- #1
SophiaSimon
- 15
- 3
Homework Statement
Classical Mechanics: John Taylor[/B]
(1.27) The hallmark of an inertial reference frame is that any object which is subject to a zero net force will travel in a straight line at a constant speed. To illustrate this, consider the following experiment: I am standing on the ground (which we shall take to be an inertial frame) beside a perfectly flat horizontal turntable, rotating with constant angular velocity ω. I lean over and shove a frictionless puck so that it slides across the turntable, straight through the center. The puck is subject to zero net force and, as seen from my inertial frame, travels in a straight line. Describe the puck's path as observed by someone sitting at rest on the turntable. This requires careful thought, but you should be able to get a qualitative picture. For a quantitative picture, it helps to use polar coordinates; see Problem 1.46.
Homework Equations
[/B]
[tex]a_r=\ddot{r}[/tex]
[tex]a_φ=\ddot{φ}[/tex]
[tex]v_r=\dot{r}[/tex]
[tex]v_φ=\dot{φ}[/tex]
The Attempt at a Solution
[/B]
To make this problem as simple as possible (I think), I started the puck at the center of the circle, which I took as the origin, and chose the puck to travel along the [itex]φ=0[/itex] axis with a constant velocity [itex]v_o[/itex] in the [itex]S[/itex] frame. In this frame, the puck will travel along a straight line from [itex](r,φ)=(0,0)[/itex] to [itex](r,φ)=(R,0)[/itex], where [itex]R[/itex] is the radius of the turntable. Therefore, in the [itex]S[/itex] frame,
[tex]a_r=a_φ=0[/tex]
[tex]v_r=v_o[/tex]
[tex]v_φ=0[/tex]
[tex]r=v_ot[/tex]
[tex]φ=0[/tex]
In the [itex]S'[/itex] frame, the puck will start at the origin and travel southeast with a curved trajectory from [itex](r',φ')=(0,0)[/itex] to [itex](r',φ')=(R,φ_{final})[/itex]. In this frame, the puck is seen to have some centripetal acceleration since the direction of its linear velocity changes, but no tangential acceleration since its speed remains constant. Therefore, this frame is non-inertial because the puck has a zero net force on it but is seen to accelerate. In this frame,
[tex]a'_r=-ω^2r'[/tex]
[tex]a'_φ=0[/tex]
[tex]v'_φ=-ω[/tex]
[tex]r'=\cos(-ωt)[/tex]
[tex]φ'=-ωt[/tex]
I am not quite sure if this is correct, and I would like to gain some insight. Please show me any misconceptions I have or incorrect math processes that I have taken.