Unit 3
Lesson 8
Simple Machines
S8.C.3.1.3
1
Work
No Work being done!
• W=FxD
• Is the force applied through a distance
• Object must move in the same direction as
the force
• Unit for work is a joule (Newton* meter)
Simple machines
• Make work easier by letting us :
1. Apply less force over more distance
2. Change the direction of the force
• They do NOT reduce the amount of work.
•They just make work easier by changing the
size or direction of the force
2
Simple Machines
1. Inclined plane
2. Screw
3. Lever
4. Wheel and Axle
5. Wedge
6. Pulley
3
Inclined Plane
10 N
25 N
•Applying Less force over a greater distance
•Same amount of work is done both ways.
•Ramp makes work easier
•The longer the ramp, the easier the work
becomes because you need less applied force
4
Screw
• A long inclined plane wrapped
around a cylinder
• Like a road that winds around a
mountain
• Less force over a greater distance
5
Wedge
• Wedge change the direction of a force (down with gravity)
• Wedge also allows you to use less force over a
greater distance to split an object apart
• a wedge is really 2 inclined planes back to back
6
Pulley
• Changes the direction of the applied force not the size
of the force applied.
• Makes lifting easier as the person can use their weight
7
to assist in lifting.
Lever
• Changes the direction of
the force
• Apply less force over a
greater distance
•Allows you to move a big
force using a small force
8
Wheel and Axle
•Allows you to apply less force over a
greater distance
• A small force to turn the wheel a large
distance becomes a large force that
turns the axle a small distance
• doorknob is an example
•The screwdriver is a wheel & axle, with the handle as the wheel.
•It's not much wider than the blade, so the force isn't multiplied
much.
•If you had large hands to grip a really wide-handled screwdriver, 9
it would be easier to turn a screw.
Mechanical Advantage
-Using a simple machine gives you
an advantage over not using one
(makes work easier)
20 inches
4 inches
-Indicates how much easier the
work becomes after using a simple
machine
10 N
50 N
-Increasing the mechanical
advantage makes the work easier
because you need less applied
(input force).
MA = 50 N / 10 N
MA = 5
10
Mechanical Advantage
20 inches
4 inches
MA = 20 in / 4 in
10 N
50 N
MA = 5
11
1
A
.
doorknob is a type of wheel and axle.
In the doorknob shown above, when the
handle is rotated a distance of 49
millimeters, the spindle is rotated a
distance of 7 millimeters. What is the
mechanical advantage of this doorknob?
12
50 lb effort force
200 lb load
A wheelbarrow contains a lever.
For the wheelbarrow above, when the
handles are lifted 12 centimeters, the
load is lifted 3 centimeters.
What is the mechanical advantage of
this lever?
13
Hydraulic Lifts
-Have a mechanical advantage
-Force for distance trade-off
Small force is applied to
a piston over a large
distance
Large force is applied to a
piston over a small
distance
14