Transcript Centripetal Force

Microchip Implant
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
Fc (N) = mac = mv2
r
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 = 2.74 N
Torque Notes
Unit 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.
Torque
• 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.
Force Causing torque
Fulcrum
Torque
Torque  = Fr
• 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 - 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?