Simple Machines study guide KEY

advertisement
Name:________________________________________
Simple Machines Study Guide
Force and Work-
1.) To be considered work, you have to have a ______force___ and a ___distance____ through
which the force acts.
2.) What is the formula for work?__work = force x distance_ What is the unit for work?__joules_
3.) What does something have to do to be considered a machine?
A machine is any device that makes doing work easier.
4.) Decide if work is done for each of the following: (Are the requirements for WORK met?)
a. Someone is sitting on a cushion on the floor.
Work or
NO work
b. A baseball is hit into the bleachers.
Work
or
NO work
c. Ms. Jarrett holds a doorstop in one place to show you an example of a wedge.
Work
or
NO work
d. A little girl is pushed on a swing.
Work
or
NO work
Simple Machines Basics
1.) What are the 2 basic types of simple of machines, of which all other simple machines are
variations of? Also list the other simple machines in the correct category under the heading.
___inclined planes_____ & ________levers_____
Wedge
pulley
Screw
wheel and axle
2.) In general, what do most simple machines do?
Simple machines make work easier by reducing the force needed.
3.) Do simple machines make less work? Explain.
No. Simple machines make work easier, they do not decrease the amount of
work. Simple machines can actually make more work due to friction.
4.) What do we mean when we say “machines make work easier?” (force vs. distance)
Simple machines make work easier to do by decreasing the force required by increasing
the distance over which the work is done.
5.) A force applied by a machine to an object is the?
a.) resistance force
b.) effort force
c.) force field
6.) A force applied to a machine by a person is the?
a.) resistance force
b.) effort force
c.) force field
d.) Jedi force
d.) Jedi force
7.) Simple machines make work easier, however there are 2 exceptions to this rule. What are
the exceptions, and in each case, what is the “advantage” each machine gives us?
1. single fixed pulley – changes the direction of a force
2. 3rd class lever – gives us increased speed
Inclined Plane
1.) An inclined plane decreases the ___force____ needed to lift an object by
_____increasing___ the distance that force is applied.
2.) In general, less force = __more__ distance, and more force = __less____ distance
3.) If the force required to lift a barrel into the back of a truck was 124 Newtons without a simple
machine, what would the force required to get the barrel into the back of the truck using a
ramp? (Think in general, you don’t have enough info to calculate.)
a.) less than 124 Newtons
b.) more than 124 Newtons
c.) 124 Newtons
4.) Inclined planes can increase the amount of work done due to ________friction____.
5.) If it takes 45343 joules of work to lift a barrel into the back of a truck without using a simple
machine, how much work would be required to get the barrel into the back of the truck using a
ramp? (Think in general again, and CONSIDER FRICTION)
a.) less than 45343 Joules
b.) more than 45343 Joules
c.) 45343 Joules
If we consider friction, we can conclude that the work would be slightly more due to the friction.
Lever
1.) A lever turns on a fixed point, called the __fulcrum_____.
2.) Other than multiplying a force, what else can levers do?
Change the direction of a force
3.) Explain how you would determine what class a lever is. (Look where and be what?)
Look in the middle and be FRE --- fulcrum in middle = class one, resistance in middle=2,
effort in the middle = class 3
4.) What happens to the force needed to move an object as you
increase the length of effort arm?
force needed would DECREASE as you increase the effort arm
5.) What would happen to the force required if you decreased the length of the effort arm?
If you decreased the effort arm, the force needed would increase
6.) True or False and explain- ALL LEVERS make work easier.
FALSE. The third class lever does
NOT make work easier. They give
you increased speed.
7.) Label the effort, resistance and fulcrum
in the pictures below an identify what class
of lever it is.
Pulley
1.) Pulleys can ___multiply____ a force or change is __________direction____.
2.) What are the three types of pulleys?
Single movable, single fixed, block and tackle
3.) How do you find the mechanical advantage of a block and tackle?
