# Where are we : On level ground or on a ramp - moving in a train?

Let's say we are traveling in a train. The path has two parts: one at ground-level and the other moving up on the ramp. The ramp has an inclination of $\arctan\frac{a}{g}$ with the horizontal, where $a$ is the acceleration of the train on level ground and $g$ is the acceleration due to gravity.

The train does not accelerate on the ramp, but moves with a constant velocity. Can we comment where we are (sitting inside the train of course!) when we have only a pendulum hanging on the roof to observe. (windows are blackened)

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generally, on this site "homework-type" questions are tagged as homework even if they don't arise from actual homework assignments. But I'm not the expert on this, I was just trying to be helpful. – Nathaniel Mar 19 '13 at 4:56
@zhermes What i do with Equivalence-principle? – ABC Mar 19 '13 at 6:10
Hi exploringnet. If you haven't already done so, please take a minute to read the definition of when to use the homework tag, and the Phys.SE policy for homework-like problems. – Qmechanic Mar 19 '13 at 8:20

Although the gravitational/inertial force causing the pendulum to tilt in the same way in both cases (see Equivalence principle link of @zhermes) thus not allowing you to see whether you are on accelerating or on the slope, you will probably be able to feel the difference.

The reason is that although the force parallel to the train is equal (which causes the pendulum to behave in the same way), the normal force acting on you is not so depending on the value of $\arctan\left(\frac{a}{g}\right)$ (whether it is sufficiently larger than 0) you will probably be able to feel whether you are on the incline or not.