Presentation on theme: "Microchip Implant Would you do this?. Review: Period (T), units - second T (seconds) = Time # of Rotations Little Bobby Bolo noticed his bolo swung around."— Presentation transcript:
Review: Period (T), units - second T (seconds) = Time # of Rotations Little Bobby Bolo noticed his bolo swung around his head 2 times every 3.40 seconds. What period is the rotating bolo? T, (seconds) = Time # of Rotations
Review: Frequency ( f ), unit - Hertz f, (Hz) = # of Rotations Time Little Bobby Bolo noticed his bolo swung around his head 2 times every 3.40 seconds. What frequency is of the rotating bolo? f, (Hz) = # of Rotations Time T = 1.7 s
Review: Acceleration c a c (m/s 2 ) = v 2 r Little Bobby Bolo noticed his bolo swung around his head with a velocity of 2.96 m/s. With a radius of.8 meters What is the centripetal acceleration of the rotating bolo? a c (m/s 2 ) = v 2 r
Force c Centripetal force is a force that PULLS an object towards the center of rotation. Many things can cause centripetal force A string attached to a tetherball The gravity of the Earth and the moon causing the moon to orbit the earth. Friction on the tires of a car as it drives around a circular track a c = 10.95 m/s 2
Centripetal Force An object moving in a circular motion is constantly accelerating. In order to accelerate it must have a net force acting upon it. Remember that F= ma Therefore F c =ma c = mv 2 /r What happens if Fc is eliminated?
Centripetal Force Little Bobby Bolo noticed his.25 kg bolo swung around his head with an acceleration of 10.95 m/s 2. What is the centripetal force of the rotating bolo? F c (N) = ma c F c (N) = ma c = mv 2 r F c = 2.74 N
Rotational Inertia Newton’s law of inertia states… Also applies to rotational motion, call this rotational inertia!!! An object in rotation will continue to rotate unless another force acts on the object. Spinning Top
Torque A force exerted at a distance from the axis of rotation To get an object to move (or) stop in a straight-line, a “force” must be applied. Newton’s 1 st law Thus, to get an object to start spinning, or to alter the rotation of a spinning object, a torque must be applied.
The easiest way to think of torque is to consider a door. When you open a door, where do you push? If you exert a force at the hinge, the door will not move If exert a force on the side of the door opposite the hinge, and to push or pull with a force perpendicular to the door. Torque
Note that the symbol for torque is the Greek letter tau. Torque is the product of the distance from the point of rotation to where the force is applied multiplied by the force Torque has units of Newton·meters Torque Torque (N-m) = Fr
Torque - Example You use a wrench to loosen a bolt. It finally turns when you apply 250 N of force perpendicular to the wrench at a distance 0.3 m from the bolt. Calculate the torque. Force = 250 N Radius (distance from where force is applied) = 0.3 m Torque (N-m) = Fr
Torque - Example The drain plug on a car’s engine is required to be tighten to a torque of 25 Nm. If you are using a 0.15 meter long wrench to tighten the plug, what is the minimum force you need to apply to loosen the plug?
Torque - Example A metal bar is used to pry a rock out of the ground by pivoting the bar under the rock and pushing down the on the other end. The end is pushed with a force of 200 N. If 2.2 m of the metal bar is extended out from under the rock, how much torque is being applied to the crowbar?
Question…. You are using the wrench below loosen bolts on your car tires. At what point would it be easier to loosen the bolt and why?