Controlling the ball while running

Worked example 1: hard and soft first touches. A 0.43 kg ball arrives at $12\mathrm{m}{\mathrm{s}}^{-1}12\backslash ,\backslash mathrm\{m\backslash ,s^\{-1\}\}$ and is stopped. Compare the average force for a stiff foot (contact time 0.05 s) and a cushioning foot (contact time 0.20 s).

1. Change in momentum: $m\mathrm{\Delta }v=0.43\times 12=5.16\mathrm{k}\mathrm{g}\mathrm{m}{\mathrm{s}}^{-1}m\backslash ,\backslash Delta\; v\; =\; 0.43\; \backslash times\; 12\; =\; 5.16\backslash ,\backslash mathrm\{kg\backslash ,m\backslash ,s^\{-1\}\}$.
2. Stiff foot: $$F=\frac{5.16}{0.05}=103\mathrm{N}F\; =\; \backslash frac\{5.16\}\{0.05\}\; =\; 103\backslash ,\backslash mathrm\{N\}$$
3. Cushioning foot: $$F=\frac{5.16}{0.20}=25.8\mathrm{N}F\; =\; \backslash frac\{5.16\}\{0.20\}\; =\; 25.8\backslash ,\backslash mathrm\{N\}$$

Four times the contact time gives a quarter of the force. The contact times are illustrative, but the principle is exact: it is the same reason a goalkeeper's hands "give" when catching and a landing gymnast bends the knees.

Worked example 2: how far ahead? Habimana runs with the ball at $7.0\mathrm{m}{\mathrm{s}}^{-1}7.0\backslash ,\backslash mathrm\{m\backslash ,s^\{-1\}\}$ and touches it every 0.8 s.

1. Distance he runs between touches: $7.0\times 0.8=5.6\mathrm{m}7.0\; \backslash times\; 0.8\; =\; 5.6\backslash ,\backslash mathrm\{m\}$. Each push must therefore carry the ball about 5.6 m, so that it arrives back at his feet just as he reaches it.
2. Over 20 m he needs only $\frac{20}{5.6}\approx 3.6\backslash frac\{20\}\{5.6\}\; \backslash approx\; 3.6$, so four touches (see the diagram), each taken in his running stride.
3. When a defender closes in, he switches to dribbling: touches about 1.2 m apart, so that the ball is never more than one stride away.

Too short a push breaks the stride and slows him; too long a push gives the ball to a defender. Practising at speed teaches the right length.