Isnt zero a constant? What is the confusion here?Mathivanan said:Some texts say the body is moving with zero acceleration and others say it is moving with constant acceleration.
The confusion is: what is the need for qualifying acceleration as constant; it is positive or negative or zero, in all these cases it's a constant.Dale said:Isnt zero a constant? What is the confusion here?
Inaction and action are both actions, right!Ibix said:We do tend to make a distinction between "not doing something" and "doing something" in natural language. But maths regards it as a distinction without a difference. So, as others have noted, zero is just a constant like any other.
Acceleration need not be constant. A simple example is a spring and simple harmonic motion. The acceleration varies over time, it is not constant.Mathivanan said:The confusion is: what is the need for qualifying acceleration as constant; it is positive or negative or zero, in all these cases it's a constant.
Mathivanan said:The confusion is: what is the need for qualifying acceleration as constant; it is positive or negative or zero, in all these cases it's a constant.
No. Constant acceleration means ##da/dt=0##. That is satisfied by any ##a##, zero or non-zero, that does not vary with time.boringelectron said:Constant acceleration can not be zero
This isn't right. A body moving at constant velocity has zero acceleration, whether it's moving at zero velocity or at hundreds of metres per second.Mathivanan said:What I thought is: a body is said to have zero acceleration when it is either at rest or comes to rest if it's moving; it is because acceleration due to gravity.
Think of a car at rest. Unless a force acted upon, it cannot move. When you apply force it starts moving against acceleration due to gravity. Depending upon the change in this initial acceleration, the car keeps moving or comes to rest.Ibix said:This isn't right. A body moving at constant velocity has zero acceleration, whether it's moving at zero velocity or at hundreds of metres per second.
Our every day experience is that stuff that is moving slows down and stops. But this is actually an oddity of being on the Earth in an atmosphere where there are always frictional forces (with the air or the ground) that try to make you move the same way the ground is moving. You need to separate two concepts in your mind: one is that you will always move in a straight line at a constant velocity unless forces act (that's Newton's first law). The other is that (in the circumstances that happen to be true on the Earth) there are always forces acting unless you are stationary with respect to the surface of the Earth.
Mathivanan said:Think of a car at rest. Unless a force acted upon, it cannot move. When you apply force it starts moving against acceleration due to gravity. Depending upon the change in this initial acceleration, the car keeps moving or or comes to rest.
More precisely, it cannot start moving without a force if it is initially at rest.Mathivanan said:Think of a car at rest. Unless a force acted upon, it cannot move.
Really? The acceleration due to gravity is directed vertically downwards. Unless you have a flying car, you are not correct here. The car has to work against friction to move relative to the Earth and air.Mathivanan said:When you apply force it starts moving against acceleration due to gravity.
No. The car will always come back to rest, but this is because of friction. This is the point I was talking about separating in your mind: the car will continue to move at the same speed as long as no force acts on it. But on the Earth there will always be a force acting on it as long as ot moves with respect to the surface of the Earth.Mathivanan said:Depending upon the change in this initial acceleration, the car keeps moving or or comes to rest.
Therefore, the car is at rest due to friction and not due to Earth's gravity.Ibix said:More precisely, it cannot start moving without a force if it is initially at rest.
Really? The acceleration due to gravity is directed vertically downwards. Unless you have a flying car, you are not correct here. The car has to work against friction to move relative to the Earth and air.
No. The car will always come back to rest, but this is because of friction. This is the point I was talking about separating in your mind: the car will continue to move at the same speed as long as no force acts on it. But on the Earth there will always be a force acting on it as long as ot moves with respect to the surface of the Earth.
I began with v=u+at and still continuing with that.ZapperZ said:This is wrong at the elementary level. A force that typically causes a car to move is PERPENDICULAR to the direction of gravity. So the force isn't applied to overcome gravity, but rather because of friction and to overcome inertia.
Now, if you start lifting the car up vertically, then yes, you are opposing the weight of the car, but this isn't how a car normally moves.
I still don't know if you're still asking your original question or whether you've moved on to a different topic. It isn't clear if you've understood the explanation you've been given on your original question.
Zz.
Mathivanan said:I began with v=u+at and still continuing with that.
Not quite. It moves at the velocity it is moving at because it was already moving at that velocity. If some force pushes it into changing its motion then, on the surface of the Earth, a frictional force will always appear to resist any motion relative to the surface.Mathivanan said:Therefore, the car is at rest due to friction and not due to Earth's gravity.
I think your problem is distinguishing between forces and accelerations.Mathivanan said:I began with v=u+at and still continuing with that.
