A student sets a block onto a rough surface and pulls the block with a constant force F directed at an angle 0 above the horizontal. The student performs several trials in which the angle O is varied, but the force F is kept constant. The acceleration is measured in each trial, and the a vs 0 shown results. The graph shows that the box only accelerates for angles between 15° and 55°, and that there is a gap in the data points when the acceleration changes from zero to non-zero values. Explain why the box does not accelerate when the angle is too small or too large, and explain the gap in the data.

A student sets a block onto a rough surface and pulls the block with a constant force F directed at an angle 0 above the horizontal. The student performs several trials in which the angle O is varied, but the force F is kept constant. The acceleration is measured in each trial, and the a vs 0 shown results. The graph shows that the box only accelerates for angles between 15° and 55°, and that there is a gap in the data points when the acceleration changes from zero to non-zero values. Explain why the box does not accelerate when the angle is too small or too large, and explain the gap in the data.