Because if we look at the graph of a linear fit, how would you interpret the x-intercept and the y-intercept?
The answer is YOU CAN'T. Because in real life, there is never going to be a point when the mass of an object equals 0 N, as long as this object is on earth, it experiences a gravitational force. There's no exception. On the other hand, when the graph hits the x-axis where acceleration=0 m/s/s, for a linear fit, the graph will keep going into negative accelerations. In the set-up for this specific experiment, it is not impossible for an object to acceleration backwards or experience a negative acceleration on its own. For those reasons, the graph cannot cross the x-axis nor the y-axis, therefore no x or y-intercept are allowed to be on the graph for this particular experiment.
And this is what we call the Boundary Conditions.
The answer is YOU CAN'T. Because in real life, there is never going to be a point when the mass of an object equals 0 N, as long as this object is on earth, it experiences a gravitational force. There's no exception. On the other hand, when the graph hits the x-axis where acceleration=0 m/s/s, for a linear fit, the graph will keep going into negative accelerations. In the set-up for this specific experiment, it is not impossible for an object to acceleration backwards or experience a negative acceleration on its own. For those reasons, the graph cannot cross the x-axis nor the y-axis, therefore no x or y-intercept are allowed to be on the graph for this particular experiment.
And this is what we call the Boundary Conditions.