3rd Nine Week Benchmark Study Guide

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3rd Nine Week Benchmark Study Guide
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1. Define speed, velocity and distance in your
own words.

• Speed is the rate at which an object moves or how
  fast it is changing position. The unit of speed
  is distance/time like m/s or mph.
• Velocity is both how fast something is moving and
  in what direction.
• Distance is a change in an objects position
  measured in meters in the metric system.

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2. Calculate speed.

• Speed is calculated by dividing distance by time.
• There is average speed which is the speed you
  calculate when speed varies. It is total
  distance / total time.
• There is constant speed which is speed that
  doesnt change. Again, this is calculated by
  dividing distance traveled by the time it took to
  travel that distance.

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Example calculation

• 1. A school bus driver begins his route at 630
  a.m. with an odometer reading of 67,930 miles.
  He finishes his morning run at 930 a.m. and his
  odometer then reads 68,005 miles. What is the
  average speed of the school bus?
• Remember average speed total distance
• total time
• Average speed 68005 67930 75 miles 25 mph
• 3 hrs
  3 hrs

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Example Calculation

• A car is traveling at a constant speed. After it
  has traveled 30 minutes, it has gone a distance
  of 60 km. What is its speed in km/hour?

Speed distance / time Time needs to be in
hours 30 minutes 0.5 hours Speed 60 km / 0.5
hrs 120 km / hr
(about 70 mph)
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3. Explain how speed, velocity and acceleration
are all unit rates

• A unit rate is a how fast something changes
• in a unit of time (say 1 second or 1 hour).
• The denominator becomes 1 (a unit) when
• you divide.
• Speed distance / time
• Velocity distance / time in a given direction
• Acceleration final velocity initial velocity
• time

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4. Explain the difference between velocity and
speed

• Speed only tells how fast something is changing
  position
• Velocity tells both how fast something is
  changing position and in which direction the
  object is moving

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5. Why do scientists find it necessary to have a
different expression for speed and velocity?

• Scientists often deal with objects that are
  changing direction (so velocity is needed) or
  several objects moving in relation to each other
  (so direction or velocity is needed). Stating
  DIRECTION in addition to SPEED completes the
  motion picture!

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Be able to recognize on a graphs changing and
constant speeds (note that these have the same
average speed)
No change in distance so speed is zero
Constant speed slope is the same
distance
distance
Speed increasing steeper slope
Speed decreasing slope is flatter
time
time
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7. Define acceleration and name 5 different ways
that an object can accelerate.

• Acceleration shows how fast an objects speed is
  changing.
• An object can accelerate by
• Speeding up
• Slowing down
• Changing direction
• Speeding up and changing direction
• Slowing down and changing direction

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8. Calculate acceleration

• Acceleration final velocity initial velocity
• time
• A car pulls off of I-85 South to an exit ramp
• slowing to a speed of 40 mph from a speed
• of 70 mph. It takes the car 1minute to slow
• down. What is the rate of acceleration?
• Acceleration 40 70 mph 30 mph
  0.50 mph
• 60 sec
  60 sec sec
• The value is negative because the car is slowing
  down.
• Note units are distance/time/time

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Explain why we must know velocity rather than
speed in order to determine acceleration.

• Because acceleration can be defined as a change
  in speed AND/OR direction, an object moving at a
  constant speed is defined as accelerating if it
  is changing direction.
• For example, a car making a turn
• moving at a constant speed of 25 mph
• is considered to be accelerating.

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10. Explain the differences of acceleration and
velocity.

• Velocity tells you how fast an object is moving
  and the direction in which it is moving.
• Acceleration tells how fast an objects velocity
  is changing speeding up, slowing down and/or
  changing directions.

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11. Explain why an object traveling in a circle
is constantly accelerating even if its
speed/numeric value for velocity is constant.

• The blades of this windmill are constantly
  changing direction as they turn at a constant
  speed. This centripetal force is an example of
  acceleration.

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12. Define and describe the difference between
balanced and unbalanced forces.

