Question about net force/acceleration/constant velocity

  • Thread starter Thread starter phosgenic
  • Start date Start date
  • Tags Tags
    Net Velocity
AI Thread Summary
An object can maintain constant velocity when the net force acting on it is zero, which occurs when all applied forces are balanced, such as a puck sliding on frictionless ice. In scenarios where forces are not equal to zero, like pushing a puck on snowy ice, the applied force must exceed friction for the puck to move, resulting in a net force that is not zero and causing acceleration. Once the applied force equals the kinetic friction, the puck can reach a constant velocity. Additionally, an object can have constant speed while changing direction, such as a car turning, which involves centripetal acceleration even if speed remains constant. Understanding these principles clarifies how Newton's laws apply in various contexts.
phosgenic
Messages
5
Reaction score
0
I read in my textbook that an object can have constant velocity when net force and acceleration are equal to 0. For an example like a puck on frictionless ice that continues to move after it has had a force applied to it that is all good and fine, I understand that inertia keeps the puck moving.

I am wondering how in an example similar to the above, the object can have constant velocity and net force can be equal to 0, with horizontally applied forces that are NOT equal to 0. For example, a puck being pushed by a hockey stick on some snowy ice, or me pushing a book across a table. Doesn't the applied force from the hockey stick or the force from my hand have to be greater than the force of friction from the ice or the table for the puck or book to move? if this is true, then net force is not equal to 0, yet the puck/book still has constant velocity and now all of Newton's principles make no sense to me. I'm hoping someone can clarify this/these concept(s).

Thanks!

EDIT: I'll add one more question here, how would you calculate (not specifically, just conceptually) the acceleration of an object that has constant speed but changing direction only?
 
Physics news on Phys.org
Welcome to PF,

phosgenic said:
I read in my textbook that an object can have constant velocity when net force and acceleration are equal to 0. For an example like a puck on frictionless ice that continues to move after it has had a force applied to it that is all good and fine, I understand that inertia keeps the puck moving.

I am wondering how in an example similar to the above, the object can have constant velocity and net force can be equal to 0, with horizontally applied forces that are NOT equal to 0. For example, a puck being pushed by a hockey stick on some snowy ice, or me pushing a book across a table. Doesn't the applied force from the hockey stick or the force from my hand have to be greater than the force of friction from the ice or the table for the puck or book to move? if this is true, then net force is not equal to 0, yet the puck/book still has constant velocity and now all of Newton's principles make no sense to me. I'm hoping someone can clarify this/these concept(s).

Thanks!

EDIT: I'll add one more question here, how would you calculate (not specifically, just conceptually) the acceleration of an object that has constant speed but changing direction only?

It seems like your question is of the form, "if I deliberately envision a scenario where Newton's laws are violated, then I find that Newton's laws aren't obeyed. What's going on?" I'm not being facetious here. I just think that contradiction is there because you put it there.

If the puck has a non-zero net force acting on it, then it will have a non-zero acceleration. That's all there is to it.
 
phosgenic said:
For example, a puck being pushed by a hockey stick on some snowy ice, or me pushing a book across a table. Doesn't the applied force from the hockey stick or the force from my hand have to be greater than the force of friction from the ice or the table for the puck or book to move?
Static friction has to be overcome to get the puck to initially move, and then kinetic (sliding) friction is involved. The puck will accelerate until the force is reduced to match kinetic friction.

phosgenic said:
I'll add one more question here, how would you calculate (not specifically, just conceptually) the acceleration of an object that has constant speed but changing direction only?
The math can be complex, but one example where this is commonly done is a car making maneuvers (turns) while at constant speed. The path can be just about any shape (spiral, parabola, hypebola, ellipse, circle, sine wave, ...) that doesn't have sharp inflection points (corners with a radius of 0).
 
Last edited:
rcgldr said:
Static friction has to be overcome to get the puck to initially move, and then kinetic (sliding) friction is involved. The puck will accelerate until the force is reduced to match kinetic friction.

The math can be complex, but one example where this is commonly done is a car making maneuvers (turns) while at constant speed. The path can be just about any shape (spiral, parabola, hypebola, ellipse, circle, sine wave, ...) that doesn't have sharp inflection points (corners with a radius of 0).

Good answer, thanks. And no, I wasn't trying to envision a scenario to violate Newton's laws. In the situation I presented they aren't violated, I just couldn't understand how they were operating in that context, as the examples that are given in my textbook/lectures are similar to the first example I gave.
 
Last edited:
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Trying to understand the logic behind adding vectors with an angle between them'
My initial calculation was to subtract V1 from V2 to show that from the perspective of the second aircraft the first one is -300km/h. So i checked with ChatGPT and it said I cant just subtract them because I have an angle between them. So I dont understand the reasoning of it. Like why should a velocity be dependent on an angle? I was thinking about how it would look like if the planes where parallel to each other, and then how it look like if one is turning away and I dont see it. Since...
Back
Top