February 13, 2009
Science/Gravity Question?
I was thinking recently and thought of this:
If you were in a train that was going… say 70 miles per hour. Aboard the train you had one of those mini- rc helicopters. If while the train was in motion, you had the helicopter hover, would the force of the train pulling the helicopter wear off and eventually the helicopter would get left behind since there is no force pulling the helicopter along with the train?
But there is no force to make the "helicopter get left behind". It's in motion at 70mph, the air around it is in motion at 70mph, and it will continue in motion at 70mph.
"force of the train pulling" no such thing!
"force pulling the helicopter along with the train" no such thing!
Remember Newton's law, "A body continues to maintain its state of rest or of uniform motion unless acted upon by an external unbalanced force."
or
objects in motion will continue in motion unless acted on by an external force.
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Filed under Mini RC Helicopter by RC Heli Guy
Comments on Science/Gravity Question? »
But there is no force to make the "helicopter get left behind". It's in motion at 70mph, the air around it is in motion at 70mph, and it will continue in motion at 70mph.
"force of the train pulling" no such thing!
"force pulling the helicopter along with the train" no such thing!
Remember Newton's law, "A body continues to maintain its state of rest or of uniform motion unless acted upon by an external unbalanced force."
or
objects in motion will continue in motion unless acted on by an external force.
.
References :
the helicopter is suspended in air inside the train cabin, and becomes independent of the motion of the train when it takes off from the floor or seat of the train, but dependent on the motion of the air win the train cabin
the train is pulling the air in the cbain along with it, so there is no relative motion of train and air to stop pulling the helicopter along.
now if the air WASN'T moving along with the copter (like if it was on a flatcar instead), the effect would be almost immediate
References :
No, assuming that the train is a closed compartment, the air in the train is moving with the train.
There is no "force of the train pulling the helicopter." Forces don't cause motion; they cause acceleration. If the train is moving at a steady 70 miles per hour, it is not imparting any forces to the people, air, helicopters, etc., within it AT ALL that are any different from those imparted by a train at rest.
References :
Assuming the train is entirely enclosed, your helicopter has a forward motion equal to that of the train. As long as you take off from the floor of the train and remain in the enclosed area, the reference body for your helicopter is always the train itself. They move as a unit.
Even though the ground is moving backwards at the speed of the train, your helicopter, since it's moving in reference to the train, it knows nothing about it.
You can travel all day long this way, and your helicopter will stay hovered at the same location.
By the way, I understand what you mean by "force pulling the helicopter along with the train." You mean the forward momentum. That doesn't change. If you are sitting at the ground looking at this, your train and the helicopter starts out by having the same forward momentum. This momentum is preserved unless different force acts upon it. The momentum does not wear out without specific force acting against it.
References :