Transcript 2012 Physics Fall Semester Exam Study Guide: Additional Practice

2012 Physics Fall
Semester Exam Study
Guide:
Additional Practice
Is it ok to bring bookbags, etc. into
the lab area?
NO! This will clutter the lab area.
Why did Newton think the moon
was accelerating?
He knew the moon was moving in a circle, and
objects moving in a circle must have
unbalanced forces accelerating them.
(Otherwise they'd move in a straight line).
What are two key clues you are
studying projectile motion?
1. The object's path of motion is curved.
2. Velocity over time can be determined.
If you break anything made of glass
in the lab, what's the BEST thing to
do?
IMMEDIATELY NOTIFY THE TEACHER!!!
WARN OTHERS OF THE DANGER.
DON'T CLEAN UP YOURSELF!
What is meant by
"terminal velocity"?
This is where speed (velocity) is constant b/c
the force of gravity=the force of air resistance
(so there are no unbalanced forces!)
Of all of today's sources of energy, which
do you think would most likely result in
frequent fluctuations?
Wind. Why? Because wind currents are
variable throughout the day!
What is the NET FORCE acting on an object where
there is a downward (south) force of 5 N and an upward
(North) force of 10 N?
If forces are opposite: SUBTRACT
If forces are same direction: ADD
So... 10N - 5N= 5N Northward Net force
Mechanical Energy=KE or PE
PE=mgh (mass * gravity * height)
KE=1/2mv2 (m=mass v=velocity)
So...If an object has a velocity of 5 m/s and a mechanical
energy of 20J, what's its mass?
***Pick the right equation, based on what you know!
KE=1/2 mv2 Solve for "m".
20J=.5m(5m/s2)
20J=.5m(25)
0.8J=.5m
m=1.6kg
If an object is moving at constant
speed in a circle, what is the
direction of force?
TANGENT to the circle!
Why can't a ball bounce higher than
the point it was released?
The law of conservation of energy says so!
PE gets converted to KE, but no extra energy
can be created, so ball can't go higher than
the height contributing to the original PE!
What is the ACCELERATION of any
object when it is moving
UPWARD/DOWNWARD?
If an object is moving upward, it is only battling
the force of gravity, so the acceleration is the
opposite of gravity, or -9.8m/s2.
Likewise, if an object is moving downward, it's
only accelerated by gravity, so the
acceleration is 9.8m/s2.
How many forces can be shown on
an FBD (free body diagram)?
Forces can act in MANY different directions
(NOT JUST 4!)
So...forces shown on a FBD should represent
as many forces as are present!
Force of gravity between two
objects
Force of gravity is DIRECTLY
PROPORTIONAL to mass of objects &
inversely proportional to distance between.
Equation: F=G x (m1m2/d2)
So if mass of one object triples and mass of the
other doubles, simply multiply 3X2=6 to figure
out how much the force of gravity increases.
Acceleration is DIRECTLY
PROPORTIONAL to change in
unbalanced forces!
So...If forces double, acceleration doubles!
Ex: 5N of force increases to 10N, so
acceleration doubles to 2x's initial
acceleration.
If forces are cut in 1/2, acceleration is too!
Ex: 10N of force decreases to 5N, so
acceleration is 1/2 of what you started with...
Normal Force is AKA Support
Force
So, in a FBD, the normal force is the one in the
UPWARD direction (and so is the support
force b/c they are the same thing!)
Ex:
MOMENTUM=
Mass x Velocity (m x v)
So...If an object has a mass of 10kg and moves
at a rate of 5 m/s for 20 s, what is the
momentum?
Focus only on what you need for the formula!
M=m x v
M=10kg x 5 m/s=50 kg * m/s
Relative Velocity
TRAVELING
VELOCITY
RELATIVE DIRECTION
SAME WAY
add
If going slower than
you, direction is opp
way you are going; If
other object is going
faster, direction=same
way you are travelling
OPP WAYS
subtract
Always = same
direction as other
object
Newton's 1st Law: Inertia
Objects in motion, tend to stay in that same path of
motion; objects at rest tend to stay at rest (unless
outside forces act on them).
Ex: If you make a sharp turn in a moving car,
things will tend to slide in the direction you
were originally going.
Ex: If something is still, it won't spontaneously
start moving unless a force is directed upon
it.
Can anything move faster than the
speed of light???
NO!
This is a violation of the laws of physics!!!
What safety mechanisms are
installed in vehicles to protect
people in crashes?
Seat belts and air bags
How can we tell work has been
done?
The motion of an object changes.
If no change in motion, no work has
been done!
Where can one best observe the
BEHAVIOR of matter?
In deep space, far from any star!
Potential Energy vs Kinetic Energy
PE=Energy stored (at rest) that gets converted
to KE=Energy of motion.
So, if you do work on something, you are
transferring stored (PE) energy into energy of
movement (KE).