• You must have more than one force to have
  balanced or unbalanced forces.
• Balanced forces combine for a net force of zero
  and result in no change in motion when applied to
  an object at rest or no change in motion when
  applied to an object moving at a constant speed
  and in a straight line. In other words, balanced
  forces dont cause acceleration.
• Unbalanced forces combine for some positive or
  negative net force. Unbalanced forces cause a
  change in motion.

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12a, b. Explain and draw force diagrams
including both balanced and unbalanced forces and
how these forces affect motion.

• Balanced forces result in no change in an
• objects motion. The net force (after adding
• forces) is zero.

WHEELS PUSHING ON GROUND
FRICTION OPPOSING MOTION
Net Force 0 resulting in constant speed (no
acceleration)
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12a, b. Explain and draw force diagrams
including both balanced and unbalanced forces and
how these forces affect motion.

• Unbalanced forces result in a change in an
  objects motion causing the object to accelerate
  (speed up, slow down or change direction). The
  net force (after adding forces) is either
  positive or negative.

Net force 75 (- 50) 25 N
75 N
- 50 N
WHEELS PUSHING ON GROUND
FRICTION OPPOSING MOTION
Net force is positive resulting in positive
acceleration ? car speeds up.
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12c. Explain why we need to know a net force to
determine an objects motion.

• Balanced forces have a NET FORCE of ZERO
  resulting in NO CHANGE in an objects motion.
• Unbalanced forces have a POSITIVE or NEGATIVE NET
  FORCE resulting in a CHANGE in an objects motion.

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12d. Be able to identify the direction of motion
based on the net force.

• An object will move in the direction of the net
• force if the net force is not zero.

Net force is 55 N
Pushing with a force of - 75 N
Friction 20 N
Pushing with a force of - 75 N
Net force is 55 N
Friction 20 N
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12d. Be able to identify the direction of motion
based on the net force.

• An object will move in the direction of the net
• force if the net force is not zero.

He pulls up against the pull down of gravity.
The magnitude of the forces is equal to the
weight of the boxes with an equal force. The net
force is zero, so the boxes do not fall or move
up.
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12d. Be able to identify the direction of motion
based on the net force.
An object will move in the direction of the net
force if the net force is not zero.
40 N
40 N
- 10 N
Net force 30 N
The net force is 30 N to the right (
direction). Because the net force is not zero,
this pair of forces is unbalanced resulting in
motion of the grocery cart.
- 10 N
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13. What is the abbreviation for and unit name
for force in the international system of
measurement?

• The unit of measure for force is the Newton,
• abbreviated N.

Hes lifting barbells with a weight of 5 N!
5
5
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14. Newtons Laws Explain each in your own
words

• Newtons First Law has to do with inertia which
  is related to
• an objects mass.
• The more mass or inertia an object has, the
  harder it is to
• get it to move OR the harder it is to change its
  movement.
• Also, objects that arent moving or that are
  moving at a
• constant speed and in a straight line will keep
  doing what
• theyre doing unless an unbalanced force causes
  the motion
• to change.

The baseball has low inertia (mass) and we can
make it move with minimal force. It will just
sit here unless an unbalanced force is applied.
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14. Newtons Laws Explain each in your own
words

• Newtons Second Law tells us how force, mass
• and acceleration are related.
• Basically, if you want something to move, that
• something has a mass (m). To get it to move, you
  
• have to apply a force (F). The equation F ma
• will tell you the rate of acceleration (a).

If the dude wants to make the ball speed up a lot
(high rate of acceleration), he is going to have
to apply a big kick (force) to it.
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14. Newtons Laws Explain each in your own
words

• Newtons Third Law tells us that forces
• come in pairs. When a force acts on an
• object, that object exerts an equal and
• opposite force back on the first object.
• Example When you walk down
• the street, you push off of the
• street and the street
• pushes back on you.

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15. Calculate acceleration given a force and a
mass.

