Download Physics Review with Key Ideas #1-19

Use your yellow answer document
Key Idea:
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Average speed = Total distance
Total Time
Total distance = 50 meters
Total Time = 25 min.
50/25 = 2 meters/min.
Check units and make sure
your answer makes sense!
Key Idea: The slope of a distance vs. time
graph tells you the SPEED of the object.
Slope = Rise
Run
Rise = change in distance
Run = Change in time
Distance = Speed
Time
Key Idea: follow the pattern and
predict
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A spring scale
measures force in
Newtons like the ones
we used in class.
The pattern for distance
pulled is every .5 cm =
increase of 2 N
So you can predict:
3 cm = 12 N
And 3.5 cm = 14 N
Key Idea: Speed = Distance
Time
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They gave you speed and time, you do not
know DISTANCE.
So, Distance = Speed X Time
Speed = 9 km/hr.
Time = 30 min. or .5 hours
Distance = 9 km/hr. x .5 hr. = 4.5 kilometers
Make sure your
units make sense!
Key Idea: Must use Speed = Distance
Time
To solve for TIME
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Q: Time = Distance
Speed
Time = 100 meters =
2 m/s
Time = 50 seconds
Check units and
make sure it makes
sense!!!
D
S
T
Key Idea: Velocity is SPEED in a given
DIRECTION
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What is the only answer that includes both
UNITS for SPEED and DIRECTION?
Key Idea: Velocity is SPEED in a given
DIRECTION
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If speed changes, velocity changes
If position changes, velocity can still be constant
If direction changes, velocity changes
If acceleration (change in speed) changes, velocity
changes.
So only B could be correct.
Key Idea: The slope of a distance vs. time
graph tells you the SPEED of an object.
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Slope = Rise
Run
Rise = change in position
(distance)
Run = Change in time
Distance = Speed
Time
Rise = 18 – 0 m___ = 18 m
Run = 10 s – 4 s
6s
Speed = 3 m/s
Key Idea: The slope of a speed vs.
time graph tells you the acceleration
of the object
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First identify what it
is asking.
It is asking how FAR
did it travel.
So it is traveling at
10 m/s for 2
seconds.
D= S X T
D = 10 m/s X 2 sec.
D = 20 m
D
S
T
Use your yellow answer document
Key Idea: Force is described with both direction
(arrows) and magnitude (numbers)
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The forces have the
same magnitude,
but different
directions, so they
are DIFFERENT, so
you can eliminate A
and B.
So D is the only
possible answer.
Key Idea: When forces act in opposite
directions, you find their difference to
calculate net force.
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Difference = 200 N –
150 N
Net force = 50 N
Key Idea: When forces are balanced, an
object does not CHANGE it’s motion.
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Balanced forces cause no CHANGE in motion,
unbalanced forces cause CHANGE in motion.
The forces are BALANCED.
The ball is falling, so we know it will keep falling
due to gravity, but will fall at a CONSTANT speed.
Key Idea: The net force causes an object to
accelerate in the direction of the force.
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Find the Net Force on
the box by finding the
difference between
up/down and left/right
The net forces acts 30 N
DOWN and 10 N to the
LEFT.
So it will move Down
and to the Left
Key Idea: Force = Mass X Acceleration
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This questions wording is
CONFUSING!! It is on
purpose. 
Identify what it is asking:
When would you need to
add MORE force to get
the same
ACCELERATION?
A and B are opposites
C and D would both
speed up the box by
reducing friction
So if you increase mass
you must increase force
Density and Buoyancy
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Density = Mass/Volume
If an object is less dense than the fluid it is in, it
will float, if it is more dense it will sink.
The volume of an object is equal to the volume of
the fluid it displaces.
Buoyant force = the weight of the fluid displaced.
If buoyant force = weight it will float, if buoyant
force is less than the weight, it will sink.
Key Idea: Density = _Mass_
Volume
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Density = 64 g
8 ml
= 8 g/ml
The formula is given
to you on the
reference chart.
USE IT!! 
Key Idea: Objects that are less dense than water
Keythose
Idea:
will float,
more dense than water will sink.
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Calculate the
density of all 4
samples.
Remember the trick
of dividing by base
10: move the
decimal to the left
Which is LESS than
1 g/ml?
#3 will float. The
rest will sink
Key Idea: Objects that are less dense than water
will float, those more dense than water will sink.
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IF it is more dense
than 1.14 g/cm3 it
will sink, if it is less
dense it will float.
Only ironwood is
more dense than
1.14 g/cm3