What Are the Four Rotational Motion Equations Used For?

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SUMMARY

The four rotational motion equations are essential for analyzing the motion of objects in circular paths. They include: 1. \(\theta_2 - \theta_1 = \frac{(w_1 + w_2)(t_2 - t_1)}{2}\) for angular displacement, 2. \(w_2 - w_1 = \alpha(t_2 - t_1)\) for angular acceleration, 3. \(\theta_2 - \theta_1 = w_1(t_2 - t_1) + \frac{1}{2}\alpha(t_2 - t_1)^2\) for displacement with initial angular velocity, 4. \(2\alpha(\theta_2 - \theta_1) = w_2^2 - w_1^2\) for relating angular velocities. These equations are analogous to their linear counterparts, facilitating the transition from linear to rotational dynamics.

PREREQUISITES
  • Understanding of angular displacement, angular velocity, and angular acceleration.
  • Familiarity with basic kinematic equations in linear motion.
  • Knowledge of the relationship between linear and rotational motion.
  • Basic algebra for manipulating equations.
NEXT STEPS
  • Study the derivation and applications of the rotational motion equations in physics.
  • Learn about the concepts of torque and moment of inertia in rotational dynamics.
  • Explore the relationship between linear and angular quantities in detail.
  • Practice solving problems using the rotational motion equations in various scenarios.
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as educators teaching rotational dynamics concepts.

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Homework Statement


My lab book list these four Rotational motion equations and doesn't say what they are. Could someone please tell me what each equation is and what they are used for. thanx


Homework Equations


\theta2-\theta1=(w1+w2)(t2-t1)/2
w2-w1=alpha(t2-t1)
\theta2-\theta1=w1(t2-t1)+1/2alpha(t2-t1)2
2alpha(\theta2-\theta1)=w22-w12

The Attempt at a Solution

 
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The first one isn't correct. The w1 term has different units than the other terms. The second one is analogous to good old ΔV = a*Δt, sometimes written as a = ΔV/Δt. Instead of acceleration, you have rotational acceleration. Instead of velocity, you have rotational or angular velocity.

The third one looks a lot like d = Vi*t + 1/2*a*t², doesn't it?
For the last one, the right side is analogous to Vf² - Vi². Have you seen a formula with that on one side?
 
ok so am i supposed to use one of these to solve my problem? I am just not sure which equation to use
 
hi pb23me! :smile:
pb23me said:
My lab book list these four Rotational motion equations and doesn't say what they are. Could someone please tell me what each equation is and what they are used for …

for an object moving in a circle, the usual linear equations may be used with angular acceleration velocity and displacement instead of ordinary (linear) acceleration velocity and displacement (in other words: with α ω and θ instead of a v and t) …

see the PF Library on https://www.physicsforums.com/library.php?do=view_item&itemid=204" for some details :wink:

(and you use whichever of those equations contains the variables you are given or are seeking)
 
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