AP Physics 1: Algebra-Based Flashcards: Rotational Inertia
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 14 cards to help you master important concepts.
In the parallel axis theorem equation, I' = I_cm + Md², what does the term 'd' represent?
The term 'd' represents the perpendicular distance between the axis through the center of mass and the new, parallel axis of rotation.
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In the parallel axis theorem equation, I' = I_cm + Md², what does the term 'd' represent?
The term 'd' represents the perpendicular distance between the axis through the center of mass and the new, parallel axis of rotation.
What two factors determine a system's rotational inertia?
Rotational inertia is determined by the mass of the system and the distribution of that mass relative to the axis of rotation.
What is the equation for the rotational inertia (I) of a single point mass (m) rotating at a perpendicular distance (r) from an axis?
The equation for the rotational inertia of a point mass is I = mr².
Using the parallel axis theorem, if the axis of rotation is moved away from the center of mass, how does the rotational inertia change?
The rotational inertia increases by an amount Md², where M is the total mass and d is the distance the axis was moved.
How does concentrating a system's mass farther from the axis of rotation affect its rotational inertia?
Concentrating mass farther from the axis of rotation increases the system's rotational inertia, making it more resistant to changes in rotation.
What is the formula for the total rotational inertia (I_tot) of a collection of point masses (m_i) at various distances (r_i)?
The total rotational inertia is the sum of each mass times its distance from the axis squared: I_tot = Σ m_i r_i².
Is it easier to rotate a long rod about its center or about one of its ends? Why?
It is easier to rotate the rod about its center because this axis passes through its center of mass, resulting in the minimum rotational inertia.
How is the total rotational inertia of a system of multiple objects calculated?
The total rotational inertia is the sum of the rotational inertias of each individual object about that same axis (I_tot = Σ I_i).
Describe the rotational inertia of a rigid system.
It is a measure of the system's resistance to angular acceleration, which depends on the mass and how it is distributed relative to the axis of rotation.
What is the Parallel Axis Theorem?
The parallel axis theorem (I' = I_cm + Md²) relates the rotational inertia about an axis through the center of mass (I_cm) to the inertia about a parallel axis a distance 'd' away.
What does the parallel axis theorem describe?
It describes the rotational inertia of a rigid system rotating about an axis that is parallel to an axis passing through the system’s center of mass.
What is rotational inertia?
Rotational inertia measures a rigid system’s resistance to changes in its rotational motion.
When is a rigid system’s rotational inertia at its minimum value?
A rigid system’s rotational inertia is at a minimum when the rotational axis passes through the system’s center of mass.
Two objects of equal mass rotate around an axis. If object A is farther from the axis than object B, which has a greater rotational inertia?
Object A has a greater rotational inertia because its mass is distributed farther from the axis of rotation.