I'm sure I'm wrong though.
Are they saying that the ball would ricochet off of the train? Got a link to the article? The entire gravity assist thing is absolutely amazing math to me.
Likewise, when a golf ball is hit by a golf club, the speed of the golf ball should be roughly 1.5 times that of the speed of the swing of the club head. This increase in speed is due to the elasticity component of the golf ball.
I know, it's a miracle....
If you are on a train traveling 80kph and throw a ball at 30kph in the direction of travel, to other passengers on the train the ball travels 30kph, to someone standing on the platform in the station the ball travels at 110kph.
If you throw the ball in the opposite direction of travel of the train, to the passengers the ball travels 30kph, but to the guy standing on the platform in the station, the ball travels 50kph in the direction of travel of the train.
It's pretty straightforward... until you accelerate the speed of the train to a crazy speed and instead of throwing a ball, you turn on a flashlight. Special relativity causes time to slow down at higher speeds and the speed of the light is constant whether you are on the train or in the station.
Keep movin'. You'll live longer relative to everybody else.
The author of the article (it would help to read it) seems to be using concepts of kinetic energy to describe gravitational assist. The weight of the object matters in both examples, but they are two entirely different physical phenomena. A tennis ball could very well bounce off a train at 130 kph based on the elasticity of the Ball and the weight of the train (it would bounce off a car traveling at 80 kph at a much slower speed than it would a train).
Regardless, sounds like the example was concocted by a journalist and not a scientist!
So... frame of reference still comes into play.
In an elastic collision, a ball will bounce off a wall with the same speed that it was thrown at the wall. Imagine that you're in the locomotive. Your frame of reference is essentially the front of the train. Which is our wall.
The train is moving 80kph to the left. The ball is thrown 30kph to the right. In your frame of reference, the ball is approaching you and the wall at 110kph... (80kph + 30kph) and since this is an elastic collision, it will rebound from your frame of reference at 110kph away from you in the direction of travel of the train... but your frame of reference is moving 80kph away from the guy on the platform who sees the ball fly off at 190kph... not 130kph.
... but from a fixed point in space, the Earth is rotating on its axis and orbiting the sun. So it could actually all be moving backwards...
Amoebus's Link
"Another analogy, illustrated by the cartoon at right, involves a moving railroad train that represents Jupiter, moving along its track about the Sun. The kid in the propeller beanie throws a tennis ball that represents a spacecraft. It encounters the train, which transfers its momentum into the ball.
It's interesting to note the speeds in the cartoon. The propeller-beanie kid sees his tennis ball moving away from him at 30 miles per hour. So does the Sun, sitting on the stationary platform. The engineer driving the train sees the ball coming at about 80 MPH, since the train is moving 50 MPH with respect to the ground. The train and ball interact at 80 MPH. The ball rebounds from the front of the train at nearly the same 80 MPH, which can be added to the 50 MPH speed of the train, because it acquired it from the train. The result approaches a total of 130 MPH. This scenario is analogous the velocity of a spacecraft being added to the velocity of the massive speeding planet, and "rebounding" with a higher velocity still (although the spacecraft's "rebound" is a gravitational, rather than a mechanical, interaction, like in the baseball analogy)."
DL's Link
Caution: Only the passengers should try to track the dropped/thrown ball, the driver should always keep their eyes on the road.
