Physics Midterm Study Guide 2012
Unit 1 – Basics
base units – meters, kilograms, seconds
derived units – combinations of base units, for example, m/s
operational definition of a quantity – definition in terms of the steps used to obtain the quantity
metric prefixes – giga, mega, kilo, deci, milli, micro, nano
measurements
proper measurement – consists of the certain digits and one uncertain (estimated) digit
measurement uncertainty – no measurement is completely true
accuracy – closeness to true value
precision – exactness or fineness of a measurement; how close the scale markings are
significant figures
identifying – Atlantic/Pacific rule
adding and subtracting – smallest number of decimal places controls the answer
multiplying and dividing – smallest number of sig. fig. controls the answer
scientific notation
arithmetic with – know how enter them in your calculator
vector vs. scalar quantities- vector quantities have magnitude and direction, scalars only have magnitude
vector quantities we use are position, displacement, velocity, acceleration and force
identifying relationships in graphs and expressing them as functions
linear y=f(x), quadratic y=f(x2), inverse y=f(1/x), square root y = f(x½ )
dependent and independent variables
Unit 2 – Constant Velocity (CV)
positionx - the distance and direction from the origin
displacementΔx- the distance and direction between two positions Δx = xf - xi
clock reading-t
time interval-Δt Δt = tf - ti
position vs. time graphs (x-t graphs)
the slope of the curve (straight line for CV) represents the velocity of the object
average velocity - v
verbal definition
defining equation v = Δx / Δt
velocity vs. time graphs (v-t graphs)
area under the curve represents displacement
constant velocity
verbal definition – motion characterized by equal displacements in equal times
graphical model is x-t graph and / or v-t graph
mathematical model v = Δx / Δt
motion maps
Adding vectors graphically – put the tail of one on the tip of the other. The resultant vector is the vector from the tail of the first one to the tip of the second one
Unit 3 – Uniform Acceleration (UA)
acceleration – the rate of change of velocity a = Δv / Δt
the acceleration due to gravity on earth (g) is equal to 9.8 m/s2
x-t graph - unless the acceleration is zero (CV) the graph is a parabolic curve
the slope of the tangent to the curve at any point is the instantaneous velocityof the object at that time
v-t graph – the graph is a straight line
the slope of the v-t graph represents the acceleration of the object
mathematical model of UA is the four motion equations. They are derived from the graphical model
vf = vi + aΔt Δx = ½ (vi + vf) Δx = viΔt + ½ aΔt2 vf2 = vi2 + 2a Δx
Unit 4 – Forces, Newton’s 1st and 3rd laws
resolving vectors into x and y components
put the tail of the vector at the origin of an x-y coordinate system
measure the angle from the positive x-axis to the vector. This is called the “standard position”
the vector, the x-component and the y-component form a right triangle
the height of the triangle is the y-component
it is equal to the magnitude of the vector times the sine of the angle
the base of the triangle is the x-component. Use the cosine of the angle to find it
it is equal to the magnitude of the vector times the cosine of the angle
adding vectors
resolve both vectors into their x and y components
add the component to get the components of the resultant vector
use the Pythagorean theorem to get the magnitude of the resultant
use the inverse tangent of the y-component divided by the x-component to get the angle of the resultant
inertia – the tendency of an object to resist change in velocity Inertia a property of mass
particle – a point mass representing the mass of an object.
system – a particle or group of particles whose behavior is of interest We define the system as we wish
surroundings – everything in the environment that is not part of the system
force – an interaction between two objects (or particles)
there are two types of forces
long range forces – pushes or pulls with no physical contact
examples are gravity, electrostatic and magnetic forces
contact forces – direct pushes or pulls due to physical contact
examples are tension, normal force, static friction, kinetic friction and spring forces
the unit of force is the Newton (N). one Newton = one kg-m/s2
normal force (N) – the force exerted on an object by a surface, always in a direction perpendicular to the surface
tension force (T) – the force in a string, rope or cord
net force (ΣF or Fnet) – the vector sum of all the forces acting on an object
The net force can be calculated in the x and y directions separately ΣFx ΣFy
kinetic friction – force between two sliding surfaces, always in direction opposite to the motion
static friction – force between two surfaces that are not moving, always in the direction to resist motion
force diagram
represent the system as a dot
draw as vectors with tails on the dot the forces acting on the system from the surroundings
Newton’s first law – if there is no unbalanced force on an object, its velocity doesn’t change.
so,if an object’s velocity doesn’t change, there is no unbalanced force
also, if an object’s velocity does change, there must be an unbalanced force
According to Newton’s first law, if velocity is constant, ΣF = 0
If velocity is constant in the x-direction then ΣFx = 0
If velocity is constant in the y-direction then ΣFy = 0
Newton’s third law – forces always occur in pairs (sometimes called action/reaction pairs)
the two forces are equal in magnitude, opposite in direction and act on two different objects
to identify the other force in a pair use a verbal pattern like “earth pulls on ball - ball pulls on earth”
Unit 5 – Newton’s 2nd law
ΣF = ma
We use this equation to find m, a, ΣF, or one of the forces included in ΣF
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For the midterm you should be able to
Answer questions regarding any of the definitions and concepts above
Create and analyze x-t and v-t graphs to understand what the object is doing
Use the four motion equations and Newton’s three laws together to solve problems