Work = (Force) (Distance), this simple equation has a few
rules though; the force and distance must not be perpendicular. If this occurs
then no work is done. Even if you apply
force on a wall for instance, and the wall doesn’t move know work is done since
there was no distance component. Work is
calculated in a unit called Jules. 746 Jules equal 1 horsepower. Power is
calculated by dividing work by time. Power is calculated in units named watts.
Work and Kinetic Energy
Change in Kinetic energy is equal to work. In this way
the two are very closely connected. The formula for Kinetic energy is shown
below. Kinetic is moving energy, while potential energy is stored energy.
Simple machines
Simple machines do not change the amount of work to
finish a task. Machines simply lengthen the distance so a lesser force is
needed. Work in equals work out. A ramp which is a simple machine spreads the
distance of lifting an item from 1 meter to 4, so only ¼ the force is needed. Still creating the same amount of
work.
Formulas from the unit
·Work = (Force)(Distance) ·Power = Work / Time · Kinetic Energy = ½ Mass ( velocity^2) ·Potential Energy = Kinetic Energy ·Change in kinetic energy = Work ·Work in = Work out
How is this relevant in
the outside world?
Work and simple machines are found everywhere. Simple
machines create the world around us, and without them there would not be food
on the table, electricity to power our lights, or even lights to be turned on.
Work is everywhere, even whenever we move up and down for instance.
Rotational inertia is how hard or
easy an object is to start or stop turning. An object with a larger rotational
inertia will have more mass farther away from the axis of rotation; this is
seen with the hoop and solid ball experiment. The key to a low rotational
inertia is to have mass evenly distributed, or distributed closer to the axis
of rotation. Angular momentum cannot be destroyed, only transferred. As a
figure skater brings in her hands her rotational inertia lessens, she speeds up
to balance her momentum back to its previous state..
·Torque, and center of gravity
Torque causes rotation. A torque is
created with a force and lever arm, and is inversely proportional. When you
lower your force you must increase you lever arm to counter act the loss to
keep the same torque. Unbalanced torqueses cause rotation. There is always a
clock wise toque, and counter clockwise torque on an object.
-Center of gravity is the area of
average mass, and where gravity pulls down; this is usually half way between
the fulcrum and the edge of an object. When an objects center of gravity moves
outside the base of support the object will fall over. Imagine a person trying
to touch their toes while against a wall. To combat falling over a person will
bend backwards as they lean over keeping their center of mass over their feet
or base. Athletes bend their knees so they are less likely to be rotated off
their base. They also widen their stance so they have a larger base of support
making it harder to be rotated off their base of support.
·Centripetal Force
Centripetal force makes an object
stay in an arc. It is a center seeking force. It makes the object stay tangent
to the axis of rotation. It also ensures that an object keeps moving while
going into a turn. Centripetal force can be found by adding F weight + F
support. Centripetal force is often mixed up with centrifugal force, which does
not exist.
·Rotational and tangential velocity
Rotational velocity is how many
rotations an object completes in a certain amount of time, while tangential
velocity creates a linear distance. A train wheel has tapered wheels, and
though both ends have the same rotational velocity, the larger has more
tangential velocity due to its longer radius. This longer radius is why a car
with over size wheels will go faster than the speedometer reads. An example of
something with the same tangential, but different rotational speeds would be a
gear on a chain. Imagine a bike, the chain running at the same speed but the
larger forward gear runs slower than the smaller rear gear.
What are some things students may have forgotten
while working on this unit?
-Centrifugal force does not exist
·-An object will rotate if its center of
gravity is moved from below its base.
-The farther the average mass is away
from the axis of rotation the more rotational inertia it will have
Rotation
is everywhere, and is the reason earth is habitable. From turning a desk chair,
loosening a bolt, or turning a car this unit can be applied to every situation
even on the sports field. I enjoyed most learning about torque, but was also interested
in rotational inertia. This unit was challenging, but every piece of material can
be directly linked to the real world making it my favorite unit so far.
