1. Levers
Levers are one of the simple machines that were probably used in prehistoric times. Levers were first described about 260 BC by the ancient Greek mathematician Archimedes ( BC).

2. Levers
A lever is a simple machine that makes work easier for use; it involves moving a load around a pivot using a force. Many of our basic tools use levers, including scissors (2 class 1 levers), pliers (2 class 1 levers), hammer claws (a single class 2 lever), nut crackers (2 class 2 levers), and tongs (2 class 3 levers).

3. Levers
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object.

4. Levers
The lever allows less effort to be expended to move an object a greater distance.

5. The three classes of levers
A first-class lever is a lever in which the fulcrum is located in between the input force and the output force.

6. Class 1 levers Examples: #Seesaw (also known as a teeter-totter)
1. Crowbar or claw hammer (removing nails)
2. Pliers (double lever)

7. The three classes of levers
In a second-class lever the input is located to the far side of the bar, the output is located in the middle of the bar, and the fulcrum is located on the side of the bar opposite to the input.

8. Class 2 Levers # Wheelbarrow # Nutcracker # Door # Pry bar # Stapler
# Diving board

9. The three classes of levers
Class 3 levers. The input effort is higher than the output load. However, also notice that the input effort moves through a shorter distance than the output load.

10. The Lever Lab
To determine how levers change the force required to move an object.

11. Way Cool Levers
The trebuchet is a counterweight siege engine. Basically, a lever and a sling.

12. But First!………...

13. A bit about Siege Engines
Basically there are three ways to power a machine that throws a projectile.
Flexion
Torsion
Levers

14. A bit about Siege Engines
Flexion
Which is the bending of a limb or leaf spring.
Bows, crossbows, and the most ancient of large Greek rock throwing and arrow throwing siege engines were Flexion.
The gastrophetes was the first recorded arrow throwing siege engine showing up around 399 BC.

15. A bit about Siege Engines

16. A bit about Siege Engines

17. A bit about Siege Engines
Torsion
They have arms similar to the limb of a bow on a crossbow, but the arms are independently powered by bundles of semi-flexible sinew cord wrapped into a frame of wood which are pretensioned and then twisted.
Recorded first around 250 BC.

18. A bit about Siege Engines

19. A bit about Siege Engines
The two-armed ballista and catapulta invented by the Greeks and later used by Romans was largely replaced by the Roman onager, which was a much simpler design, using only one arm to propel a rock with a sling.

20. A bit about Siege Engines

21. A bit about Siege Engines
In the early Middle Ages, walls and fortifications had become taller and stronger than they ever were in ancient Greek times, and the stone castle was developed, which had walls stronger than most ancient siege engines could destroy.

22. A bit about Siege Engines
From the Mongolians in the east came the idea for a new type of siege engine, powered by gravity and designed for one purpose; to destroy walls. This was the trebuchet.

23. Trebuchet
The trebuchet is a Type-1 lever and a sling. In the Type-1 lever, the force is applied to one end, the load is on the other end and the fulcrum sits between the two.

24. Trebuchet
The sling is the oldest projectile weapon. There is a pouch to hold the projectile and two long strings. Both ends of the string are held in one hand and the sling is swung around and around. Then, at the proper moment, one end of the sling is let go with the other end is still held by the hand

25. Trebuchet

26. Historic Counterweight Trebuchet Illustrations
Trebuchet from The Romance of Alexander (circa 1330).

27. Historic Counterweight Trebuchet Illustrations
Trebuchet by Kolderer, c1507.

28. Historic Counterweight Trebuchet Illustrations
An early 14th Century trebuchet

29. Historic Counterweight Trebuchet Illustrations
A 13th Century "Mongol" trebuchet

30. Historic Counterweight Trebuchet Illustrations
A fixed-weight trebuchet from the early 16th Century