
Mmax = σI/ymax
Relationship between variation in stress if a bent beam and maximum bending moment?
M/I = σ/y = E/R
MISYER
Second moment of area of a rectangular bar?
ymax of a rectangular bar?
I = bd³/12
ymax = d/2
Second moment of area of a solid circular bar?
ymax of a solid circular bar?
I = πd⁴/64
ymax = d/2
Second moment of area of a hollow circular bar?
ymax of a hollow circular bar?
I = π(D⁴-d⁴)/64
ymax = D/2
Shear stress in torsion?
Units?
τ = Gθr/L
OR
τ = Gϕ
θ = angle of twist in RADIANS
Shear strain in torsion?
τ = θr/L
Unit = rad
(θ = angle sheared in RADIANS)
Twisting moment?
M = JGθ/L
Relationship between twisting moment, shear strain and shear stress in torsion?
M/J = τ/r = Gθ/L
Polar second moment of area of a solid circular bar?
Units?
J = πd⁴/32
Units = m⁴
Polar second moment of area of a hollow circular bar?
Units?
J = π(D⁴-d⁴)/32
Units = m⁴
Density?
Units?
ρ = mv
Units = kg m⁻³