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July 16, 2002
A: FROM MENTOR DANELL OLIVER-COLLINS. TO READ BIO CLICK
HERE.
Physics is the explanation for everything in life. The reason
why you
learned about velocity, acceleration, and speed in a free
fall is to
simplify things by eliminating external factors. The only
way to simplify
it even more is if the experiments were conducted in a vacuum
which can
only be done in space or a special apparatus that has a vacuum
applied to
it. You could look at velocity, acceleration and speed in
everyday life in
automobiles to make it more interesting. To do all the calculations
correctly, as it applies to a car, you would have to consider
friction of
the road, the force of the wind moving against the car, impurities
in the
road which can cause deceleration, deer jumping in front or
the car, etc.
That's a lot to consider when all you really want to learn
is how to
calculate velocity, acceleration, and speed.
When I was working on my physics degree in college I got really
tired of
sliding bricks down an incline plane, working with airplanes
and
automobiles all either in a free fall or vacuum. But simplifying
all
scenarios helped me learn the important parts of the formulas.
Then I was
able to apply what I learned to every situation in life. When
you learn
you need to start simple or it will seem like it is all too
overwhelming.
Don't give up, physics is difficult at first for everyone
just keep things
simple and you will get through it just fine.
July 16, 2002
A: FROM MENTOR MARY JO MULLEN. TO READ BIO CLICK
HERE.
Well, Annie, I'm not sure exactly what you are looking for
but I will give
it a shot and hope that this helps.
Speed is what you think of when you describe movement. It
is a rate of
travel. For example, if you are driving and you go 100 miles
in 1.5 hours,
you were traveling at an average speed of 67 miles per hour
(100/1.5).
Whatever the spedometer in a car measures is instantaneous
speed.
Velocity is for all practical purposes just your speed. The
only difference
between velocity and speed is velocity is a vector. A vector
assigns
direction to whatever it is describing. If you are driving
in a from Los
Angeles to Chicago, your speed is 65 miles per hour, while
your velocity is
65 miles per hour to the east. If you combine a spedometer
with a compass,
you could measure velocity. In physics, you will pretty much
always be
dealing with velocity instead of speed.
Acceleration is the rate of change of velocity. If you take
a car's
velocity at 2 different times and divide by the time between
those
velocities, you get acceleration. A lot of car commercials
brag about their
cars going from 0 to 60 mph in just a few seconds. If a car
went from 0 to
60 in 5 seconds, the acceleration would be 12 mph per second
(60mph-0pmh / 5
seconds) (not a very good example of units, sorry). Similarly,
if you are
standing still and start running, 10 seconds later reaching
a speed of 6
mph, which is also 8.8 feet per second, your acceleration
would be: 8.8
fps/10 seconds or 0.88 feet/second/second. Acceleration is
not something
easily measured, you generally have to calculate it.
Whenever there is a change in velocity, acceleration occurs
(positive or
negative). Acceleration is the basis of Force. Therefore,
whenever you
experience an acceleration, you will feel it. For example,
going back to
the car again, when a stop light turns green and you start
moving, you are
accelerating. If you accelerate slowly you won't feel much
happen. If you
floor it, the high acceleration will push you back into your
seat. Once you
reach your intended velocity and cruise there, you are no
longer
accelerating and will no longer feel like you are being pushed
back.
Gravity is responsible for accelerating objects in free fall.
Gravity is a
constant acceleration of 9.8 meters/second/second or 32.2
feet/second/second. There are many equations (generally referred
to as
Kinematics Equations) that calculate one of the following
components:
velocity, distance, time or acceleration from the others in
the list. Real
life examples of the use of kinematics and physics are numerous.
Any
projectile motion is a great example. A canon firing, a bullet
shot from a
gun, a stunt man jumping a motorcycle over obstacles, throwing
a ball are
all projectile motion. When you throw a ball, gravity eventually
brings it
down to the ground. Gravity is really what determines how
long it will stay
in the air. The velocity with which you threw the ball and
the time that
gravity allows the ball to stay in the air determine how far
the ball will
go. Another example I see often is driving something into
the ground. On a
construction site, piles (long beams) are often driven deep
into the ground
to support buildings in bad soil or hold back earth when you
are digging
deep hole. The machinery which does this is a large weight
that is raised
well above the pile and then dropped on the pile to force
it into the
ground. How hard the pile is hit by the weight is dependent
on gravity and
how high you raise the weight.
Hope I helped and didn't cause any confusion!
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