CONCEPTUAL PHYSICS Rotational Mechanics

Torque Torques produce rotation. When you exert a turning force, you produce a torque. Ex. When you open a door or when you turn on a water faucet. Torque for an object being turned is the product of the lever arm and the component of the force perpendicular to the lever arm. Torque = force x lever arm Read p 188 T= F x d

Torque and Center of Gravity Balanced torques When balanced torques act on object, there is no rotation. Ex. Seesaw in playground. Counterclockwise torque=clockwise torque Torque and Center of Gravity When the base of support is not under the center of gravity, the gravitational force produces a torque that causes toppling.

Rotational Inertia:The resistance of an object to change its rotational state of motion I = mr2 The greater the rotational inertia, the harder it is to change the rotational speed of an object Ex. Short legs have less rotational inertia than long legs, thus you can run more easily when you bend your knees.

Rotational inertia and gymnastics Objects with their mass concentrated farthest from the axis of rotation have greater rotational inertia. Ex. A hollow cylinder rolls slowlier than a solid cylinder. Objects of the same shape but different sizes will accelerate equally when rolled down an incline. Rotational inertia and gymnastics Read p 195

Angular momentum: the inertia of rotation Rotational velocity: when rotational speed has direction Angular momentum= rotational inertia x rotational velocity M= Iw w: rotational velocity Conservation of angular momentum Law of conservation of angular momentum: if no unbalanced external torques act on a rotating system, the angular momentum of that system is constant. Read p200

1) Calculate the torque produced by a 50 N perpendicular force at the end of a 0.2m long wrench.

CONCEPTUAL PHYSICS Rotational Mechanics