Count the sections of rope supporting the weight
4.) True or False and explain-ALL PULLEYS make work easier.
FALSE. Fixed pulleys do not make work easier, they only change the
direction of the force.
5.) How does the distance of the string you pull compare to the distance the weight is lifted
when using a block and tackle system?
The distance of the string you pull is much greater than the distance the
object is lifted. (Trading increased distance for decreased force.)
6.) What is the MA of a single fixed pulley? ___1_______ single movable pulley? _____2______
7.) Find the effort force required to lift the 300 N weight in
the diagram.
1- 300 N
2- 100 N
Simple vs. Compound Machines
(mentioned in “machines” reading)
1.) What makes something a compound machine instead of a simple machine?
Composed of 2 or more simple machines
2.) Label each machine with “S” for simple and “C” for compound.
a. scissors __C__
d. pry bar __S____
b. ramp __S_____
e. bicycle __C____
c. single fixed pulley ____S___
f. shovel ___S____
3.) List 3 of your own examples of compound machines. (Remember: Machines help make
WORK easier.
Bull dozer, wheelbarrow, nail clippers, etc
Mechanical Advantage Basics
1.) Mechanical advantage is how much the machine ___multiplies__ your force.
2.) What does it mean about a machine if it has a mechanical advantage of 1?
The machines doesn’t increased your effort/ input force. The force the machine applies to
an object is the same as the force you put in. It doesn’t “help” you by making you
stronger.
3.) Would Machines with higher mechanical advantage would take more or less effort force to
make something move?
A.) more
b.) Less
c.) the same
4.) Would machines with higher mechanical advantage would take more or less work to make
something move?
A.) more (with friction) b.) Less
c.) the same
5.) If you have a choice between a machine with a MA of 4 and a machine with an MA of 6, which
machine would it make more sense to use?
MA of 6 – you would not have to use as much effort force
Wheel and Axle1.) Object with larger radius= __wheel___, object with smaller radius=___axle_____________
2.) What would be easier (take less force) to turn and why:
An axle with a diameter of 10cm using a 100cm wheel
An axle with a diameter of 10cm using a 50cm wheel
Why?- It has a larger effort wheel (large wheel). When you increase the effort distance, you
decrease the effort force needed.
3.) What would require the least amount of work to turn and why:
An axle with a diameter of 10cm using a 100cm wheel
An axle with a diameter of 10cm using a 50cm wheel
Why?-Both amounts of work are the same due to the axles being the same. The 100cm
wheel would just be easier because it travels a greater distance.
4.) Calculate the IMA for the following machines. Show your work.
Rw = 11 cm
Ra = 3 cm
IMA=3.7
Ra = 0.5 m
Rw = 3 m
IMA = 6
dw = 2.4 m
da = 0.8 m
IMA = 3
The Screw1.) Which of the screws to the right (A or B) would require the
greatest amount of force to drive into a piece of wood? Why?
A – There are less threads so there is less distance. There is more
force required for a screw with less distance.
2.) Which of the screws to the right (A or B) would be the easiest to
drive into a piece of wood? Why?
B – There are more threads so there is more distance. Since the
rule is the greater the distance, the less the force, there is LESS
force required for the screw with more threads.
3.) Which of the above screws (A or B) would have the greatest mechanical advantage?
B – more threads, more distance, less force
4.) What is a specific advantage we discussed of using a screw instead of an inclined plane?
(Think staircases) completing the same goal using a smaller space
The Wedge
1.) What does the wedge do as it moves into a material?
Separates the material
2.) Of the two wedges to the right, which do you think would require the
least amount of force if you wanted to separate those objects 8cm and
why?
B- it has a greater distance (length) and the rule is when you increase the
distance, you decrease the force (make work easier)
4.) What is a major difference between the wedge and an inclined plane?
The wedge moves
3.) Measure and calculate the IMA of the wedges.
