- #1
Click For Summary
Homework Help Overview
The discussion revolves around identifying the forces acting on a ball at different points labeled A, B, C, and D. Participants are exploring the effects of gravity and other forces, particularly in the context of whether air resistance is relevant.
Discussion Character
- Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants discuss the forces acting on the ball, particularly at points A and B, questioning the role of gravity and the relevance of air resistance. Some express confusion about the ball's upward motion despite gravity acting downwards.
Discussion Status
The discussion is ongoing, with participants examining different interpretations of the forces involved. There is a focus on clarifying assumptions about air resistance and the conditions under which the forces are being analyzed.
Contextual Notes
Some participants note that the original poster did not specify the presence of air resistance, leading to varying interpretations of the forces acting on the ball. It is mentioned that the scenario may be in a vacuum, which influences the discussion on gravitational force alone.
- #2
NascentOxygen
Staff Emeritus
Science Advisor
Homework Helper
- 9,253
- 1,080
What forces do you think are acting on the ball at A?
- #3
Jirya
- 9
- 0
Of course, the gravitation force and a force from the 'table'. The force from the table is greater; and that means that the ball jumps up.
But actually, I'm just interested to know which forces are acting between A and B. A friend of my claim that only the gravitation force is acting. Is that true?
But actually, I'm just interested to know which forces are acting between A and B. A friend of my claim that only the gravitation force is acting. Is that true?
- #4
adjacent
Gold Member
- 1,552
- 62
What about the force when moving through air?Jirya said:
- #5
Jirya
- 9
- 0
adjacent said:
I don't see how that's relevant here? :)
- #6
adjacent
Gold Member
- 1,552
- 62
Yes.If your question says air resistance is negligible,it's not relevant.Jirya said:
However,in the OP, you said that you want to know the forces acting on the ball.
You did not say that there's a vacuum there.
Still,there's another force.Think of why the ball is slowing down.Energy is transformed from kinetic to another form.We know that it's not potential energy,soo...
- #7
Jirya
- 9
- 0
adjacent said:Yes.If your question says air resistance is negligible,it's not relevant.
However,in the OP, you said that you want to know the forces acting on the ball.
You did not say that there's a vacuum there.
Still,there's another force.Think of why the ball is slowing down.Energy is transformed from kinetic to another form.We know that it's not potential energy,soo...
Yeah, it's in vacuum. My mistake. I should have informed that.
... What are you implying? :-D
- #8
adjacent
Gold Member
- 1,552
- 62
Jirya said:
Oh sorry.I forgot that you only want the forces acting between A and B.
If the place is a vacuum,then the force(s) acting between A and B is Gravity alone.You're right.
- #9
Jirya
- 9
- 0
adjacent said:
But why is the ball moving up then?
If only gravity works alone you could imagine that the ball should move downwards?
- #10
adjacent
Gold Member
- 1,552
- 62
Jirya said:
Where is it moving up? It's moving down after some time.
It's actually accelerating downwards. ##\vec F=m\vec a##
A force only accelerated an object in some direction.It does not mean that if you have a force downwards,it should move only downwards.
Think of this: If you throw a ball upwards,why does it move up for sometime instead of falling the moment you release it?
- #11
adjacent
Gold Member
- 1,552
- 62
(Think of this: thing)
At the moment you release the ball,the only force .i.e gravity, is acting downwards.It will then accelerate it downwards(Decreasing the upward velocity).When the upward velocity becomes zero,it stops moving up and starts to fall down.
At the moment you release the ball,the only force .i.e gravity, is acting downwards.It will then accelerate it downwards(Decreasing the upward velocity).When the upward velocity becomes zero,it stops moving up and starts to fall down.
Last edited:
- #12
Govind_Balaji
- 83
- 0
Think of Newton's laws
- #13
Rellek
- 107
- 13
Are we assuming no air resistance?
- #14
adjacent
Gold Member
- 1,552
- 62
Govind_Balaji said:
How is Newton's laws going to help here?
-His first law is not useful here because there is an external force acting(Gravity)
-His second law will work but we don't need it here because a is 10m/s^2 or 9.81m/s^2(Depending on the amount of accuracy required)
-His third law will not work here because it's not touching anything.
Note that Jirya wants the forces acting between A and B.
Yeah.Read the posts carefully.Rellek said:
Jirya said: