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Transcript of Simple Machines
GOAL: I can calculate how much work was done when an object is moved a measured distance.
GOAL: I can observe the effects of friction and examine the variables that increase or decrease it.
GOAL: I can make a lever and investigate the mechanical advantage of it by experimenting with the placement of its parts.
LEVERS & CATAPULTS
GOAL:I can measure the amount of force needed to move an object with and without the help of a wheel.
INVENTING THE WHEEL
GOAL: I can discover the mechanical advantage of a wheel and axle simple machine.
THE WHEEL & AXLE
Compound Machines & Roller Coasters
What are some examples
of work that you know of?
a push or pull on an object
Newton: unit of force
when an object moves as a result of a force acting upon it
Joule: unit of work
W = F x d
a force that
resists motion whenever
the surface of 2 objects
rub against each other.
Rule for friction:
The smoother the surfaces that rub together,
the less friction there will be.
The rougher the surface, the more friction there will be.
a substance that
How is friction important for us in MN?
How many joules of work
will be required to move
75 books from the floor
to a shelf 2 meters high
if each book requires a
force of 2 newtons to lift?
a tool that uses energy to make work easier.
a machine that allows us to do work with less effort.
Wheel & Axle
What are some machines that you are familiar with? How do they get their energy?
What was the load?
What was the arm?
What was the force?
What was the effort?
What effect did moving the
fulcrum closer to or farther from
the load have?
What is the purpose of a catapult?
What are the parts of the catapult?
Load: hex nut
Effort: paper clips
1st class lever
Other than using a lubricant,
how can we reduce the amount
of friction resulting from one
surface passing over another?
Did you need more or less force to move the brick when using the dowels?
Why do you think this happened?
What do we have today that act like dowels and make work easier?
a disk that transfers force to and from an axle around an axis
How might ancient people have invented the wheel as we know it today?
a shaft to which one or more
wheels is attached.
Why do you think it is important that the axles rotate freely in the holes in the frame?
What are you doing as you wind the rubber band?
What is the force that is being applied? Where is the force stored?
The closer the fulcrum is to the load the less effort is needed.
Where did the force to move the wheels forward come from?
Over what distance was the force applied?
W = F x d
The wheel and axle each rotate at the same speed, so they each make a complete rotation at the same time. Therefore, the work they perform is constant.
Does FORCE increase or decrease when it is TRANSFERRED from the axle to the wheel?
Will force increase or decrease when it is transferred from the axle to the wheel?
stays constant and
is changed, what happens to
Will you be performing the same amount
of work in both cases?
Why is this important?
Which is easier?
Which requires less force?
decreases because the circumference of the wheel is bigger than the circumference of the axle. The force needed to turn the wheel 3 rotations is spread out over a greater distance, therefore the force needed is decreased.
Would it be harder or easier to wind the rubber band using a bigger wheel?
DECREASES as it is transferred from an axle to a wheel, so it is INCREASED when transferred from a wheel to an axle. This creates the mechanical advantage!
What household tool uses the mechanical advantage of a wheel and axle?
GOAL: I can examine the structure of a gear and explain its mechanical advantage.
What do you think is
inside this system?
What does this look like?
How is it different from what you have used in previous activities?
a wheel with teeth
How could you rotate this gear without putting the handle into it?
contains the handle and is the gear that transmits force to the other gear
the gear receiving the force
In which direction did the driven gear turn?
How many rotations?
Why do you think the driven gear rotated this many times for every 1 rotation of the driving gear?
the relationship between the number of rotations of each gear
1:3 (driving gear:driven gear)
Why would you add a third gear
in between the driving and driven
Goal: I can construct a simple pulley and measure the force required to lift an object with and without it. I can determine the mechanical advantage of the pulley.
a simple machine made up of a wheel that rotates around a stationary axle.
In which direction was force applied when lifting the book without the pulley?
In which direction did it move?
In which direction was force applied when lifting the book WITH the pulley?
In which direction did it move?
Did you use the same amount of force when you used the pulley as when you did not use it?
How did it help you do work?
A pulley transfers force applied in a downward direction to gain upward lift. REDIRECTS FORCE.
Allows you to raise something higher than you can lift it.
Goal: I can measure the amount of force needed to do a given amount of work, with and without the use of inclined planes. I can discover their mechanical advantage.
How could I move this brick from the tabletop to the top of this stack of books?
Make a hypothesis:
How could you use less force to accomplish the same goal?
A flat surface that is slanted.
The same amount of work was done, but less force was applied over a longer distance.
GOAL: I can observe the use of inclined planes in wedges, use a wedge to perform work, and figure out its mechanical advantage.
How would you describe it?
Did you do work?
How could you tell?
Which was more difficult to drive into the wood?
When you pound a nail into a block of wood, what is the pointed end of the nail causing the wood to do?
The longer the inclined plane, the more distance - and less force - required to move an object. Sound familiar?
How can you connect this to inclined planes?
Think like an engineer:
How would you modify a nail to make it even easier to drive into the wood?
Goal: I can explain how screws make work easier.
Which simple machine does this look like?
What do you think it would look like if it were wrapped around an object?
an inclined plane wrapped around a cylinder
the protruding spirals around the shaft of the screw (really a single, long inclined plane
How do you predict the amount of force required to drive a nail into a scrap of wood will compare with the amount of force required to drive a screw into the wood?
Which did you need less force to drive?
What other simple machines were at work as the screws were driven into the scrap of wood?
Homework: Activity Sheet 12
a machine made up of 2 or more simple machines
Mechanical Advantage - GEAR:
Transfers force from driving
gear to driven gear. This makes