The force required to maintain an object at a constant speed in free space is equal to the mass of the object, the weight of the object, zero, the force required to stop it, or none of the above.
Consider a weightless string which passes through a frictionless pulley. We pull on the string to hold up a weight. We hold the string in two different positions, as shown below. Which force must be greatest? Fa Fb The two forces are equal.
Ralph told me he was thinking about the penny and feather falling in a vacuum. The penny and feather both fell at the same rate. He asked, "Does this mean that the force on the penny and the force on the feather are equal?" How would you answer his question? Be sure to explain your answer. No, the forces are not equal. Gravity pulls on the penny with more force. That's what makes the penny heavier. However, the penny also has more mass. The greater force acting on the penny does not give it a greater acceleration since it also has more mass: a=F/m.