# Illustration Head-on Elastic Collision of Two Equal Masses

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Head-on elastic collision of two balls of the same mass $$m$$. Before the collision, the first (red) ball has the velocity $$v_1$$ directed to the right. The second (blue) ball has the velocity $$v_2$$ to the left. The two balls collide head-on and fly apart again. The first ball then has the velocity $$v'_1 = v_2$$ and the second ball has the velocity $$v'_2 = v_1$$.

In an elastic head-on collision between two identical balls, the balls exchange their velocities. After the collision, the red ball has the same velocity as the blue ball before the collision. And the blue ball has after the collision the velocity of the red ball before the collision.