3rd-Nine-Week-Benchmark-SG-Answers

8/7/2019 3rd-Nine-Week-Benchmark-SG-Answers

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3rd Nine Week BenchmarkStudy Guide


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1.

Speed is the rate at which an object movesor how fast it is changing position. The

unit of speed is distance/time like m/s ormph.

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.

A school bus driver begins his route at 6:30a.m. with an odometer reading of 67,930 miles.He finishes his morning run at 9:30 a.m. and hisodometer then reads 68,005 miles. What is theaverage speed of the school bus?

Rememberaverage speed = total distance

total time

Average speed = 68005 67930 = 75 miles = 25 mph

3 hrs 3 hrs


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3.

A unit rate is a how fast something changesin a unit of time (say 1 second or 1 hour).The denominator becomes 1 (a unit) whenyou divide.

Speed = distance / time

Velocity = distance / time in a given direction

Acceleration = final velocity initial velocity time


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4.

Speed only tells how fast something is

changing position

Velocity tells both how fast something is

changing position and in which directionthe object is moving


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5.

Scientists often deal with objects that are

changing direction (so velocity isneeded) or several objects moving inrelation to each other (so direction orvelocity is needed). Stating DIRECTION

in addition to SPEED completes themotion picture!


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6.

time time

distance

distance

Speeddecreasing;

slope is flatter

No changein distanceso speed is

zero

Speedincreasing;steeperslope

Constantspeed; slope

is the same


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7.

Acceleration shows how fast an objectsspeed is changing.

An object can accelerate by:1.Speeding up

2.Slowing down

3.Changing direction4.Speeding up and changing direction

5.Slowing down and changing direction


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8.

Acceleration = final velocity initial velocity timeA car pulls off of I-85 South to an exit ramp

slowing to a speed of 40 mph from a speedof 70 mph. It takes the car 1minute to slowdown. 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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9.

Because acceleration can be defined as achange in speed AND/OR direction, anobject moving at a constant speed is

defined as accelerating if it is changingdirection.

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.

Velocity tells you how fast an object ismoving and the direction in which it is

moving.

Acceleration tells how fast an objects

velocity is changing speeding up,slowing down and/or changingdirections.


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11.

The blades of this

windmill areconstantly changingdirection as they turnat a constant speed.

This centripetal forceis an example ofacceleration.


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12.

You must have more than one force to havebalanced or unbalanced forces.

Balanced forces combine for a net force of zero

and result in no change in motion when appliedto an object at rest or no change in motionwhen applied to an object moving at a constantspeed and in a straight line. In other words,balanced forces dont cause acceleration.

Unbalanced forces combine for some positive ornegative net force. Unbalanced forces cause achange in motion.


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12a, b.

Balanced forces result in no change in an

objects motion. The net force (after addingforces) is zero.

WHEELS PUSHING ON GROUNDFRICTION OPPOSING MOTION

Net Force = 0 resulting in constant speed (no acceleration)


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12a, b.

Unbalanced forcesresult in a change in an objectsmotion causing the object to accelerate (speed up,slow down or change direction). The net force (afteradding forces) is either positive or negative.

WHEELS PUSHING ON GROUNDFRICTION OPPOSING

MOTION

Net force is positive resulting in positive acceleration car speeds up.

- 50 N + 75 N

Net force = 75 + (- 50) = 25 N


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12c.

Balanced forces have a NET FORCE ofZERO resulting in NO CHANGE in anobjects motion.

Unbalanced forces have a POSITIVE orNEGATIVE NET FORCE resulting in a

CHANGE in an objects motion.


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12d.

An object will move in the direction of thenet

force if the net force is not zero.

Pushing with a force of - 75 NFriction 20

N

Pushing with a force of - 75 N

Net force is 55 NFriction 20

N

Net force is 55 N


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12d.


force if the net force is not zero. He pulls up against the

pull down of gravity. Themagnitude of the forcesis equal to the weight ofthe boxes with an equalforce. The net force iszero, so the boxes do notfall or move up.


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12d.


force if the net force is not zero.+ 40 N

- 10N

The net force is + 30 Nto the right (+ direction).

Because the net forceis not zero, this pair offorces is unbalancedresulting in motion ofthe grocery cart.

+ 40 N- 10N

Net force + 30N


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13.

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

Hes liftingbarbells with a

weight of 5 N!5

5


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14a.

Newtons First Law has to do with inertia which is relatedto

an objects mass.

The more mass or inertia an object has, the harder it is toget it to move OR the harder it is to change its movement.

Also, objects that arent moving or that are moving at aconstant speed and in a straight line will keep doing what

theyre doing unless an unbalanced force causes the motionto change. The baseball has low inertia

(mass) and we can make itmove with minimal force. Itwill just sit here unless anunbalanced force is applied.


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14b.

Newtons Second Law tells us how force, massand acceleration are related.

Basically, if you want something to move, thatsomething has a mass (m). To get it to move, youhave to apply a force (F). The equation F = mawill tell you the rate of acceleration (a).

If the dude wants to makethe ball speed up a lot (highrate of acceleration), he isgoing to have to apply a big

kick (force) to it.


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14c.

Newtons Third Law tells us that forcescome in pairs. When a force acts on anobject, that object exerts an equal andopposite force back on the first object.

