Rigid Body Mechanics Lab
IBDP Physics HL • Topic A.4
Understanding the Experiment
In this virtual laboratory, you will investigate the rotational dynamics of a rigid body (a pulley) as a hanging mass causes it to unspool and accelerate. By changing the shape, mass, and radius of the pulley, you can observe how its Moment of Inertia (\(I\)) affects the system's acceleration.
Key Equations (Hover / Tap to flip for definitions)
Newton's 2nd Law
Definition
The net torque on a rigid body is equal to its moment of inertia multiplied by its angular acceleration. (Rotational equivalent of $F=ma$).
Torque
Definition
The measure of the force that can cause an object to rotate about an axis. Depends on force magnitude and the distance from the pivot ($r$).
Linear / Angular Link
Definition
Connects the rotational kinematics of the pulley ($\alpha, \omega$) directly to the linear kinematics ($a, v$) of the falling mass via the radius.
Rotational K.E.
Definition
The kinetic energy possessed by a body solely due to its rotation. A larger $I$ requires more energy to reach the same angular velocity.
Moments of Inertia ($I$)
The resistance to rotational acceleration depends on the mass distribution (shape):
- Solid Disc: \( I = \frac{1}{2}MR^2 \)
- Solid Sphere: \( I = \frac{2}{5}MR^2 \)
- Thin Hoop: \( I = MR^2 \)
The Physics of the Falling Mass
Applying Newton's Second Law to the falling mass (\(m\)):
Applying it to the rotating pulley (\(M\)) with friction (\(\tau_f\)):
Control Panel
Live Telemetry
"Show the Math"
Final Assessment
Test your understanding of Rigid Body Mechanics. These questions require careful calculation. Use your data booklet and scratch paper!