Why does force constantly change speed of an affected by this force object? Force is counting in Newtons, and by its definition, 1 newton is the force affecting an object by the mass of 1 kg, changing the speed of this object by 1 m/s every second. I can easily make sure about that by looking on how gravity force works: the higher you are, the more speed you get falling down. And this makes me confused, because, for example, when I pull a chair for a couple of seconds then its speed is being changed only when I touch it, and after that this chair speed value is constant(equal to mine). If a chair's speed was changed, then it means that it was affected by me(in this case) with some force, but if it was a force, then the chair's speed must've been being changed constantly, getting faster and faster, because I've never stopped pulling that chair. But instead its speed is never changed, it's a constant one. Why ?
Why when gravity force works, it always changes objects speed, but when I pull a chair with some force then this chair speed is not being changed,(it's constant, as we know) ? So for now I'm confused about what force is, and when "it's force" and when it is not.
 A: You need to be careful when trying to apply the equations of physics to everyday objects. If you apply a force to drag a chair, for example, there are several factors you must take into account, as follows...

*

*Friction will resist the movement of the chair, and if the force due to friction cancels out the force you are applying to drag the chair, then the overall force on the chair will be zero and the chair will not accelerate.


*You will not have enough control over your muscles to apply a continuous constant force. If you pull a chair towards you, your arm will quickly contract to the point at which you cannot pull any further.


*If you push or pull an object so that it speeds up, you will have to start walking and then running to keep the speed increasing, but you will quickly reach a point at which you cannot run any faster, so you cannot maintain the accelerating force on the object.
So you see that there are many factors that make it hard to apply Newton's laws straightforwardly in everyday life. If you were able to apply a truly constant force to a chair then it would continue to accelerate.
A: A chair that you move by touching it, initially is accelerating as you push it.
When you let go, in the absence of any other forces the chair will move with a constant velocity as it is now not accelerating.
Why doesn't the chair move with a constant velocity you ask?
Friction. When you let go, there is a force of friction on the chair, slowing it down to a standstill.
A: An object's acceleration is determined by the net force acting upon it, not any one individual force. When you pull a chair, it slides across the floor, with friction resisting your pulling force. When the frictional force is equal and opposite your pulling force, the net force is zero and the chair does not accelerate.
This is the same principle behind terminal velocity - gravity is always pulling you down with a constant force, but when the upward force of drag/air resistance is equal and opposite to the gravitational force, you stop accelerating and fall with a constant terminal velocity.
As another example, gravity is still acting on you while you're sitting in a chair, despite the fact that you are stationary with zero velocity and zero acceleration. The normal force of the chair pushes up on you with the exact same and opposite force that gravity pulls you down, making the net force acting on you exactly zero - you don't accelerate anywhere.