• How fast will a baseball accelerate if it has a
• mass of 0.145 kg and is hit with a force of
• 3400 N?
• F ma solving for a gives us
• a F/m a 3400 N / 0.145 kg
• a 23,400 m/s/s

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16. Understand the relationship between force,
mass and acceleration

• Newtons Second Law tells us how force,
• mass and acceleration are related.
• For constant mass
• F ma as F? a? and as F? a?
• For constant Force
• F ma as m? a? and as m? a?
• For constant acceleration
• F ma as F? m? and as F? m?

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17. Define and explain the properties of inertia

• Inertia is basically an objects tendency to
  resist a change in its current state of motion.
  Inertia is proportional to mass.
• An object that has low inertia (mass) will be
  easy to move if it is not moving.
• An object that has high inertia (mass) will be
  hard to move if it is not moving
• The same is true of changing the objects motion
  if it is moving

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18a and 18b Give examples of objects with
greater inertia and explain why its harder to
make this object accelerate.

• The more mass something has, the more inertia it
  has. Its hard to make this object accelerate
  (speed up, slow down and/or change direction)
  because it has a lot of MASS to move differently.

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19. How do we measure weight and inertia?

• Weight is measured with a scale that shows how
  much gravity is pulling on an object.
• Inertia is measured indirectly by determining how
  much force has to be applied to make something
  accelerate.

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20. Friction

• Friction is a force that opposes motion.
  Friction is due to contact of surface and the
  force between them.
• There are several types sliding, rolling, fluid
  (including air resistance) and static (between
  two surface that are not moving).

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21. Explain what happens in terms of Newtons
Laws to an object with balanced forces when
friction is added.

• Because friction is a FORCE that acts in the
  opposite direction of an applied force, friction
  will SLOW an object that is moving at a constant
  speed.
• Static friction is also responsible for a small
  part of an objects inertia (its tendency to NOT
  move)

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22. Be able to identify the direction of
frictional force in an illustration when the
direction of motion is identified.

• Friction OPPOSES motion so the friction force
  arrow will be in the opposite direction of motion.

MOTION
friction
friction
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23. What are some ways to reduce friction?

• You can reduce friction by
• Minimizing force between objects
• Making surfaces more regular or smooth
• Use wheels or change sliding to rolling friction
• Use a fluid as a lubricant water, oil, grease

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24 and 25. Define gravity and state the Law of
Universal Gravity

• Gravity is a pulling force exerted by anything
  that has mass.
• The Law of Universal Gravity says that
• ALL objects attract each other with a force of
  gravitational attraction. Gravity is universal.

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26 and 27. Where does gravity exist and what
affects it?

• Gravity exists everywhere.
• Gravity is affected by an objects mass and its
  proximity (closeness) to other objects.
• Gravity increases as an objects mass goes up
  (and goes down as mass goes down).
• Gravity increases as objects get closer together
  (and decreases as they get farther apart).

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28. Be able to explain the relationship between
mass and weight.

• MASS is how much stuff is in something.
• WEIGHT is a measure of how gravity pulls on
  somethings mass.
• MASS will not change. WEIGHT changes depending
  on the source of gravity.

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29. Be able to find both the acceleration, speed
and distance an object will reach when dropped.

• Remember that the pull of gravity (acceleration)
• here on Earth is g 9.8 m/s/s. This is a
• CONSTANT and does not change (for the most
• part).
• To find an objects speed after a certain number
  of
• seconds, multiply 9.8 m/s/s by the number of
• seconds. v gt where g 9.8 m/s/s and t
  is time
• To find the distance traveled, use the formula
• h 1/2 g t² where g
  9.8 m/s/s
• and t is the time in seconds

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30. Explain how satellites and orbits work.

• Satellites are able to remain in an orbital
  motion because of a balance between gravity
  pulling on an object (free fall) and its forward
  motion at a constant speed. When these are in
  balance, the satellite maintains its orbital
  motion.
• This force is called centripetal force.

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31. Identify the force of gravity that would
produce the greater or lesser acceleration.

