To demonstrate the law of conservation of momentum using two billiard balls, set up a frictionless surface (such as a smooth table) and place one ball (Ball A) stationary and the other (Ball B) moving towards it with a known velocity. Measure the mass of both balls, typically around 0.16 kg for a standard billiard ball. Upon collision, measure the velocities of both balls after the collision using a high-speed camera or a motion sensor.
For example, if Ball A (mass = 0.16 kg) is initially at rest and Ball B (mass = 0.16 kg) strikes it with a velocity of 2 m/s, the initial momentum is \( m_B \cdot v_B = 0.16 , \text{kg} \cdot 2 , \text{m/s} = 0.32 , \text{kg m/s} \). After the collision, measure the resulting speeds (e.g., Ball A moves at 1 m/s and Ball B at 1 m/s). The total final momentum will be \( (m_A \cdot v_A) + (m_B \cdot v_B) = (0.16 \cdot 1) + (0.16 \cdot 1) = 0.32 , \text{kg m/s} \). This confirms that momentum is conserved, as the total momentum before the collision equals the total momentum after the collision.