A push to an object in complete vaccum.

  • Context: Undergrad 
  • Thread starter Thread starter R Power
  • Start date Start date
  • Tags Tags
    Complete Push
Click For Summary

Discussion Overview

The discussion revolves around the behavior of an object when a force is applied to it in a complete vacuum, specifically addressing concepts of acceleration, constant velocity, and the implications of Newton's laws of motion. Participants explore theoretical scenarios involving pushing or throwing an object without friction or external forces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that an object pushed in a vacuum will either accelerate indefinitely or move at a constant speed, depending on whether the force is continuously applied.
  • One participant clarifies that if the push stops, the object will move with constant velocity, as no further work is done without an applied force.
  • Another participant questions the role of relativity in this context, suggesting limitations to the initial claims.
  • There is a discussion about the behavior of a ball thrown in a vacuum, with some asserting it accelerates while being thrown and then moves at a constant velocity once released.
  • Participants discuss the apparent acceleration of a kicked football, with one suggesting that it is a result of the player's foot decelerating rather than the ball itself accelerating after being kicked.
  • One participant emphasizes that in a vacuum, once an object is released, it will continue at the velocity it had at the moment of release, barring any external forces.

Areas of Agreement / Disagreement

Participants express differing views on the implications of force application and the resulting motion of objects in a vacuum. There is no consensus on the nuances of acceleration and constant velocity once an object is no longer in contact with a force.

Contextual Notes

Some statements rely on assumptions about the absence of external forces and the effects of gravity, which are not universally agreed upon in the discussion.

R Power
Messages
270
Reaction score
0
Hi guys
When we push an object i.e apply some force on it in complete vaccum, then due to absence of any friction; and inertia, what will happen, will the object accelerate forever because it has no reason to decelerate? Or will it move with constant speed?Why?
If the object will move forever it gives us infinite work for just a small push as input. How can this happen?:confused:
 
Physics news on Phys.org
R Power said:
Hi guys
When we push an object i.e apply some force on it in complete vaccum, then due to absence of any friction; and inertia, what will happen, will the object accelerate forever because it has no reason to decelerate? Or will it move with constant speed?Why?
If the object will move forever it gives us infinite work for just a small push as input. How can this happen?:confused:

I suspect you have a misunderstanding of Newton's laws here.

If you push and THEN stop your push, the object will move with contant velocity. If you continue to push, then the object will continue to accelerate (i.e. F=ma). So if you push on it forever, you will be doing work on it forever. If you stop pushing, and it moves with constant velocity, you are no longer doing work (work = force x distance. No force, no work!).

Zz.
 
ZapperZ said:
I suspect you have a misunderstanding of Newton's laws here.

If you push and THEN stop your push, the object will move with contant velocity. If you continue to push, then the object will continue to accelerate (i.e. F=ma). So if you push on it forever, you will be doing work on it forever. If you stop pushing, and it moves with constant velocity, you are no longer doing work (work = force x distance. No force, no work!).

Zz.
Agreed except for the limitation of relativity?
 
imagine i throw a ball, won't it accelerate?
 
R Power said:
imagine i throw a ball, won't it accelerate?
As long as you keep pushing it. But once it leaves your hand, you are no longer exerting a force on it.
 
but when players on football field kick a football, we see it accelerating even after leaving player's foot
 
R Power said:
but when players on football field kick a football, we see it accelerating even after leaving player's foot
It is not accelerating. It is accelerating relative to the player's foot due to the decelleration of the player's foot.
 
you mean to say that if in vacuum the player kicks a ball, then after kicking, players foot along with player will also move in opposite direction to that of football and so then football will move with constant velocity w.r.t player.
 
That is because there is gravity on Earth so it decelerates when it is going up and accelerates when it is going down. In a complete vacuum IN SPACE (ie no gravity) when you throw a ball the ball will accelerate from the moment you start throwing the ball till you let go of it. Once you let go of the ball the ball will continue to go at the speed it reached will accelerating in you hand, with no external forces (wether physical, electrical, magnetic, or gravitational) the ball will continue at that velocity until something hits it or applies a force on it.


FoxCommander
 
  • #10
R Power said:
you mean to say that if in vacuum the player kicks a ball, then after kicking, players foot along with player will also move in opposite direction to that of football and so then football will move with constant velocity w.r.t player.
I am saying that if a player kicks a ball in real life then it looks like the ball is accelerating away from the player due to him decellerating his foot. It is actually moving at constant velocity (ignoring gravity and friction).

If he kicks the ball in vacuum he would have no way of decelerating his own foot (without the help av gravity) so initially it would look like his foot moved with the ball but due to him having a body he would start rotating :D

It's a complicated consideration and not very intuitive. The point is as has been made in this thread an object is accelerating as long as you supply it with a force (this implies contact). Once released there can be no acceleration.
 
  • #11
That is because there is gravity on Earth so it decelerates when it is going up and accelerates when it is going down. In a complete vacuum IN SPACE (ie no gravity) when you throw a ball the ball will accelerate from the moment you start throwing the ball till you let go of it. Once you let go of the ball the ball will continue to go at the speed it reached will accelerating in you hand, with no external forces (wether physical, electrical, magnetic, or gravitational) the ball will continue at that velocity until something hits it or applies a force on it.FoxCommander
Thanx it was too clear after reading your post.
Thanx everyone!
Thread is closed.
 

Similar threads

Graduate Action and reaction when pushing an extremely long stick
  • · Replies 14 ·
Replies
14
Views
3K
Undergrad Confusion about work performed by a horizontal push or pull
  • · Replies 5 ·
Replies
5
Views
3K
High School About verification on Kinetic energy and work
  • · Replies 16 ·
Replies
16
Views
4K
Undergrad An ID-card sliding on a low friction table
  • · Replies 14 ·
Replies
14
Views
2K
Undergrad Drag equation - relative flow velocity
  • · Replies 11 ·
Replies
11
Views
4K
High School ΜStatic = μDynamic: Easier to push a moving object?
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad Work Done/Energy Transferred in One Dimensional Collision
  • · Replies 5 ·
Replies
5
Views
2K
High School Questions about momentum and force as well as normal force/friction
  • · Replies 35 ·
2
Replies
35
Views
5K
High School So, the webpage title could be: Collision Force: How is it Determined?
  • · Replies 8 ·
Replies
8
Views
3K
High School Newtons and Newton meters for pushing a weight
  • · Replies 29 ·
Replies
29
Views
6K