1. What Classes of Lever Do You See?
Get out Work problem sheet
(we are going to review #4)
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Image:
What Classes of Lever Do You See?

2. Topics in Mechanical Engineering
Unit 3: Engineering Design
Topics in Mechanical Engineering
Simple Machines
Lever, Wheel-and-axle, Pulley, Inclined Plane, Wedge, Screw
Gears and Belts
Cams, Pistons, and Cranks
Other Mechanisms

3. LEVERS Conditions for Static Equilibrium 3 Classes
SF = 0 – Sum of Forces equals 0
SM = 0 – Sum of Moments equals 0
F x dF = L x dL
3 Classes
Mechanical Advantage: the # of times a system multiplies the applied force.
MA = L / F = dF / dL
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.

4. LEVERS
If MA = 4…
What does this tell us about the relationship between L and F?
The system multiplies F by 4, so L is 4x F
What does it tell us about the relationship between dF & dL?
dF is 4x greater than dL. In other words, F needs to travel 4 times as far as L.
Conservation of Energy
Work performed by L must equal Work performed by F
Force Multiplier: pays for it by travelling greater distance
Distance Multiplier: pays for it by requiring greater force
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.

5. INCLINED PLANE Inclined Plane Wedge Screw
Slanted surface used to raise an object
Wedge
Screw
Conservation of Energy: W1 = W2
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright. 1 2

6. PULLEYS Wheel-and-Axle is in the family of levers: MA, F, L, df, dL
Other examples of uses?
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Pulley
Tire on Road
Steering Wheel

7. PULLEYS 1st Class 2nd Class 3rd Class
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images:

8. PULLEYS A pulley is an adaptation of a wheel and axle.
A single pulley simply reverses the direction of a force.
When two or more pulleys are connected together, they permit a heavy load to be lifted with less force.
The trade-off is that the end of the rope must move a greater distance than the load.
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images:

9. PULLEYS MA = L / F M.A. = Total number of strands supporting the load
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
M.A. = Total number of strands supporting the load
MA = L / F

10. PULLEYS
Fixed Pulley – when a pulley is attached or fixed to a strong member, which will not move.
How many strands are supporting the load?
What is the MA of a fixed pulley?
How many lbs of force are required to lift 100 lbs of load?
When a fixed pulley is used, the force needed to lift a weight does not change. 1 1
100
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.

11. Movable Pulley – splits the work in half.
How many strands are supporting the load?
What is the MA of a movable pulley?
How many lbs of force are required to lift 100 lbs of load?
When a movable pulley is used, the force needed to lift a load is half that of the load. 2 2 50
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.

12. PULLEYS
Block and Tackle – a system of two or more pulleys usually used to lift or pull heavy loads.
How many strands are supporting the load?
What is the MA of a movable pulley?
How many lbs of force are required to lift 120 lbs of load?
When a block and tackle is used, the force needed to lift a load is 1/3 that of the load. 3 3 40
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.

13. GEARS & BELTS SPEED Which point on this circle travels fastest?
What is an equation for speed/velocity?
v = d / t
In one rotation, how far has each traveled?
d = C = pD
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright. 1 2 3

14. GEARS & BELTS
FORCE
The Force is multiplied the larger the wheel, for 2nd class system
The distance required to travel is greater, for 2nd class system
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
2nd Class

15. GEARS & BELTS BICYCLE EXAMPLE – Front Sprocket
We have 3 different “gears” attached to the pedal
Where is F applied? Where is resistance L?
In order of greatest MA to least:
1, 2, 3 – why?
MA = L / F = dF / dL
In order of greatest v to least:
3, 2, 1 – why?
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images: 1 2 3

16. GEARS & BELTS BICYCLE EXAMPLE – Rear Sprocket
We have 4 different “gears” attached to the rear sprocket
Where is F applied? Where is resistance L?
In order of greatest MA to least:
4, 3, 2, 1
In order of greatest speed to least:
1, 2, 3, 4
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images: 1 2 3 4

17. GEARS & BELTS BICYCLE EXAMPLE
How does the force required and the speed (distance) alter?
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images: 1 1 2 2 3 4 3

18. GEARS & BELTS BELTS and CHAINS
Connecting two wheels (or gears) of equal or different diameter (circumference).
Rotation is in SAME direction for both
GEARS & BELTS
How gears and belts control movement depends on:
The sizes of the two connecting wheels
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Images:

19. GEAR VIDEO 1 GEARS & BELTS CIRCUMFERENCE
How do you measure the circumference of a circle?
Flexible measuring tape
C = pD
Count teeth
20 – small
30 – large
Gear Ratio
1.5:1, master to slave
GEAR VIDEO 1
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Image:

20. GEAR VIDEO 2 GEARS & BELTS GEAR RATIO
What is the gear ratio of this system?
What does this tell us?
GEAR VIDEO 2
Much of the information in this lesson, and the way in which it is portrayed, comes from David Macaulay’s The New Way Things Work and the Technology textbook by A. Thomas Wright.
Image:

21. Lever Problems
A user is capable of applying 80 lbs. to a 1st-class lever. The mechanical advantage of the user’s current lever setup is 3. What is the maximum load the user is capable of lifting?
A gardener is capable of applying 70 lbs. to lift a wheelbarrow. His hands are placed 4.25 feet from the axle of the wheelbarrow. The weight of the compost that he carries is 2.5 feet from the axle of the wheelbarrow. What is the maximum weight of compost he can carry? What is the mechanical advantage of this setup?
A 3rd-class mechanical lever is used to remove snow without damaging the paved surface beneath it. The machine is capable of applying 600 lbs of force. The distance from the load to the fulcrum is 8 feet. The distance from the applied force to the fulcrum is 4 feet. What is the maximum amount of snow the machine can move at one time? What is the mechanical advantage of the machine?
What is the maximum mechanical advantage of a third-class lever?

22. Pulley Problems
A fixed pulley system is used to lift a bucket from a well. How many pounds of force are required to lift 60 pounds of water?
A movable pulley system is used to accomplish the same task as in #1 above. How many pounds of force are required?
A block-and-tackle pulley system is used to accomplish the same task as in #1 above. How many pounds of force are required?