Height = 1.8 cm
Height = 2.6 cm
Slope = 3 cm
Slope = 2.4 cm
IMA = 3 cm/1.8 cm = 1.7
IMA = 2.4cm/2.6 cm = .92
Calculations: Show your work!
Work = force x distance
You will be given the following on your test:
FR
Length of slope
IMA wedge = -------------------------Height or thickness
DE
__________________
_______________
MA x FE
MA = Resistance Force
Effort Force
Radius wheel
IMA x DR
I.M.A = Effort Distance
Resistance Distance
IMA wheel and axle = ------------------------Radius axle
1.) A clown is trying to lift a refrigerator full of wigs a height
of 2M. It would take him a force of 60 Newtons to lift the
fridge without a simple machine.
a.) Exactly How much work would be required to lift this
fridge of wigs without a machine?
Force= 60 N
Distance= 2 M
Work = Force x Distance
W= 60 Newtons x 2 M
Work= 120 Joules
b.) Assuming no friction, how much work would be required to lift the fridge of wigs with a
lever that has a mechanical advantage of 6?
120 joules – the amount of work would not change by using the machine, the work would
just be easier
c.) Assuming no friction, how much effort force would be required to lift the fridge of wigs with a
lever that has a mechanical advantage of 6?
60 N / 6  Force = 10 N
2.) What is the force needed to lift a magic school bus if you use a lever with a mechanical
advantage 25. The force required to lift the magic school bus without a lever would be 1000 N.
M.A = Resistance
effort
or
effort= resistance
M.A
Resistance= 1000 N
Effort= ?
M.A = 25
25 = 1000N
Effort
or
Effort=1000N
25
M.A = 40
3.) How much work is being done by a penguin pushing a purple piano with a force of 50 N up a
ramp that is 8 meters long?
Force= 50 N
Work = Force x Distance
W= 50 Newtons x 8 M
Work= 400 Joules
Distance= 8 M
4.) What is the mechanical advantage if a unicorn uses its horn as a lever to open a door 2 feet
wide using 300 N of force, which would normally take about 900N to open without a simple
machine?
M.A = Resistance
effort
Resistance= 900 N
Effort= 300 N
M.A = ?
M.A = 900 N
300 N
M.A = 3
5.)How much work is required to lift a bag of cat litter 2 meters, if the bag has a force of 40N?
Force= 40
Distance= 2 M
Work = Force x Distance
W= 40 Newtons x 2 M
Work= 80 Joules
6.) Melvin the mighty monkey is trying to get a big bag of bananas into his tree house. It takes
90 Newtons of force to lift into a tree without using a simple machine. He then makes the work
easier by putting a ramp that is 10 feet long up to his tree house, which allows him to move the
bag of bananas with 10 Newtons of force. What is the Mechanical Advantage of this inclined
plane?
Resistance= 90 N
Effort= 10 N
M.A = ?
M.A = Resistance
effort
M.A = 90 N
10 N
M.A = 9
7.) What is the Ideal Mechanical Advantage of a lever whose effort arm measures 55cm and
whose resistance arm measures 5 cm?
Resistance= 5 cm
I.M.A= Effort Arm
I.M.A = 55 cm
I.M.A = 11
Effort= 55 cm
Resistance Arm
5 cm
I.M.A Lever = ?
8.) What is the Ideal Mechanical Advantage of an inclined plane that has a length of 400cm and a
height of 50cm?
Resistance= 50 cm
Effort= 400c m
I.M.A Lever = ?
I.M.A= Effort dist(Length)
Resistance dist(Height)
I.M.A = 400 cm
50 cm
I.M.A = 8
9.) What is the ideal mechanical advantage for a lever whose fulcrum is at 20cm?
Resistance= 20cm I.M.A= Effort Arm
I.M.A = 80cm
Effort= 80cm
Resistance Arm
20 cm
I.M.A Lever = ?
I.M.A = 4
Download
Related flashcards
Create Flashcards