Inertiometer

General description

In this activity, the falling motion of two objects of different masses is proposed as a tool to study the relativity of reference frames. A first reference frame (K') is put in motion with respect to a second reference frame (K) taken to be fixed. The behavior of the two objects, subjected only to the action of weight force once they start falling, allows the inertial/non-inertial character of the system K' to be revealed.

Instructions

1) Select the value of the acceleration to be assigned to the reference in motion K' (a=0 for an inertial system) 2) On clicking the Start button (which converts to Stop) starts the simulation and the system K' starts moving relative to K. Initially the two objects, the feather and the calibration mass in Vetruvian Man's hands, are fixed in K' and move jointly with it. 3) The two objects can fal freely after a predermined time interval. A free fall in a vacuum is simulated (the acceleration of gravity has been assigned the value 10). 4) The Stop/Start button allows you to stop and restart the fall. 5) To repeat the simulation, click the Stop and Reset buttons in sequence: the initial conditions are restored.

Suggested classroom activities

The simulation lends itself to uses in educational activities devoted to: - the motion of falling bodies in vacuum (it is emphasized that it does not depend on mass) - the relativity of motion in the description in two different inertial reference systems - how to detect whether a reference system is inertial (inertiometer function) - how to detect an acceleration of the reference system (accelerometer function)

By changing the value of the acceleration of the reference frame K', the trajectory of the feather in the reference frame K:

Select all that apply

A
becomes a vertical line
B
remains a parabola, but its concavity changes
C
it is always the same parabola
D
becomes a straight line whose slope depends on the value of

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The simulation shows the falling motions of two objects of very different mass, a feather of mass about 1g and a calibration weight of mass 1kg. In contrast to what we can observe daily, in the K reference system (reference system at rest) two objects arrive at the ground at the same time because:

Select all that apply

A
the simulation is wrong, the heavier object always comes first
B
the simulation is reliable, but only for the special case where the calibration weight is slowed down by air resistance over its greater surface area
C
the simulation is wrong, the feather comes first because it is more aerodynamic than the calibration weight
D
the simulation is valid in the absence of air or for all cases where the effect of air is negligible

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In the reference system K' (system in relative motion), the two objects:

Select all that apply

A
they arrive simultaneously on the ground only when K' is inertial
B
their trajectories are segments with different slopes
C
their trajectories are always parallel
D
the feather comes first if

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Comparing the motion of the feather in the two reference systems, we can say that:

Select all that apply

A
The speed of the feather in K' is less than its speed in K
B
the feather takes the same time to reach the ground in K and in K', but only if K' is accelerated with
C
the feather reaches the ground in K' earlier than in K because it travels a shorter trajectory
D
the acceleration of the feather is always the same in K and in K' regardless of the motion of the latter

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Using the key with the question mark the system K' is given a random acceleration. Knowing that the acceleration of gravity , what value can we take from the simulation to derive the unknown acceleration?

Select all that apply

A
The concavity of the trajectory in K
B
The total displacement of the feather along the x-axis
C
The total displacement of the feather along the y' axis
D
The ratio of the vertical and horizontal displacements of the feather

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Inertiometer

General description

Instructions

Suggested classroom activities

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