What is precisely 'oddity of being on the Earth'?Ibix said:This isn't right. A body moving at constant velocity has zero acceleration, whether it's moving at zero velocity or at hundreds of metres per second.
Our every day experience is that stuff that is moving slows down and stops. But this is actually an oddity of being on the Earth in an atmosphere where there are always frictional forces (with the air or the ground) that try to make you move the same way the ground is moving. You need to separate two concepts in your mind: one is that you will always move in a straight line at a constant velocity unless forces act (that's Newton's first law). The other is that (in the circumstances that happen to be true on the Earth) there are always forces acting unless you are stationary with respect to the surface of the Earth.
The oddity of being on the Earth is that you're surrounded by matter in large quantities, and if you want to move relative to it you need to work to push it out of the way. That isn't anything to do with motion in its own right. Separating the concepts of "moving" and "having to shove the air out of the way if you want to move relative to it" was one of Newton's great insights (edit: or Galileo's I suppose, although Newton developed the concept into his laws of motion).Mathivanan said:What is precisely 'oddity of being on the Earth'?
I like that:surrounded by matter in large quantities.Ibix said:The oddity of being on the Earth is that you're surrounded by matter in large quantities, and if you want to move relative to it you need to work to push it out of the way. That isn't anything to do with motion in its own right. Separating the concepts of "moving" and "having to shove the air out of the way if you want to move relative to it" was one of Newton's great insights (edit: or Galileo's I suppose, although Newton developed the concept into his laws of motion).
Apple fell down from the tree due to Earth's gravity. I could pick that apple because of frictional force, otherwise it should have gone down to the center of earth.Ibix said:Not quite. It moves at the velocity it is moving at because it was already moving at that velocity. If some force pushes it into changing its motion then, on the surface of the Earth, a frictional force will always appear to resist any motion relative to the surface.
Relevance, please?Mathivanan said:Apple fell down from the tree due to Earth's gravity. I could pick that apple because of frictional force, otherwise it should have gone down to the center of earth.
You seem to be confusing acceleration and velocity. What you wrote is completely false. It would be essentially correct to say "a body is said to have zero velocity when it is either at rest or comes to rest if it's moving"Mathivanan said:What I thought is: a body is said to have zero acceleration when it is either at rest or comes to rest if it's moving;
Yes. If a=0 then it moves at constant speed in a straight line per Newton's first law. Such motion is called "inertial".Mathivanan said:In the equation v=u+at, when a=0, the body moves with a constant velocity. Can we say that the body is moving with zero acceleration? If it is how a body can move with constant velocity without acceleration.
This is not correct. Also, a is a vector so the designation of "positive acceleration" doesn't even make sense generally.Mathivanan said:It should have a positive acceleration to move with constant velocity. Hence 'a' cannot be zero.
Yes, your understanding is wrong. The "a" is simply acceleration. Your belief that a body cannot be moved without acceleration is wrong. A body cannot be moved without velocity, but velocity can be nonzero while acceleration is zero. Again, such motion is called "inertial".Mathivanan said:Therefore, there is something wrong with my understanding. In the equation, 'a' is not simply acceleration but rather a change in acceleration or Δa. As a body cannot be moved without acceleration
Has the driver taken off their leg from the accelerator?jbriggs444 said:Relevance, please?
A car moving down the highway at 50 miles per hour subject to zero net force will have a constant acceleration of zero despite the fact that it is not at rest in the ground frame.
You need a force to move a body and that force is mass*acceleration.Dale said:You seem to be confusing acceleration and velocity. What you wrote is completely false. It would be essentially correct to say "a body is said to have zero velocity when it is either at rest or comes to rest if it's moving"
Yes. If a=0 then it moves at constant speed in a straight line per Newton's first law. Such motion is called "inertial".
This is not correct. Also, a is a vector so the designation of "positive acceleration" doesn't even make sense generally.
Yes, your understanding is wrong. The a is simply acceleration. Your belief that a body cannot be moved without acceleration is wrong. A body cannot be moved without velocity, but velocity can be nonzero while acceleration is zero. Again, such motion is called "inertial".
No, you don't. See Newton's first law.Mathivanan said:You need a force to move a body.
I said zero net force. Can you tell us what that means?Mathivanan said:Has the driver taken off their leg from the accelerator?
Dale said:Isnt zero a constant? What is the confusion here?
Just taking your statement one piece at a time.Mathivanan said:What I thought is: a body is said to have zero acceleration when it is either at rest or comes to rest if it's moving; it is because acceleration due to gravity.