What is an object doing at the moment its instantaneous acceleration os zero?

Answer 1

AnswerIf we look at the problem in its most simple form, the force on an object that has zero acceleration will be zero. It takes the application of a force to change the acceleration of an object. If a force is not applied to the object, its acceleration will not be changing, and it will be zero. This fundamental idea is a necessary first step when considering basic mechanics. If a rock is in deep space (moving or at rest), and it is not acted on by gravity, its acceleration cannot be changed without applying a force. If no force is applied, its acceleration is zero. In everyday experiences, there is no such thing as zero force, even though we perceive ourselves to be in a state of zero acceleration. So we need to talk about net force.

When a body experiences zero acceleration, the net force on that object is zero, but the body may (and almost always is) still be subject to several forces, sometimes very large forces. Consider a jet aircraft that cruises in calm air, at 33,000 feet and at 600 MPH. The plane neither speeds up, nor slows down, and it nether climbs nor descends. It has zero acceleration, and so the net force on the aircraft is zero, but there are still considerable forces at play:

· Thrust is a force coming from the engines that pushes the plane forward;

· Drag is a resistive force from air friction that impedes the motion of the plane;

· Lift is the reactive force from the wings that lifts the plane up; and

· Weight is the constant force due to gravity that pulls the plane down.

In steady level flight, all these forces are in balance - thrust balances drag, and lift balances weight - but these forces are still present. The net force is zero, and so the acceleration is zero.

When standing still on the ground, you experience two forces, more if there is a wind blowing, but let's not complicate things. There is the force due to gravity pulling you toward the earth, and there is the force of the ground pushing up against your feet that offsets the force due to gravity, and so you experience a net force of zero, and thus zero acceleration.

Now let's move you up into a tree, and you are standing on a branch. Now the branch, not the ground, is exerting the force against your feet that counters the force of gravity, and so there is a net force of zero, and thus zero acceleration. Everything is fine until the branch cracks and gives way. The force due to gravity remains constant, but the force of the branch against your feet just went to zero, and so there is an unbalanced force - and acceleration due to gravity occurs. After landing on the ground safely, you have returned to a state of balanced force, and of zero acceleration.

Now consider a rock hurtling along in deep space - trillions of quadrillions of miles away from the closest star. We could consider all stars to be too far away to exert any measurable force on the rock. Only in this hypothetical example is there zero (or negligible) force on the rock, and so the rock will, in this moment, experience zero (or negligible) acceleration. Back here on earth, we must talk about zero net force.

Answer 2

An object acted on by a net force of zero has no acceleration.

Answer 3

If in motion it would be moving at a constant velocity (or it would remain at rest if never in motion in the first place).

Answer 4

If the instantaneous acceleration is zero, that means that at that moment, its velocity isn't changing.

Answer 5

It will be in uniform motion or at rest.