• Gravity from a less massive object will produce
  less acceleration.
• Gravity from a more massive object will produce
  more acceleration.
• Gravity from objects farther from each other will
  produce less acceleration.
• Gravity from objects that are closer together
  will produce more acceleration.

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32 and 33. Why can zero gravity never exist and
why can an object never truly be weightless?

• Gravity exists everywhere.
• An object can never truly be weightless because
  gravity, that is everywhere, gives an object
  weight due to the force pulling on its mass.

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34 and 35.

• What are some tools/instruments used to measure
  mass and/or weight?
• Mass- balance
• Weight- scales
• What is the relationship of mass and weight with
  regards to the force of gravity?
• Mass- stays the same regardless of gravity
• Weight- depends on gravitational force

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36a. Define work and explain how you can
determine if work is done on an object

• Work (scientifically) is done on an object
• when a force is applied and results in the
• object moving in the SAME direction as the
• applied force.
• Example When you write with a pencil, you
• are doing work on the pencil because the
• pencil moves in the direction in which you
• push.

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37. Practice calculating work and know the unit
of measure.

• Work Force X Distance (in same direction)
• Newtons X meters N ? m joule
• If you push a box with a force of 30 N and
• the box moves 4 meters, how much work
• have you done on the box?
• Work F ? d (30 N)(4 m) 120 joules (j)

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38 and 39. Define power and practice calculating
it. What is its unit of measure?

• Power is the RATE at which work is being
• done.
• Power work Example How much power
• time does a machine have that
• can do 500 j of work in 50
• seconds?
• Power 500 j / 50 sec 10 watts

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40. Explain how energy is conserved using a
simple machine.

• Because energy cannot be created or destroyed
  (law
• of conservation of energy) using a machine does
  not
• enable us to get more energy out than we put in.
• A machine only makes the work easier to do by
• changing the size of the force required or the
• direction of the force. If the size of the force
  changes,
• the distance the object moves must change too.
• Remember Work in Work out
• Most of the time it is Work in Work out heat

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41. Explain how changing the output force
affects the distance and the amount of work done.
(see page 195)

• The output force is the force that results from
  using a
• machine. The input force is the force put into
  the machine.
• Because the equation for work is W F x d
  decreasing the
• output force will increase the distance and
  increasing the
• output force will decrease the distance.
• This is the force/distance trade-off.

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41a and b. Explain how work input and work
output are different but related. How do machines
make work easier?

• Because work is constant, the amount of work we
  put
• in is equal to the amount we get out. HOW that
  work
• gets done (force x distance) is how they differ.
• Because machines only make doing the work
• EASIER, machines do not change the AMOUNT of
• work done.
• The goal of machines is to make the forces and
• distances change to make the work easier.

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42. Explain how work changes if the force or
distance is changed.

• Because the equation for work is
• Work Force x distance
• as F ? d ? (work stays
  same)
• as F ? d ? (work stays same)
• If the force stays the same (magnitude) and
• only the direction changes, the distance will
• be the same.

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43. Explain how the six types of simple machines
operate and give an example of each.

• See Section 8.3 for this.
• Make sure you look at the diagrams to
• understand how each works and the
• differences between the three types of
• levers.

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44. Define a compound machine and identify the
simple machines that make up the machine.

• A compound machine is a machine made of
• two or more simple machines.
• A bicycle is a compound machine made of
• wheels and axles, pulleys (gears and chain),
• levers (the pedals) and screws that hold
• things in place.

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What is mechanical advantage?

• The mechanical advantage of a machine
• tells you how many times the machine
• multiplies the force.
• MA output force
• input force

Example If a machines input force is 10
Newtons and the output force is 50 N, the
mechanical advantage is MA 50 N 5
10 N
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What is mechanical efficiency?P. 197

• Mechanical efficiency is a comparison of the
  machines work output with the machines input.
• Mechanical efficiency work output x 100
• work input
• Most machines generate less work (output) due to
  the formation of heat energy. A machine that has
  100 efficiency is called an ideal machine.