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Math was never the problem. The explanation was.

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Can you reverse the spin of this tetrahedron?

Can you reverse the spin of this tetrahedron?

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Can you reverse the spin of these snakes?

Can you reverse the spin of these snakes?

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A turnstile antenna is two crossed dipoles driven 90° apart, one dipole p turning at ω about its mast. Its far field E ∝ r̂ × (r̂ × p̈(t − r/c)) has phase ωt − kr − φ at every latitude, so each wavefront is the spiral r = (ωt − φ − 2πn)/k. Along the mast E ∝ (1/r)[cos(kr − ωt) ŷ + sin(kr − ωt) x̂] keeps its length and turns once per period, and B = (1/c) r̂ × E turns with it. In the plane of the cross the same wave is linearly polarized.

A turnstile antenna is two crossed dipoles driven 90° apart, one dipole p turning at ω about its mast. Its far field E ∝ r̂ × (r̂ × p̈(t − r/c)) has phase ωt − kr − φ at every latitude, so each wavefront is the spiral r = (ωt − φ − 2πn)/k. Along the mast E ∝ (1/r)[cos(kr − ωt) ŷ + sin(kr − ωt) x̂] keeps its length and turns once per period, and B = (1/c) r̂ × E turns with it. In the plane of the cross the same wave is linearly polarized.

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Can you reverse the spin of this ambiguous sphere with your mind?

Can you reverse the spin of this ambiguous sphere with your mind?

265,958 просмотров

Can you reverse the spin of this trefoil knot?

Can you reverse the spin of this trefoil knot?

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An electric dipole p(t) = p₀ sin(ωt) ẑ oscillating at a point radiates a field that, far away, falls off only as 1/r. Its radiation term is E = (μ₀/4π) p̈(t − r/c) sin θ / r along θ̂, with B = r̂ × E / c along φ̂, so E, B and the direction of travel r̂ are mutually perpendicular. The intensity goes as sin²θ / r²: zero along the axis, strongest at the equator. Every sphere around the source carries the same mean power, p₀²ω⁴ / (12πε₀c³).

An electric dipole p(t) = p₀ sin(ωt) ẑ oscillating at a point radiates a field that, far away, falls off only as 1/r. Its radiation term is E = (μ₀/4π) p̈(t − r/c) sin θ / r along θ̂, with B = r̂ × E / c along φ̂, so E, B and the direction of travel r̂ are mutually perpendicular. The intensity goes as sin²θ / r²: zero along the axis, strongest at the equator. Every sphere around the source carries the same mean power, p₀²ω⁴ / (12πε₀c³).

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Can you reverse the spin of this hyperbolic paraboloid?

Can you reverse the spin of this hyperbolic paraboloid?

89,098 просмотров

Can you reverse the spin of this hourglass?

Can you reverse the spin of this hourglass?

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A Gaussian wave packet with energy E = 12.5 meets a square barrier of height V₀ = 20 and width 0.29, with ħ = m = 1. Inside the barrier the wave decays as e^(−κx), κ = √(2m(V₀ − E))/ħ, so the wall leaks T ~ e^(−2κw). Almost none of the packet has energy above V₀, yet 32.7 % of the probability ends up on the far side. The same exponential sets the current in a scanning tunnelling microscope and the half-life of alpha decay.

A Gaussian wave packet with energy E = 12.5 meets a square barrier of height V₀ = 20 and width 0.29, with ħ = m = 1. Inside the barrier the wave decays as e^(−κx), κ = √(2m(V₀ − E))/ħ, so the wall leaks T ~ e^(−2κw). Almost none of the packet has energy above V₀, yet 32.7 % of the probability ends up on the far side. The same exponential sets the current in a scanning tunnelling microscope and the half-life of alpha decay.

28,158 просмотров

A double integral is the limit of a sum of prisms: cut [0, π]² into n × n squares of area ΔA = (π/n)² and raise each to the height of z = sin³x sin³y at its centre. The volume is (∫₀^π sin³x dx)² = (4/3)² = 16/9 ≈ 1.7777778. The prisms give 1.7602152 at n = 4, 1.7768141 at n = 8 and 1.7777776 at n = 64, always from below. Since sin³x = (3 sin x − sin 3x)/4, the h² errors of the two waves cancel, and the gap shrinks like 7π⁴/(180n⁴).

A double integral is the limit of a sum of prisms: cut [0, π]² into n × n squares of area ΔA = (π/n)² and raise each to the height of z = sin³x sin³y at its centre. The volume is (∫₀^π sin³x dx)² = (4/3)² = 16/9 ≈ 1.7777778. The prisms give 1.7602152 at n = 4, 1.7768141 at n = 8 and 1.7777776 at n = 64, always from below. Since sin³x = (3 sin x − sin 3x)/4, the h² errors of the two waves cancel, and the gap shrinks like 7π⁴/(180n⁴).

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The curve y = ∛(x²) + 0.9 sin(kx)√(3 − x²) is a sine wave on |x| ≤ √3, carried by the cusp ∛(x²) and scaled by a semicircle. Since |sin(kx)| ≤ 1, it never leaves the band between ∛(x²) − 0.9√(3 − x²) and ∛(x²) + 0.9√(3 − x²). Those two envelopes are the heart: lobes peaking at 2.27 near x = ±1.03, a point at −0.9√3 ≈ −1.56 on the axis. Raising k only packs the wave tighter. At k = 100 it crosses the band about 110 times.

