Can you Throw a Ball Out Of Orbit?

I was just watching a video clip of astronauts space walking outside the space station and it got me thinking.....

If an astronaut that is space walking in earth orbit threw a baseball as hard as possible in the direction away from earth, would the ball eventually break free of earths gravity because of the elliptical orbit created?

Not unless he can throw the ball about 25,000 miles per hour. :O)

[edit on 8/6/2008 by DarkStormCrow]

reply to post by DarkStormCrow



Yeah, but, an astronaut floating along outside of the ISS is essentially moving at an incredible speed....upwards of 25,000MPH. So, the extra power he gives the ball is over the 25,000MPH he (and the ball) are originally going.

Right?

Cuhail

reply to post by Cuhail


Actually,
The space station travels at about 17000 mph.
So if you'd have to throw at least 8000 mph to get that ball to leave the park.

^ What he said

Actually it depends on your position in relation to the gravity field of the object you're orbiting and trying to escape, and thus the velocity required is called Escape Velocity.

That Wiki also has a list of the escape velocities required to escape the influence of the Earth, Sun, Moon, and galaxy from specific points.

So how fast can a human throw a baseball in zero/very low g might be the question also. If a pitcher can throw a ball 90 mph in 1g at sea level how fast can he throw the ball in orbit?

Is there any chance I could get a government grant to do a study? If someone can get grant money to study the mating habits of the African Blue Butterfly.....

Seriously though, I appreciate the input, but don't understand escape velocity. If there is no friction in space and the ball is already in a stable orbit, shouldn't a little shove send it away?

At 18000 mph you have enought speed to keep you from falling out of orbit and back to earth. At 25000 mph you have enough speed to actually break free of the earths gravity and break orbit, that is termed escape velocity.

reply to post by Setharoo


Even the moon only escapes earth's orbit at a rate of 3.8 cm/year.
You'd need some mighty space-roids to throw a bb out of orbit.

Think of it this way: when you throw the ball away from the Earth, the Earth's gravity is still pulling on it, slowing it down, bringing it back. There's no friction, but there's still gravity.

Escape Velocity is just a term for how fast the ball has to be going so that the Earth's gravity can't slow it down enough to bring it back.

reply to post by schrodingers dog


Thanks for the numbers. I can only assume they're accurate, or, at least more accurate than mine. I threw them out there as a guess-tamate.

What about a slingshot? I have a tennisball slingshot for my dog and I can launch a ball about 300 feet (to first contact with the ground) on a good pull @ 1g.

Cuhail

reply to post by xmotex


So "Zero Gs" is kind of deceptive isn't it? If I am in orbit I do not experience the pull of earth's gravity because the mathematical equation is balanced by the centrifugal force of my orbiting motion. If I throw the ball downward it would continue until it slows down in Earth's atmosphere. If I throw the ball upward it now has enough energy to overcome gravity PLUS a little push. I just don't see why it wouldn't keep going until the orbit was very very large and a slingshot effect takes over?

reply to post by Cuhail

Even in orbit movig at 17000 mph, there is still 99% of Earth's gravity acting on you (and your baseball). The slingshot would still need to launch the ball at an additional 8000 mph to achieve 'escape velocity'...and being in orbit won't make that slingshot move the ball any faster (I'm talking initial velocity -- say 1/10 second after leaving the slingshot) than if you "slinged" it at sea level.

reply to post by Setharoo


For the same reason satellites come down when they lose power.
Even the space station uses thrusters to stay in orbit.

I don't totally understand it, but I think what everyone is describing has to do with precession. I found a few web pages that explain that there is no perfect orbit. Precession will always decay a perfect orbit from what I understand. Unless the baseball had a rocket on it, physics would eventually slow it back down.

Originally posted by Setharoo
If I throw the ball downward it would continue until it slows down in Earth's atmosphere. If I throw the ball upward it now has enough energy to overcome gravity PLUS a little push. I just don't see why it wouldn't keep going until the orbit was very very large and a slingshot effect takes over?

