Microchip Implant Would you do this?

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: Velocityc

f = .56 Hz

Review: Accelerationc

ac (m/s2) = v2

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?

ac (m/s2) = v2

r

Forcec

• 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

ac = 10.95 m/s2

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 Fc=mac= mv2/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/s2. What is the centripetal force of the rotating bolo?

Fc (N) = mac

Fc (N) = mac = mv2

r

Fc = 2.74 N

Torque NotesUnit Eight

Rotational Mechanics

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 1st 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 N•m. 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?