2. Review Quiz 4B
Answer the following in your lab notebook:
1. Name the six types of simple machines.
A: inclined plane, wedge, lever, pulley, wheel & axle, screw
1. What do simple machines do?
A: machines make work easier
1. In science, what is work?
A: work = force x distance
OR: using a force to move an object some distance
1. What is a force AND with what unit is it measured?
A: a push or pull, measured in Newtons
1. What is the mechanical advantage of a first class lever in
which the fulcrum is 20 cm from the load (resistance force) and
80 cm from the effort (applied force)?
MA = 80 cm ¸ 20 cm Mechanical Advantage = 4
Bonus: Name one real-world example of each class of lever.
3. • First Class Lever:
• First Class Lever:
– Fulcrum in middle, load & force on
opposite ends
– Load & force move in opposite
directions.
– Fulcrum in middle, load & force on opposite ends
– Load & force move in opposite directions.
• Second Class Lever
– Load is in middle, with effort on end.
– Load & force move in same direction.
• Third Class Lever
– Bar is attached to fulcrum on one end.
– Load is on end, with effort in middle.
– Load & force move in same direction.
6. Calculating Mechanical Advantage
• MA = (Fulcrum to Effort) ¸ (Fulcrum to Load)
MA = F to Effort distance
F to Load distance
• MA = Resistance Force
Effort Force
(fulcrum to single penny)
(fulcrum to stack of pennies)
(weight of stacked pennies)
(weight of single penny)
7. Wheel & Axle
Wheel and axle: a circular disc (wheel) locked to a
center post (axle).
• One full rotation of the wheel results in one turn of the axle.
• The effort force moves in the same direction as the load.
•When force is applied to the wheel:
– Force is magnified (on the axle)
– The larger the wheel, the less
force needed to turn the axle.
• When force is applied to the axle:
– Force is NOT magnified, but the advantage is
in the increased speed that the wheels turn
8. Wheel & Axle
• To calculate the Mechanical Advantage of a wheel & axle:
MA = wheel diameter ÷ axle diameter
10. Pulley
• Pulley: a grooved wheel with a rope around it,
usually attached to a fixed piece (the "block").
– The larger the wheel, the less force will be needed to
move the load.
• Pulleys can change the direction and/or amount of
force needed to move the load.
– Load & force move in opposite or same
directions, depending on how pulley is
attached.
As the rope is
pulled down, the
flag goes up.
11. Pulley Systems
• When used in combination, pulleys increase
the mechanical advantage.
– To calculate the M.A., count the # of pulleys
– The M.A. also represents the amount of extra
rope needed to pull the object
Single Pulley
MA = 1
Pull the rope 1 ft down to lift the
load 1 ft up
Two Pulleys, MA = 2
½ the force is needed, but twice as much rope
must be pulled (pull rope 2ft down to lift 1 ft up)
13. Inclined Plane
• Inclined plane: any flat, slanted surface that helps
move objects up off the ground.
– A ramp is the most common type of inclined plane.
• higher at one end than the other
• the longer the ramp, the less force is needed to do the work
• force is spread over a longer distance, making it easier to lift
– Inclined planes help by pushing up against gravity's pull on
the load.
• The load (resistance) moves in the same direction as the effort
force.
14. Inclined Plane
• Mechanical Advantage of Inclined Plane:
MA = slope (length or hypotenuse) ÷ height
16. Wedge
• Wedge: similar to inclined plane, but force is applied
differently
– used to push up on or pry apart heavy objects
– can also stop an object from moving (doorstop)
• Effort force is applied to the wide end (usually down)
• Narrow point transfers the force outward to push at
perpendicular angles on the load.
– The load moves in a different direction
than the effort force.
In this picture, as the force moves the ax
down, the load (wood) breaks apart
and falls to the sides.
17. Wedge
• Mechanical Advantage of a wedge is same as
inclined plane:
MA = slope (length) ÷ height (thickness)
10 cm ÷ 2.5 cm
MA = 4
19. Screw
• Screw: an inclined plane wrapped around a center
post
– Distance between threads is called pitch
• Pitch is the distance the screw will advance each rotation
– longer inclined plane (smaller pitch, more/closer
threads) requires less force to move the load
(over longer distance)
• As the effort force rotates the screw, it goes down into
the wood (force changes from rotational to downward)
– Threads of screw increase surface
area friction which allows screws
to hold objects together better
than nails
– Wedge-shaped post allows screw
to go in wood easier
20. Screw
Mechanical Advantage = circumference ÷ pitch
Use the circumference of where the
effort force is being applied.
–Circumference of screw head
OR
–Circumference of screwdriver
handle
Another way of looking at it:
MA = Effort (force) distance
Resistance (force) distance
First class levers: pop can, screw driver on lid, seesaw, catapult, pump handle
Second Class: wheelbarrow, bottle cap, nut cracker
Third Class: fishing pole, snow shovel, ice tongs/tweezers, chopsticks
Knowing what you do about fractions, what happens to a number when the denominator gets smaller? (the number value increases)
Use circumference of where the force is being applied.
Archimede's water screw
How is our current government and culture affecting scientific progress?
