Cannon Physics

This is more of a question, not a debate... so I'll put it here.




A truck is moving at a constant 100mph. (<truck)

It fires a cannon in the opposite direction it is moving. (<truck(cannon>))
(the blast does not affect the velocity of the truck.)

The cannonball exits the cannon at 100mph.


Situation A- What happens to the cannonball?
Situation B- Instead of a truck, it is a spaceship (same velocities) in space, and instead of a cannonball, it is a thrown baseball. What happens to the baseball?


*Please answer for both A & B, if possible.

Huh? What do you mean "what happens to the cannonball?" How should we know? It may hit something, but there's no reason why we would know what.

If your talking about speed, the cannonball should drop to the ground I suppose. Odd question.

In space, I would assume that the ball holds still.


Again, odd questions. I suppose someone could test it if they wanted to rig a machine that fired 100 MPH projectiles, load it on a 100 MPH vehicle, and have someone else checking the velocity and outcome.

You need a lot more clarity in the question, assuming the blast does not effect the velocity of the truck, then the mass of the cannonball is zero, thus the cannonball does not exist.

If you arent satisfied with that answer, you'd need to supply more information, such as is 100mph opposite of the direction of the truck the final velocity of the cannonball? Or are you trying to describe the force applied to the cannonball? If -100mph is the final velocity, then the cannonball was launched with enough force to give it an initial speed of 200mph, because it was launched from a frame of reference that is moving in the opposite direction. If its final velocity is 100mph in the direction of the truck, then it wasn't actually launched. Because you mentioned space travel I assume you're interested in what air drag would do to the cannonball, sadly I don't have the formula offhand, but it would slow down fairly quickly, gravity would also be in effect.

If you're talking about it being fired from the cannon in the opposite direction with enough force to give it an initial speed of 100mph from rest, then the ball would simply fall to the ground.

Assuming gravity (from other celestial bodies) is not in effect, if a cannonball is launched in space, it would not experience any friction or drag forces and thus have a constant velocity after being launched. (I assume you want the velocity vector (0, 0, 0), which is still constant, just constantly zero)

Physics is hard. Try it out. Testing/Experiments > Theory.

Usually they do testing and experiments to develop a theory, so they don't have to do testing and experiments again.

But theory is good for general stuff. In specific situations, it's not as well honed because there's just too many factors to consider. So....just do it. Nike.

Okay, but if that's true, then no two experiments could really be the same. If there really are so many circumstances where things could be altered, then how could we possibly even think of generalizing one experiment and calling that experiment "Theory."

You've basically hit on skepticism. I.e. there is no a priori knowledge.

Or better yet, Hume says how do we justify the Principle of the Uniformity of Nature (Or PUN for short). Which basically says that things will be similar in the future to which they are in the past, which is a premise to every inductive argument, which means every theory as well. We know nothing, and I don't know that....

Skepticism sucks though. Soo

Given all qualities that the cannonball may have, and all qualities that the truck may have, and all qualities that the environment may have, math will tell you what occurs to a degree of precision that is probably more precise than you'd like it to be.

Kuro didn't supply enough information to really answer any sort of question, but the answer Kuro was looking for is

"Yes, if you launch a cannonball from a moving frame and the sum of the velocities of the frame and the force applied to the cannonball divided by the mass of the cannonball multiplied by the time over which the force was applied (assuming the force was constant, otherwise see Calculus) is zero, the resulting velocity will be zero and the ball will be stationary until another exterior force acts upon it, in example A, gravity, in example B, gravity as well"

Pythagoras wrote:

Given all qualities that the cannonball may have, and all qualities that the truck may have, and all qualities that the environment may have, math will tell you what occurs to a degree of precision that is probably more precise than you'd like it to be.

Kuro didn't supply enough information to really answer any sort of question, but the answer Kuro was looking for is

"Yes, if you launch a cannonball from a moving frame and the sum of the velocities of the frame and the force applied to the cannonball divided by the mass of the cannonball multiplied by the time over which the force was applied (assuming the force was constant, otherwise see Calculus) is zero, the resulting velocity will be zero and the ball will be stationary until another exterior force acts upon it, in example A, gravity, in example B, gravity as well"

[adding to the answer] From the reference frame of someone stationary to the object the truck is traveling on ( such as the earth ).



While I know that 100mph is very slow, wouldn't this still be untrue due to the Lorentz Transformation?
( For those of you who are lost: click here )

At speeds that are that low relative to one another, the precision offered should be more that sufficient to predict the motion of the cannonball. I don't even believe the Lorentz transformation would apply here, because Kuro seemed to be interested in an observer of these events from a point to which the truck's relative velocity is 100mph. If the cannonball was an observer, it would appear as though it had been suddenly (and violently) left behind bythe truck and stationary with respect to the plane that the truck was traveling on.

Please don't get all technical with this, pyth.

I know that if there was no recoil then the cannon would have weigh nothing. But that isn't the point.

Let me rephrase the question... would a ball dropped from an immobile truck look the same/similar to a ball thrown at 100mph in the opposite direction from a truck going 100mph? Would it drop like from the immobile ball, or have a similar height-vs-time qualities as a baseball thrown @ 100mph from a still position?

kuro wrote:

Please don't get all technical with this, pyth.

I know that if there was no recoil then the cannon would have weigh nothing. But that isn't the point.

Let me rephrase the question... would a ball dropped from an immobile truck look the same/similar to a ball thrown at 100mph in the opposite direction from a truck going 100mph? Would it drop like from the immobile ball, or have a similar height-vs-tieme qualities as a baseball thrown @ 100mph from a still position?

If the cannon was parallel to the plane the truck was traveling on then yes, the cannon ball would drop at the same rate as a ball dropped from a stationary position.