Car at 72 km/h
- Input
- 72 km/h
- Expected output
- 20 m/s
72 ÷ 3.6 = 20.
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convert km/h to m/s
Every SI kinematics formula expects speed in m/s, but road signs, speedometers and problems use km/h. There is only one conversion: divide by 3.6 to go from km/h to m/s, multiply by 3.6 to go back. The Units tab does this and shows the rule; the other fields of the calculator convert on their own.
72 ÷ 3.6 = 20.
Repeating decimal: 100 ÷ 3.6 = 27.777...
340 · 3.6 = 1224.
Convert before multiplying.
60 · 0.44704 = 26.8224.
1 knot = 1.852 km/h.
In uniform motion the velocity does not change (zero acceleration) and position grows along a straight line on the s-t graph: S = S₀ + v·t. With constant acceleration the acceleration is non-zero, velocity changes linearly, v = v₀ + a·t, and the s-t graph is a parabola: S = S₀ + v₀·t + a·t²/2. Uniform motion is the special case with a = 0. A car at a steady 72 km/h covers 100 m in 5 s; one starting from rest with a = 2 m/s² covers 25 m in the same 5 s.
The number in m/s is always smaller than in km/h, because the metre is a thousand times smaller than the kilometre but the second is 3600 times smaller than the hour. Going from km/h to m/s the value shrinks, so the operation is a division by 3.6.
Memorise that 36 km/h is 10 m/s. Then 72 km/h is double (20 m/s), 108 km/h triple (30 m/s), 18 km/h half (5 m/s). For any value, divide by 36 and multiply by 10: 45 km/h = 45/36 · 10 = 12.5 m/s.
The speed of light in a vacuum is exactly 299 792 458 m/s by the definition of the metre. Multiplying by 3.6 gives 1 079 252 848.8 km/h, about 1.08 billion km/h.
Uniform motion
Constant acceleration
Free fall and vertical
Horizontal launch
Oblique launch
Average speed
Units
= 100 m
Leave blank what you want to find. Three values are enough for constant acceleration, two for uniform motion.
Δs = v·t
Δs = v·t
Δs = 20·5 = 100
Δs = 100 mThe slope of the curve at each point is the velocity at that instant.
Area under the curve (signed) = displacement Δs = 100 m.
Area under the curve = change in velocity Δv = 0 m/s.