2006-10-16 03:22:12 · 14 answers · asked by a_saranya7 1 in Science & Mathematics ➔ Physics
Imagine a cat in a cardboard box. When the cat moves inside it, the box moves too. Yet no external force (to the box) has been applied, but the box does get displaced. (don't try this at home, plz).
2006-10-16 03:25:21 · answer #1 · answered by F.G. 5 · 0⤊ 0⤋
The answerers who claim an object can move without "external force" are misleading and uninformed. Newton's Law is clear, a body at rest stays at rest unless acted on by a force and a body in motion stays in motion unless acted on by a force.
In the case of the cat in a box, the box is the body. The external force is the cat bumping into it.
The fact that the cat is inside the box does not make the cat's bump internal to the box because the box, as a body, is characterized by its mass (m). And the cat is not a part of that mass, it is external to that mass; so the force it exerts on the mass of the box is external in origin.
Re the rocket...the external force is applied to the rocket by the rapidly expanding and accelerating exhaust. But, again, that exhaust is not a part of the mass of the rocket; so it's force is external. Now the unexpended fuel on board the rocket is a part of the rocket's mass, but not the exhaust. And it's the exhaust that applies the external force.
Forces need not come from physical contact with the body. Magnetic, electrical, and gravitational forces resulting in the movement of a body are all external forces that are applied from detached sources like a magnet, a point charge, and a planet. These sources and the forces they exert are not a part of the mass that is being moved.
So the answer is, no I can't "quote some situations" because that would violate Newton's Law. And I'm a law abiding citizen.
2006-10-16 04:18:45 · answer #2 · answered by oldprof 7 · 1⤊ 0⤋
That's easy.
If you were to go to space and throw any body, it would be moving forever.
That object would cover equal displacements in equal time intervals (but it will not accelerate provided its mass remained constant) if no external force acted on the body.
For any body that is moving, there has to be a force that has acted on it in the past.
Because a body cannot change its momentum unless an external unbalced force acts on it.
However it would be possible for a body to accelerate without any external force, and that is possible if for some reason the body would lose its mass; so to conserve momentum it would accelerate.
2006-10-16 03:43:41 · answer #3 · answered by jimmy_siddhartha 4 · 0⤊ 0⤋
This is an impossible scenario! There is nowhere in the known universe where an object could exist without an external force acting on it. Gravity, no matter how small is always present. Even if it did happen, you would not be able to observe it, because the gravity of your mass would be acting on the object, no matter how powerful a telescope you were using.
qed
2006-10-22 21:56:40 · answer #4 · answered by Mez 6 · 0⤊ 0⤋
Any body continues in a state of rest or uniform motion unless acted upon by an external force. It's Newtons law. So if there is a movement there should be a force acting on it.
Work done = force x DISTANCE.
So as you mentioned the word "displayed" there should be a force acting otherwise the work done will be zero.
If you are on earth you will never be able to do this experiment because of the earth gravitational field. But again it will be done by the field's force.
A way to do it is to is to go to space and let you attracted by the gravitational field of a planet without moving.
Or if you want to make gravitational field negligible and do it with magnetic field, place a piece of iron near a magnet, you will see it move without having to apply an EXTERNAL force.
2006-10-16 03:48:55 · answer #5 · answered by IQEinsten 2 · 0⤊ 1⤋
That's how rocket ships work.
The rocket engine has the fuel inside it. Then the engine throws the fuel out very fast. The fuel goes off in one direction, and the engine goes in the other direction.
Now, you might say I have cheated in this answer. The engine is displaced, yes. But if you consider the engine and the fuel together as one object, then the center of mass has not moved. Even though the engine and fuel get farther away from each other, the combined system has not moved its center of mass, and in that sense has not been displaced.
2006-10-23 02:19:19 · answer #6 · answered by old c programmer 4 · 0⤊ 0⤋
Rocket in space. The burning fuel ejected pushes the rocket forward - no external force.
2006-10-16 03:25:30 · answer #7 · answered by amania_r 7 · 0⤊ 0⤋
I didn't think that was possible. A body at rest will not move without a force acting upon it? Or have I got something wrong?
2006-10-16 03:24:48 · answer #8 · answered by mark 7 · 0⤊ 0⤋
confident!! yet in a typica;l way. fix that merchandise and you initiate up shifting with an accnleratin. the item has displaced in ur reference physique. certainly, forc is often could desire to displace a physique. artwork achieved on a physique canm be 0 ( whilst tension and dispalcement are perpendicular like in a circle) yet frce can in no way be 0.
2016-12-13 09:14:32 · answer #9 · answered by ? 4 · 0⤊ 0⤋
external? a firecracker... but even then you have to light it... so no.. i dont think its possible... if an "object" had within it the capability to react or produce a force , it would have already done so... unless it required something to trigger it. and that would be the external force.. so id say it never happens..
2006-10-23 16:23:31 · answer #10 · answered by Anonymous · 0⤊ 0⤋