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LorentzLen
Objects shrink in the direction of motion — see by how much at any speed.
A moving object's length in the direction of motion is contracted: L = L₀/γ, where L₀ is the proper length (measured at rest) and γ is the Lorentz factor. At 86.6% c, γ = 2, so the object appears half its rest length. This isn't an optical illusion — it's a real consequence of spacetime geometry.
Length contraction is negligible at everyday speeds. Even the ISS at 7.7 km/s has γ ≈ 1.0000000003. But for particles in accelerators moving at 99.999% c, contraction is dramatic — a 1-meter rod would measure just 4.5 mm. Muons from cosmic rays survive to reach Earth partly because of their contracted travel distance.
Contracted length
43.589 m
What you entered
v/c (velocity as fraction of speed of light)
0.9= 0.9cv² / c²
0.9²= 0.81Lorentz factor: γ = 1 / √(1 − v²/c²)
1 / √(1 − 0.81)= 2.2942Contracted length: L = L₀ / γ
100 / 2.2942= 43.589 mResult
Contracted length: 43.589 m
At 90.0% the speed of light, a 100 m object contracts to 43.589 m along the direction of motion — an observer moving with the object still measures 100 m.