Example: When you walk down

the street, you push off of thestreet and the streetpushes back on you.


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15.

Newtons Second Law tells us how force,mass and acceleration are related.

For constant mass: F = ma as F a and as F aFor constant Force: F = ma as m a and as m aFor constant acceleration: F = ma as F m and as F m


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17.

Inertia is basically an objects tendency to resist achange in its current state of motion. Inertia isproportional to mass. You can find an objectsinertia by finding its mass.

A. Garbage truck, dumpster, jet plane, spaceshuttle

B. An object that has high inertia (mass) will behard to move if it is not moving because it

encounters more static friction than an objectwith less inertia (mass). Its hard to make thisobject accelerate (speed up, slow down and/orchange direction) because it has a lot of MASSto move differently.


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18.

Mass is measured with a triple beambalance.

Inertia can be measured directly by findingan objects mass or indirectly bydetermining how much force has to be

applied to make something accelerate.


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19.

Friction is a force that opposes motion.Friction is due to contact of surface andthe force between them.

There are several types: sliding, rolling,fluid (including air resistance) and static

(between two surface that are notmoving).


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20.

Because friction is a FORCE that acts in theopposite direction of an applied force,

friction will SLOW an object that is moving ata constant speed.

Static friction is also responsible for a smallpart of an objects inertia (its tendency toNOT move).


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21.

Friction OPPOSES motion so the frictionforce arrow will be in the opposite directionof motion.

MOTION

friction friction


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22.

You can reduce friction by:

- Minimizing force between objects

- Making surfaces more regular or smooth

- Use wheels or change sliding to rollingfriction

- Use a fluid as a lubricant water, oil,

grease


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23. Gravity is a pulling force exerted byanything that has mass.

24. 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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25. Gravity exists everywhere.

26. Gravity is affected by an objects massand its proximity (closeness) to otherobjects.

Gravity increases as an objectsmass goes up (and goes down as massgoes down).

Gravity increases as objects get

closer together (and decreases as theyget farther apart).


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27.

Remember that the pull of gravity (acceleration)here on Earth is g = 9.8 m/s/s. This is aCONSTANT and does not change (for the mostpart).

To find an objects speed after a certain number ofseconds, multiply 9.8 m/s/s by the number ofseconds. 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 t where g = 9.8 m/s/s and t is the time in seconds


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28.

Satellites are able to remain in an orbitalmotion because of a balance betweengravity pulling on an object (free fall) and

its forward motion at a constant speed.When these are in balance, the satellitemaintains its orbital motion.

This force is called centripetal force.


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29.

Gravity from a less massive object willproduce less acceleration.Gravity from a more massive object will

produce more acceleration.Gravity from objects farther from each otherwill produce less acceleration.

Gravity from objects that are closer togetherwill produce more acceleration.


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30. Gravity exists everywhere.

31. An object can never truly be weightlessbecause gravity, that is everywhere,

gives an object weight due to the forcepulling on its mass.


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32.

Both are properties of matter that isdependent on the amount of matter in anobject.

MASS is how much stuff is in something.

WEIGHT is a measure of how gravity pulls

on somethings mass.


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33.

Tool spring scale

34. MASS will not change. WEIGHTchanges depending on the source ofgravity.


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35a.

Work (scientifically) is done on an objectwhen a force is applied and results in theobject moving in the SAME direction as theapplied force.

Example: When you write with a pencil, youare doing work on the pencil because thepencil moves in the direction in which youpush.


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36.

Work = Force X Distance (in same direction) Newtons X meters = N m = joule

If you push a box with a force of 30 N andthe box moves 4 meters, how much workhave you done on the box?Work = F d = (30 N)(4 m) = 120 joules (j)


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37.Carrying a bag of groceries20 m to the car.

Or

Pushing on a stationary wall


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38. Power is the RATE at which work isbeing done.

39.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.

Because energy cannot be created or destroyed (lawof conservation of energy) using a machine does notenable us to get more energy out than we put in.

A machine only makes the work easier to do bychanging the size of the force required or thedirection 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.

The output force is the force that results from using amachine. The input force is the force put into the machine.

Because the equation for work is W = F x d decreasing theoutput force will increase the distance and increasing theoutput force will decrease the distance.

This is the force/distance trade-off.


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42.

Because machines only make doing the workEASIER, machines do not change the AMOUNT ofwork done.

The goal of machines is to make the forces anddistances change to make the work easier.


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43.

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) andonly the direction changes, the distance willbe the same.


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44.

Refer to your simple and compoundmachines table!!!

The 6 simple machines: inclined plane;wedge; screw; levers (1st , 2nd , and 3rd

class); wheel and axle; pulley


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45.

A compound machine is a machine made oftwo or more simple machines.

A bicycle is a compound machine made ofwheels and axles, pulleys (gears and

chain),levers (the pedals) and screws that holdthings in place.


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46.The mechanical advantage of a machinetells you how many times the machinemultiplies the force.

MA = resistance force effort force

Example: If a machinesinput force is 10 Newtons andthe output force is 50 N, themechanical advantage is:

MA = 50 N = 510 N


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47.Mechanical efficiency is a comparison of the

machines work output with the machines input.

Mechanical efficiency = work output x 100 work input48.Machines generate less work (output) due to the

formation of heat energy.

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