A "slingshot maneuver" is where you burn fuel as you pass apoapsis, the lowest point in your orbit, of a planet that is an intermediate location between you and your destination. There's no such thing as a gravity assist maneuver in a one body situation. If you throw a ball downward directly towards the earth it will only continue "down" for a short period of time: all you did was very slightly lower the radius of the orbit at the point in the orbit where you threw your ball while raising the radius of the orbit by the same slight amount at a point in space exactly half an orbit later (basically, when the ball reaches the opposite side of the planet). You did not throw the ball towards or away from your orbital velocity vector, so you did not change the total orbital energy that the ball has, you just slightly "reshaped" the prior orbit of the ball. To eject the ball from earth's orbit you need to add enough energy along the orbital velocity vector to reach escape velocity. As mentioned before, this means adding about another 8,000mph. To deorbit the ball you need to toss it in the direction opposite of your direction of travel around the planet, and you need to lower the ball's orbital velocity enough to cause it to drop into the atmosphere. That's not a small feat either, but the exact velocity needed will depend on how high your orbit is. Eventually any object will deorbit itself from atmospheric drag, unless it's already orbiting beyond low earth orbit, but that's a natural decay and has nothing to do with your throw. It also takes a good deal of time for most orbits.

[edit on 6-8-2008 by ngchunter]

reply to post by ngchunter

To eject the ball from earth's orbit you need to add enough energy along the orbital velocity vector to reach escape velocity. As mentioned before, this means adding about another 8,000mph.

Actually, you'd need twice as much.

Enough energy to accelerate the ball from 17,000 to 25,000 miles per hour.

And an equivalent amount to accelerate the astronaut in the opposite direction, in accordance with Newton's third law of motion.

Originally posted by Astyanax
reply to post by ngchunter

 

As mentioned before, this means adding about another 8,000mph.

Actually, you'd need twice as much.

Enough energy to accelerate the ball from 17,000 to 25,000 miles per hour.

And an equivalent amount to accelerate the astronaut in the opposite direction, in accordance with Newton's third law of motion.

17,000 + 8,000mph = 25,000mph. I was only talking about the ball's velocity, not the astronaut since in this situation the astronaut is effectively the "fuel". If you throw the ball hard enough to give it 8000 mph more in its orbital velocity, then newton's third law takes over and forces you back by an equal amount of force. I believe, though, that unless you weigh the same as the ball, you will not be accelerated the same speed in the opposite direction, only by the same amount of force.

One mistake I did make in my post was the term apoapsis, should have said periapsis. That's what I get for writing too late at night.

[edit on 7-8-2008 by ngchunter]

If you throw a ball downward directly towards the earth it will only continue "down" for a short period of time: all you did was very slightly lower the radius of the orbit at the point in the orbit where you threw your ball while raising the radius of the orbit by the same slight amount at a point in space exactly half an orbit later

I remember being taught in grade school that if you throw something in space it will continue in a straight line until it reacts with something else. Why would the ball continue down for only a short period of time in the vacuum of space? Yes, I do realize "in a straight line" is a relative term.

Thanks for all of the info!

[edit on 7-8-2008 by Setharoo]

Originally posted by Setharoo

If you throw a ball downward directly towards the earth it will only continue "down" for a short period of time: all you did was very slightly lower the radius of the orbit at the point in the orbit where you threw your ball while raising the radius of the orbit by the same slight amount at a point in space exactly half an orbit later

I remember being taught in grade school that if you throw something in space it will continue in a straight line until it reacts with something else. Why would the ball continue down for only a short period of time in the vacuum of space? Yes, I do realize "in a straight line" is a relative term.

Thanks for all of the info!

The ball is never moving in a straight line - it's in orbit. It's falling around the earth at all times. You gave it a little more velocity towards the earth at THAT point in its orbit, but at a point on the OTHER side of its orbit that velocity vector points directly AWAY from the earth. Here's a diagram to help you understand: