Download Introductory Physics: Midyear Review

Introductory Physics: Midyear Exam Review
MOTION
Displacement and Distance
• displacement: straight line distance between 2 points (how far away you are from where
you started
• vector
• distance: measurement of actual path traveled
• scalar
• displacement and distance are measured in meters (m)
Vectors and Scalars
• vector: quantity w/magnitude and direction
• scalar: quantity w/only magnitude
Average Speed
• speed: rate at which distance is covered (how fast something is moving)
• scalar
• measured in meters per second (m/s)
d
s = ----Δt
Average Velocity
• velocity: speed in a given direction
• vector
Δx
v = ----Δt
Δv = vf - vi
• constant velocity: when both the speed and the direction are constant (no acceleration,
must travel in a straight line)
• measured in meters per second (m/s)
Acceleration
• rate of change in velocity (applies to changes in speed or direction)
• vector
• applies to increases and decreases in speed
Δv
vf - vi
a = ----- = ---------Δt
Δt
• distance traveled by an accelerated object:
d = 1/2 a•t²
• measured in meters per second² (m/s²)
Free Fall and Vertical Motion
• free fall: falling in the absence of air resistance (only gravity)
• anything moving in a vertical motion will feel the acceleration of gravity (gravity pulls
on anything moving up and down)
Motion Graphs
• TIP: independent variable (usually time) always goes on the x-axis
Measurement
QUANTITY
Time
Distance
Displacement
Speed
Velocity
Acceleration
Force
Weight
Momentum
Impulse
Energy
Work
Power
VECTOR OR
SCALAR?
VARIABLE USED TO
NAME OF UNIT USED TO MEASURE
ABBREVIATION FOR
REPRESENT IT
IT
UNIT
scalar
scalar
vector
scalar
vector
vector
vector
vector
vector
vector
scalar
vector
vector
t
d
Δx
s
v
a
F
--------------p
Δp
E
W
P
second
meters
meters
meters per second
meters per second
meters per second²
Newton
Newton
s
m
m
m/s
m/s
m/s²
N
N
kg • m/s
N•s
J
J
W
kilogram • meters per second
Newton-second
joule
joule
watt
FORCES
Basic Force Concepts
• force: a push or pull
• vector
Examples:
• gravity
• air resistance
• normal
• tension
• friction
• net force is found by adding up all the forces along a line together
• unbalanced force: when the net force is not zero -> causes change in motion
• TIP: draw free-body diagrams
Newton’s 1st Law: The Law of Inertia
• inertia: reluctance of a body to change its state of motion, mass is a measure of inertia
• The Law of Inertia: An object at rest tends to stay at rest and an object in motion tends
to stay in motion with the same speed and in the same direction unless acted upon by an
unbalanced force.
• Basically that means: changing something’s velocity (speed or direction)
in any way there needs to be an external force acting on it
Newton’s 2nd Law: F = m • a
• The acceleration of an object as produced by a net force is directly proportional to the
magnitude of the net force, in the same direction as the net force, and inversely
proportional to the mass of the object. Force equals mass times acceleration.
• Basically that means: Newton's 1st law tells us that there needs to be a force to
accelerate (change the velocity of) an object. Newton's 2nd law answers the question by
telling us how much force is required.
F=m•a
rd
Newton’s 3 Law: The Law of Action and Reaction
• All forces in the universe occur in equal but oppositely directed pairs. For every action
there is an equal, but opposite reaction.
• Basically that means: Every force has an equal reaction that’s going the other
direction.
Gravity
• g = ~10 m/s²
• distance traveled by a falling object:
d = 1/2 g•t²
Static and Kinetic Friction
• friction: force that acts to resist the relative motion (or attempted motion) of objects or
materials that are in contact
• static friction: the friction that keeps an object that could potentially move from doing
so, but it has a limit (basically: the type of friction you have when something could fall,
but isn't) (example: static friction keeps a book on the edge of a table from fall, but when
too little of the book is touching the tabletop there isn't enough static friction)
• kinetic friction: the friction which exists when two surfaces are contacting and relative
in motion to one another (basically: the type of friction you have when something is
moving) (example: a book sliding down a slope has kinetic friction
Mass vs. Weight
• weight: pull of gravity on an object
• measured in Newtons (N)
• mass: measure of an object’s inertia, measure of amount of matter in an object (how
much stuff something is)
• measured in kilograms (kg)
• TIPS:
• weight changes depending on location, mass doesn’t
• to convert mass into weight multiply by 10 (this is because F=m • a, the
acceleration (a) is gravity which is ~10 m/s²)
Newton’s Law of Universal Gravitation
• Every object attracts every other object with a force that for any two objects is directly
proportional to the mass of each object
• Basically that means: The gravitational force between objects is larger for more
massive objects. The gravitational force is less as objects get farther away.
• Inverse Square Law:
(G = Universal gravitational constant)
F=
m1•m2
G ----------d²
MOMENTUM
Basic Concepts of Momentum
• momentum: inertia in motion
• measured in kilogram • meters per second (kg•m/s)
(momentum’s symbol is p)
p=m•v
Impulse
• impulse: amount of external force applied over a period of time
• impulse is equal to the change in momentum
• measured in Newton-seconds (N•s)
(momentum’s symbol is p)
(impulse’s symbol is I)
I = F • Δt = Δp = m • Δv
Collisions
• elastic collision: when objects collide without being permanently deformed and without
generating heat (when objects collide but don’t stick together)
• inelastic collision: when colliding objects become tangled or couple together (when
objects collide and stick together)
Law of Conservation of Momentum
• In the absence of an external force, the momentum of a system remains unchanged.
• Basically that means: when objects collide, their system (all objects together)
still has the same momentum as before the collision.
net momentumbefore = net momentumafter
ENERGY, WORK, POWER
Work
• measured in joule (J)
F•d=W
Power
• power: rate of work (how fast work is done)
• measured in watts (W)
W
P = ----Δt
Potential Energy
• potential energy (PE): the energy that is stored and held in readiness by virtue of its
position
• gravitational potential energy (GPE): potential energy due to elevated positions
PE = m • g • h
GPE = weight • height
(because weight = m • g)
• measured in joule (J)
Kinetic Energy
• measured in joule (J)
• kinetic energy (KE): energy of motion
KE = ½ m•v²
• Work-Energy Theorem
W = ΔE
Law of Conservation of Energy
• Energy cannot be created or destroyed. It can only be transformed from one form into
another, but the total amount of energy never changes.
• Basically that means: the total amount of mechanical energy (ME) is going to
stay the same from the beginning (before an object has begun its fall) to when it is right
about to hit the ground.
ME = KE + GPE
MEbefore fall = MEduring fall
You know you’re ready for the midyear exam when you…
know the difference between displacement and distance
know the difference between vectors and scalars
know how to solve problems involving distance, displacement, average speed,
average velocity, time and acceleration
know how to create and use motion graphs to relate distance, displacement, average
speed, average velocity, time and acceleration
can figure out if an object is accelerating from descriptions, graphs, or motion maps
can describe the motion of an accelerating object
know the units for the concepts we’ve studied
can describe and use Newton’s First Law
understand that mass is a measure of inertia
can describe and use Newton’s Second Law esp. to solve word problems using forces,
masses, and accelerations
can use a free-body force diagram to show forces acting on a system that has more
than one object
can figure out the net force acting on a system and between two objects based on a
diagram with only co-linear forces (forces going along the same direction)
know the difference between static and kinetic friction and can describe their effects
on the motion of objects
can describe and use Newton’s Third Law
know the difference between mass and weight
can solve problems relating mass, weight, and acceleration (often gravity)
understand Newton’s Law of Universal Gravitation
can define and calculate the kinetic energy of an object
can define and calculate the gravitational potential energy of an object relative to the
ground
can interpret and provide examples that illustrate the law of the conservation of
energy
can use the law of conservation of energy
can describe energy changing between kinetic and gravitational potential energy
know what energy, work and power are
know how to find energy, work and power
know how to calculate momentum
know the law of conservation of momentum, how to use it, and proved examples that
illustrate it
Good luck!