# Lesson 1 An Engineering: Introduction to Machines–Levers (December 5 & 6)

Objectives: (1) To introduce students to the basic concepts of machines, as used by engineers; and (2) to specifically learn the principles of levers.

INSTRUCTIONS:

2. Complete the questions in the blue box beneath the article.

#### Simple Machines

from Mr. Tunon’s powerpoint

• When you hear the word “machine”, you probably think of something like a bulldozer or a steam locomotive. But in engineering & science, a machine is anything that makes a force bigger. So a hammer is a machine. A knife and fork are a pair of machines. And even an egg whisk is a machine.
• All these machines have one thing in common: when you apply a force to them, they increase its size and apply a greater force somewhere else.
• You can’t cut meat with your hand alone, but if you push down on a knife, the long handle and the sharpened blade magnify the force you apply with your hand—and the meat slices effortlessly.
• When you pound a nail with a hammer, the handle increases the force you apply. And because the head of the hammer is bigger than the head of the nail, the force you apply is exerted over a smaller area with much greater pressure—and the nail easily enters the wood. Try pushing in a nail with your finger and you’ll appreciate the advantage a hammer gives you.
• There are five main types of simple machine:
1. levers,
2. wheels and axles (which count as one),
3. pulleys,
4. Incline planes, and
5. screws.
###### LEVERS
• A lever is the simplest machine of all: it’s just a long bar that helps you exert a bigger force when you turn it.
• A lever is a rod or bar that turns on a pivot (the fulcrum). The effort applied at one place moves a load at another place via the fulcrum. There are three different types of levers, each with the effort, load, and fulcrum in different places.
• When you sit on a see-saw, you’ve probably figured out that you need to sit further from the balance point (known as the pivot point or fulcrum) if the person at the opposite end is heavier than you.
• The further away from the fulcrum you sit, the more you can multiply the force of your weight. If you sit a long way from the fulcrum, you can even lift a much heavier person sitting at the other end—providing they sit very close to the fulcrum on their side.
• Levers have been used since prehistoric times for cultivation, excavation, and moving large objects. Such implements as hoes, slings, and oars were conceived and constructed to enhance human effort.  As early as 5000 B.C.E., a simple balance scale employing a lever was used to weigh gold and other items.1
• The word, “lever” comes from a French word, meaning “to raise.”2

QUOTE:

“Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.”

— Archimedes3

There are 3 parts to a lever:4

1. The Fulcrum is the fixed support about which the lever moves.
2. The Effort (Force) Arm is the part of the lever to which some kind of force is applied. Its length is equal to the distance from the fulcrum to the point where force is applied.
3. The Load (Resistance) Arm is the part that moves against a weight or other form of resistance. Its length is equal to the distance from the fulcrum to the point where the resistance is concentrated.

There are Three classes of levers:

Levers are all around us. Hammers, axes, tongs, knives, screwdrivers, wrenches, scissors—all these things contain levers. All of them give leverage, but not all of them work the same way.

Class 1: Fulcrum in the middle: the effort is applied on one side of the fulcrum and the resistance (or load) on the other side, for example, a seesaw, a crowbar or a pair of scissors. Mechanical advantage may be greater than, less than, or equal to 1.

• With a long lever, you can exert a lot of leverage. When you use an axe or a wrench, the long handle helps to magnify the force you can apply.
• The longer the handle, the more leverage you get. So a long-handled wrench is always easier to use than a short-handled one. And if you can’t budge a nut or bolt with a short wrench, try one with a longer handle.
• Class 1 levers reduce the force needed to move weights. They do this by increasing the distance through which the force acts.
• For example, a 1-kilogram force acting through a distance of 3 meters can move a 3-kilogram weight 1 meter, if friction is ignored. Speed is lost in a lever of this kind. The weight moves only 1/3 as fast as the force arm.
• Force (F) multiplied by the length of the force arm (Af) is equal to the resistance (R) multiplied by the length of the resistance arm (Ar).
• This can be stated as follows: F *Af = R * Ar
• This formula makes it possible to calculate how much force must be applied to a given lever to move a certain resistance.

Class 2: Resistance (or load) in the middle: the effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow, a nutcracker, a bottle opener or the brake pedal of a car. Load arm is smaller than the effort arm. Mechanical advantage is always greater than 1.  It is also called force multiplier lever.

Class 3: Effort in the middle: the resistance (or load) is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the jaw. The effort arm is smaller than the load arm. Mechanical advantage is always less than 1. It is also called speed multiplier lever.

1. According to the definition in this article, NASA’s InSight lander, which recently landed on Mars, and a pair of scissors are both examples of “machines?” (TRUE OR FALSE)
2. Name the 5 main types of simple machines, according to the article.
3. What are the 3 parts to a lever?
4. Explain how a class 1 lever works.
5. Draw a diagram of a class 1 lever. Label the parts.
6. Give 5 examples of a class 1 lever.
7. Explain how a class 2 lever works.
8. Draw a diagram of a class 2 lever. Label the parts.
9. Give 5 examples of a class 2 lever.
10. Explain how a class 3 lever works.
11. Draw a diagram of a class 3 lever. Label the parts.
12. Give 5 examples of a class 3 lever.
13. Who was Archimedes, and why should we care what he had to say about levers?
14. Consider the quote attributed to Archimedes in this article. Is this quote LITERALLY true? Explain (give logical reasons in support of what you say) why or why not.
15. Assume you have a 12 foot lever, and 100 pound bag of sand. You want to use a class one lever to lift the bag, but you can only exert 20 pounds of force opposite the bag of sand. Explain where you would place the fulcrum and why? Show and explain your calculations. Ignore any affect of friction.
16. A crowbar is an example of which class of levers?
17. If you ignore the effect of gravity, it is impossible to break a lever, no matter how much force is applied? TRUE or FALSE?
18. A common pair of pliers is an example of which class of lever?
19. Chopsticks are an example of which class of levers?
20. Fill in the blank (the same word goes in BOTH blanks): Third class levers are used in applications where ________ is important. Because a larger force is applied by the effort, the load travels a further distance. Since the load travels a further distance, its ________ is also multiplied.
21. SHORT ESSAY (minimum 10 lines):  The article mentions five main types of simple machines.  In your opinion, rank these five simple machines in order of importance to modern human beings. Provide a short explanation after each item as to why you ranked it as you did.
1. SOURCE:  New World Encyclopedia, (http://www.newworldencyclopedia.org/entry/Lever)
2. SOURCE: New World Encyclopedia, (http://www.newworldencyclopedia.org/entry/Lever)
3. Archimedes was a Greek mathematician, philosopher and inventor who wrote important works on geometry, arithmetic and mechanics.
4.   SOURCE:  Ron Kurtis’ School for Champions (https://www.school-for-champions.com)