If a body is moving at a constant speed and no external force is acting on it, it shud continue to move thus?

Question

forever, according to Newton's 1st law. But for this, the body needs energy. How can a body possibly have enough energy to last till eternity?

Answer 1

It takes energy to accelerate or decelerate. Once moving it will continue in a straight line forever if there are no external forces.

Answer 2

You said, "....but for this, the body needs energy." This is incorrect. An object needs energy to start moving. No energy is required to keep it moving. The reason for your incorrect assumption is that all the moving objects you are familiar with here on earth have an opposing force continually slowing them down. This force is called friction. If you start a ball rolling across the floor it will eventually slow down and stop - NOT because the ball requires energy to keep moving but because every molecule in the floor acts as an opposing force just as if each molecule were a tiny person pushing on the ball in the direction opposite to its motion. If the ball were in outer space where it is unlikely to encounter an opposing force it would continue to move indefinitely in the same direction just like old Isaac said. Did you ever wonder how rockets carry enough fuel to get to, say, Jupiter? They don't. They carry enough fuel to get them out of the earth's atmosphere where they encounter air resistance (a kind of friction) and from then on they continue to move in the same direction courtesy of Newton's first law first part. The only additional fuel they need is enough to make mid-course corrections in their flight path. Remember, the second part of the first law of motion says that energy is required to change either speed or direction.

Answer 3

If no external force is acting on it, then, yes, it should continue to move.

Of course, in the real world there are always external forces acting and due to the energy consumed to continue to move against many of these forces the body will eventually come to a stop.

Answer 4

It cannot move at a constant speed on its own because of forces that work against it. One of which is friction. The body only has enough energy that was originally put against it to produce the unbalanced force that caused it to move in the first place.

Answer 5

That is the difference between reality and theory. IN your practical experiece, such a body eventially stops, dur to friction...but that is the dilemma...friction is an external force acting against the body.

In space, onc a body is given momentum, it is virtually frictionless and will move perpetually...so that is when satellites stay up a long time (they do encounter some atmosphere and friction). We call that energy kinetic energy...- mv^^2

Answer 6

ur right...according to newton's law....a body that is at rest or in motion tends to stay at rest or in motion unless some other body stops it or exerts some kind of force on it.
a body at rest can stay at rest for all eternity.
but an object in motion has some kind of energy that is pushing it along. that energy has to finish one day. it won't last for all eternity. and till the energy finishes, the body will continue in motion.
newton's law does not mention 'eternity'

Answer 7

No problem, you have an example in our planet it is spinning since 4,5 billion years ago. This planet has no external forces acting on it, so the spinning will continue for a long time from now.
Also is the application of the conservation of energy principle.

Answer 8

It only takes energy to start the motion, after that it will continue to move unless air resistance, gravity, friction, or some other force acts against it.

Answer 9

With no force acting against it it only needs energy to begin moving.

Answer 10

well there is no such enviroment where there is absolutly no force acting against anything. even in space you have gravitional fields of large magnitude, solar winds, magnetic fields, light, and many more, however despite this look at the commets that we see and have been around or even our planet, note the elicptical orbit in referance to the other planets, not their orbits but position of the planets. This acts like a slingshot where we leave one field of gravity or magnetic field we soon pass into another, so we slow down speed up rotate axis,ect. The same applys to atoms and electrons, thats why they breakdown and decay.