# The Naked Scientists Forum

### Author Topic: If an object is moving through space and no force is applied, where does it go?  (Read 2947 times)

#### Harri

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##### If an object is moving through space and no force is applied, where does it go?
« on: 18/10/2015 21:28:37 »
Hi all, is it true that an object set into motion in outer space will travel in a straight line until a force alters it's direction? If the object never meets another force where will it end up?
« Last Edit: 18/10/2015 23:40:29 by chris »

#### alancalverd

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##### Re: Into infinity?
« Reply #1 on: 18/10/2015 22:47:09 »
Somewhere else.

#### jeffreyH

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #2 on: 18/10/2015 23:41:17 »
The restaurant at the end of the universe.

#### PmbPhy

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #3 on: 19/10/2015 03:35:00 »
Hi all, is it true that an object set into motion in outer space will travel in a straight line until a force alters it's direction? If the object never meets another force where will it end up?
Simple. Just apply Newton's First Law. A body which is at rest remains at rest and a body which is motion will remain in motion unless its affected by by an external force.

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#### Harri

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #4 on: 19/10/2015 22:08:32 »
Hi and thanks for the reply.

What I was trying to clarify was if the object just carries on until it meets an external force then the actual atmosphere around the object can't offer any resistance! So what does the actual atmosphere consist of?

#### Colin2B

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #5 on: 19/10/2015 22:36:27 »
So what does the actual atmosphere consist of?
That depends on the object. I assume you are thinking of a planet, so it would depend on the type of planet, earth type? Mars type? You choose.

then the actual atmosphere around the object can't offer any resistance!
Can't offer any resistance to what?
If it is a planet moving it would require a very large force to alter it's momentum and the atmosphere might not be the main consideration.

Can you clarify what sort of object and scenario you are thinking about.

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#### Thebox

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #6 on: 20/10/2015 08:28:21 »
Hi all, is it true that an object set into motion in outer space will travel in a straight line until a force alters it's direction? If the object never meets another force where will it end up?

Hi Harri, yes it true that an object in motion will remain in motion and at a constant velocity unless effected by external forces. Imagine a cannon ball being fired from a cannon, on earth the cannon ball follows a curved path by the force of the gravity of the earth pulling and acting on the cannon balls kinetic energy slowing the cannon ball down, also there is added resistance of the gaseous atmosphere.
However if we apply some Physics and increase the kinetic energy (Ke) of the cannon ball, i.e more gunpowder in the cannon and a bigger cannon/longer barrel, then we increase the potential energy increasing the Ke applied to the ball.  The ball will then have enough speed and acceleration to travel a straighter path (linearity), eventually leaving the earth's orbit. space itself then offers no resistance to the cannon ball, only when the ball gets caught again by a gravity trap will the ball start to curve, hence planetary orbits.

regards

steve

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#### Harri

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #7 on: 20/10/2015 08:48:20 »
Hi Colin and Steve, if instead of a planet we use the cannon ball as an example, and take that cannon ball up to the space station, and just 'shove' it off into space, from what I now understand the atmosphere in space wouldn't offer any resistance to the ball and it would just keep traveling in a straight line.

I am an early years teacher and we have lots of fun rolling a truck down a ramp and measuring how far it goes. We change the angle of the ramp, we increase/decrease the weight in the truck, we change the floor surfaces, we estimate how far the truck will go, and then check the results, and determine why we get different distances traveled.

Now you know the level at which my brain is functioning here ! The questions the ball in space raises for me are: the atmosphere in space offers no resistance at all? What is the actual atmosphere made of? Is it gases? Don't gases offer resistance?
And if this ball avoids gravitational pulls where exactly does it end up? There is no end to space?

#### Thebox

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #8 on: 20/10/2015 18:29:08 »
Hi Colin and Steve, if instead of a planet we use the cannon ball as an example, and take that cannon ball up to the space station, and just 'shove' it off into space, from what I now understand the atmosphere in space wouldn't offer any resistance to the ball and it would just keep traveling in a straight line.

I am an early years teacher and we have lots of fun rolling a truck down a ramp and measuring how far it goes. We change the angle of the ramp, we increase/decrease the weight in the truck, we change the floor surfaces, we estimate how far the truck will go, and then check the results, and determine why we get different distances traveled.