The curve y = ∛(x²) + 0.9 sin(kx)√(3 − x²) is a sine wave on |x| ≤ √3, carried by the cusp ∛(x²) and scaled by a semicircle. Since |sin(kx)| ≤ 1, it never leaves the band between ∛(x²) − 0.9√(3 − x²) and ∛(x²) + 0.9√(3 − x²). Those two envelopes are the heart: lobes peaking at 2.27 near x = ±1.03, a point at −0.9√3 ≈ −1.56 on the axis. Raising k only packs the wave tighter. At k = 100 it crosses the band about 110 times.

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Can you reverse the spin of this Penrose triangle?

Can you reverse the spin of this Penrose triangle?

50,239 просмотров

Can you reverse the spin of this hyperboloid?

Can you reverse the spin of this hyperboloid?

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A bar magnet spinning at angular speed Ω is a magnetic dipole m turning in its own plane, and it radiates at f = Ω/2π. In that plane E points straight out of it, E ∝ m̈ × r̂ at the retarded time t − r/c, so each far crest lies on θ = φ(t − r/c) + π/2: two spiral arms of pitch λ = 2πc/Ω. The whine is 1024f, ten octaves up. In empty space J = 0, so in ∇ × B = μ₀ε₀ ∂E/∂t + μ₀J only the changing E keeps B alive. The radiated power grows as Ω⁴.

A bar magnet spinning at angular speed Ω is a magnetic dipole m turning in its own plane, and it radiates at f = Ω/2π. In that plane E points straight out of it, E ∝ m̈ × r̂ at the retarded time t − r/c, so each far crest lies on θ = φ(t − r/c) + π/2: two spiral arms of pitch λ = 2πc/Ω. The whine is 1024f, ten octaves up. In empty space J = 0, so in ∇ × B = μ₀ε₀ ∂E/∂t + μ₀J only the changing E keeps B alive. The radiated power grows as Ω⁴.

23,468 просмотров

Can you reverse the spin of this sphere? Took me more than 10 seconds.

Can you reverse the spin of this sphere? Took me more than 10 seconds.

40,784 просмотров

Can you reverse the spin of this T Block?

Can you reverse the spin of this T Block?

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A sawtooth, a square and a triangle wave, each summed from its first ten nonzero Fourier terms, f(t) = ∑ bₙ sin(nt). Each term is a circle of radius |bₙ| turning n times per period. The sawtooth has bₙ = 2(−1)ⁿ⁺¹/(nπ), the square 4/(nπ) for odd n, the triangle ±8/(n²π²) for odd n. At ten terms, the square peaks at 1.18 and the sawtooth at 1.09; the triangle stays within 0.021 of exact. A jump forces coefficients like 1/n, a corner only 1/n².

A sawtooth, a square and a triangle wave, each summed from its first ten nonzero Fourier terms, f(t) = ∑ bₙ sin(nt). Each term is a circle of radius |bₙ| turning n times per period. The sawtooth has bₙ = 2(−1)ⁿ⁺¹/(nπ), the square 4/(nπ) for odd n, the triangle ±8/(n²π²) for odd n. At ten terms, the square peaks at 1.18 and the sawtooth at 1.09; the triangle stays within 0.021 of exact. A jump forces coefficients like 1/n, a corner only 1/n².

13,928 просмотров

A disk of radius a rolls on a table at tilt θ, its contact point circling at rate Ω. Gravity against the gyroscopic torque fixes Ω² = 4g/(a sin θ), with energy (3/2)Mga sin θ. Rolling resistance μ drains it as dθ/dt = −(2/3)μΩ, so near the end θ√θ falls linearly to zero: a finite-time stop. With a = 0.40 m and μ = 0.0086, θ drops from 70° to 1.4° in 15 s while Ω climbs from 1.63 to 10.08 Hz. The disk itself turns ever slower, at Ω sin θ.

A disk of radius a rolls on a table at tilt θ, its contact point circling at rate Ω. Gravity against the gyroscopic torque fixes Ω² = 4g/(a sin θ), with energy (3/2)Mga sin θ. Rolling resistance μ drains it as dθ/dt = −(2/3)μΩ, so near the end θ√θ falls linearly to zero: a finite-time stop. With a = 0.40 m and μ = 0.0086, θ drops from 70° to 1.4° in 15 s while Ω climbs from 1.63 to 10.08 Hz. The disk itself turns ever slower, at Ω sin θ.

19,220 просмотров

Can you reverse the spin of this Klein bottle?

Can you reverse the spin of this Klein bottle?

29,181 просмотров

A radius turns at a steady rate inside a regular hexagon, a decagon and a circle, and the height y = r(θ) sin θ of its tip is traced against time. For an n-gon of circumradius R with a vertex at θ = 0, r(θ) = R cos(π/n) / cos((θ mod 2π/n) − π/n). Each edge is one piece of the wave; the flat top edge is a plateau at R cos(π/n), 0.866R for n = 6, 0.951R for n = 10. As n grows the plateaus narrow and rise to R, and the wave tends to R sin θ.

A radius turns at a steady rate inside a regular hexagon, a decagon and a circle, and the height y = r(θ) sin θ of its tip is traced against time. For an n-gon of circumradius R with a vertex at θ = 0, r(θ) = R cos(π/n) / cos((θ mod 2π/n) − π/n). Each edge is one piece of the wave; the flat top edge is a plateau at R cos(π/n), 0.866R for n = 6, 0.951R for n = 10. As n grows the plateaus narrow and rise to R, and the wave tends to R sin θ.

11,905 просмотров

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Can you reverse the spin of this staircase?

matharium

25,679 просмотров • 1 месяц назад

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Can you reverse the spin of this knot?

matharium

17,157 просмотров • 1 месяц назад

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