Question

Some results of simple physics experiments conducted on planet Earth are not intuitive. Examples include determining the acceleration of a ball tossed upwards at the point when its instantaneous vertical velocity is zero, and the time it takes two balls to hit the ground when they are tossed off the same horizontal surface at different initial horizontal velocities. Discuss each of these results and provide the reasoning that explains the apparently non-intuitive outcomes.

Answer 1

1] When the ball is tossed upwards, the ball slows down until it reaches its highest point where its velocity becomes zero. Intuitively, one expects that since the velocity is zero here, the rate of change of velocity, which is acceleration, is also zero at this point. However, that is not true. The acceleration is always the acceleration due to gravity regardless of where the ball is and it acts towards the Earth's center. Here, the acceleration is not a result of the change in velocity. Rather, the change in the velocity is due to the acceleration.

2] When two balls are launched from the same horizontal surface but with different horizontal velocities, intuitively one expects the faster ball to reach the ground earlier. However, that is not the outcome. Since both are released from the same height, their vertical velocities (which are initially zero) are equal thereby implying that the time it will take for both to reach the ground will be same. Though, the ball with a larger horizontal velocity will travel a larger horizontal distance in the same time.