Now you know the level at which my brain is functioning here ! The questions the ball in space raises for me are: the atmosphere in space offers no resistance at all? What is the actual atmosphere made of? Is it gases? Don't gases offer resistance?
And if this ball avoids gravitational pulls where exactly does it end up? There is no end to space?

Hello again,  firstly when angling a ramp, the greater the angle the greater potential energy,and a greater Kinetic energy (Ke) is gained by the truck , the ''weight'' of the truck stays the same and is referred to as Newtons of force not to be mistaken for mass which is defined in kilograms (kg).
Generally people refer to mass as weight a common mistake.
Changing the floor surfaces changes the friction imposed on the truck tyres, i.e ice has a low friction, less grip, less friction.

The atmosphere of earth contains gases, these gases do offer resistance, we call these gases such as air, a medium, space does not have a medium so offers no resistance to the cannon ball.

#### Harri

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #9 on: 20/10/2015 19:28:19 »
Hi, wow, all that space exists BUT all that space has no medium! A layman's question I guess, but how can something exist if it doesn't have a medium?

#### Thebox

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #10 on: 20/10/2015 22:25:24 »
Hi, wow, all that space exists BUT all that space has no medium! A layman's question I guess, but how can something exist if it doesn't have a medium?

It exists as space for the very reason it has no medium, if it had a medium it would be called an atmosphere rather than space. Space exists as space and things of existence, exist in that space.

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#### Colin2B

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #11 on: 20/10/2015 23:00:04 »
?...from what I now understand the atmosphere in space wouldn't offer any resistance to the ball and it would just keep traveling in a straight line.
Strictly speaking there is a very slight atmosphere in space, but it is very, very slight- around one hydrogen atom for each meter cube, that is effectively a vacuum. So there is no air resistance or friction. To all intents and purposes space is infinite, but any object travelling through space is likely to encounter debris, asteroids, dust and eventually another galaxy.

I am an early years teacher and we have lots of fun rolling a truck down a ramp and measuring how far it goes. We change the angle of the ramp, we increase/decrease the weight in the truck, we change the floor surfaces, we estimate how far the truck will go, and then check the results, and determine why we get different distances traveled.
That sounds like great fun, lots of opportunities for weighing, measuring and trying to predict what might happen. Keep up the good work.

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#### Harri

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #12 on: 21/10/2015 10:40:26 »
My questions have run their course I think, thanks.

I no longer teach early years pupils. I now teach post 16 students who have special needs. But, nothing compares to showing a little brain something for the first time. A cork floating, a stone sinking, ice melting, puddles disappearing/evaporating ... it's a bit like parenting but you have 30 children !

#### evan_au

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #13 on: 21/10/2015 11:34:08 »
Quote from: Harri
is it true that an object set into motion in outer space will travel in a straight line until a force alters it's direction?
One aspect that has not really been addressed: When you are near a massive object like the Earth or the Sun, gravity provides a force that attracts the two, changing both their paths. (Although the change in motion of the Sun would be very small and hard to measure for any object smaller than a planet.)

Quote
take that cannon ball up to the space station, and just 'shove' it off into space... it would just keep traveling in a straight line.
The space station is in orbit around the Earth, taking about 90 minutes to go around once. The Earth's gravitational field bends the path of the space station into a circle.

If you shove a cannonball off the space station, the cannonball will also be in orbit around the Earth, also taking about 90 minutes for one complete circuit.

If you gave it a really big shove (with a powerful rocket), you could take it out of Earth orbit, and into orbit around the Sun. It would take about 1 year for an orbit around the Sun.

Quote
from what I now understand the atmosphere in space wouldn't offer any resistance to the ball
The very thin atmosphere at the height of the ISS does provide some drag, causing it drop in altitude every month. To avoid the ISS crashing back to Earth while it is still in use, they use a rocket to boost its height every month or so.

A solid cannonball is denser than the hollow ISS, so it would take longer to crash, but it would eventually hit the thicker part of the atmosphere, forming a little fireball as it plummeted towards Earth.

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#### syhprum

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##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #14 on: 21/10/2015 12:22:03 »
This is really a question about the geometry of space , if it is flat it goes off to infinity if it is curved it comes back to where it started but what if it is saddle shaped where does it go then ?
« Last Edit: 21/10/2015 12:24:02 by syhprum »

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#### The Naked Scientists Forum

##### Re: If an object is moving through space and no force is applied, where does it go?
« Reply #14 on: 21/10/2015 12:22:03 »