600!

This is the 600th Index of Refraction blog post - cool...

B and F Blocks began their work with rotational dynamics with a study of torque. Remember that torque is not a force - it is the ability of a force to produce rotation. We looked at some examples of how lever arm affects what the force accomplishes when applied to a rotating body. And don't forget angle - only the component of the force that is perpendicular to the rotation contributes to torque and the formula:

τ = Fd(sinΘ)

takes those factors into account. We looked at a sample problem where three forces acted on a beam and calculated the torque produced by each force. Forces applied directly on the axis of rotation do not contribute to torque and force that do contribute to torque could produce clockwise (-) or counterclockwise (+) rotation. When calculating τ_net, pay close attention to those signs. On Monday, C Block will work on a lab that centers on torque and rotational equilibrium and F Block will move on to take a look at center of mass and moment of inertia.

Which was what B Block discussed today. An object's center of mass is the point on an extended object where it will naturally rotate around when acted on only by gravity. Toss a baseball bat in the air and it will rotate around its center of mass, but the center of mass itself will trace out the characteristic parabolic trajectory of an object demonstrating projectile motion. However, an object can rotate around any point if you apply a torque and some axes are easier to rotate around than others. That leads to the idea of moment of inertia - the resistance of an object to rotation. If the mass of an object is clustered around the rotational axis, the moment of inertia will be lower than if the mass is spread at a distance from the axis. We looked at a couple of demonstrations to see how mass distribution affects rotation, specifically angular acceleration, and we'll pursue that relationship mathematically in a later section. On Monday, we'll move into the arena of the second condition for equilibrium and see how to analyze objects in translational and rotational equilibrium.

E Block continued their lab work on rotational dynamics. All groups have their data now and will work on data analysis on Monday.

Have a good weekend!