1. Pigs
   Horses
2. Herd dogs
   Cows

Horses remained prevalent farm animals until the 1940s, as they couldn't fully be replaced before that. The reason they lasted for nearly 35 years after tractors came about was that farmers couldn't afford tractors during the Great Depression, but WWII changed that.

1. Interior soiler
   Depth soiler
2. Subsoiler
   Trisoiler

Typically using a single blade with a sharpened tip, subsoilers can penetrate tough soil, piercing the ground to depths of around 12 inches. This process can be used to help with drainage problems, as it loosens the soil so the water can drain.

1. Forklift
   Backhoe
2. Grinder
   Scraper

Backhoes are used to pull dirt toward the back of a tractor, which is where its name comes from. The arm of the backhoe consists of two parts: the boom that's attached to the tractor and the dipper that holds the bucket.

1. Corn
   Tomatoes
2. Potatoes
   Bell peppers

Since potatoes grow in the ground, the crop has to be trimmed down to make harvesting the potatoes easier. A haulm topper serves this purpose by trimming the crop without removing the potatoes from the ground.

1. Horizontal to the back
   Horizontal to the front
2. Horizontal to the side
   Vertical to the sky

There are many benefits of having an exhaust pipe run vertically from the tractor toward the sky. One of the biggest benefits is that the exhaust fumes won't damage the crops below as the tractor runs over them.

1. Drill
   Pollinate
2. Sow
   Spade

When it comes to sowing seeds, it's important to know how deep the seeds can be planted to grow appropriately. Seeds planted too far into the ground won't muster enough energy to ever pierce through the soil.

1. Helps with traction
   Keeps the tractor from moving
2. Locks all tires from spinning
   Locks the tires on one side of the tractor

The differential lock causes both of the tires on each side of the tractor to operate as one unit instead of separately, which means they spin at the same speed. This means a tire won't continuously spin in the mud while the other tire doesn't move, providing better traction.

1. 1907
   1918
2. 1946
   1959

When John Deere purchased the Waterloo Engine Company in 1918, the Waterloo Boy became their first major tractor to hit the market. Thousands of these tractors were sold to farmers between 1918 and 1924, at which time John Deere came out with the Model D.

1. Outer cage
   Tip-over bar
2. Roll-over protection structure
   Internal framing

Tractors are the leading cause of death on farms, with most of those deaths being due to overturns. However, a rollover protection structure used in unison with a seat belt can prevent deaths 99 percent of the time.

1. To push
   To power
2. To load
   To drag

Though tractor comes from "trahere," the immediate predecessor to the word was "traction engine." However, the use of tractor to mean "an engine or vehicle for pulling" dates to the very end of the 19th century.

1. They use spark plugs.
   They can be stored without being used.
2. They have more power than gas engines.
   They don't have distributor caps.

Spark plugs are critical for gas engines because they are part of the ignition system, which gets the engine to start. Since a diesel engine doesn't require the same level of heat to fire up, they use glow plugs as part of the ignition system.

1. Reliability
   Endurance
2. Power
   Handling

Because speed isn't necessarily important on a farm, tractors are built to achieve their purpose of dragging equipment along. To accomplish this, a tractor engine is built with less horsepower so that it can maintain its pull power even as the RPMs drop.

1. Raises the front end
   Lowers the back end
2. Shifts gears
   Starts the tractor

The clutch on a tractor is used much like the clutch on a manual car, as both help the vehicle shift gears. However, unlike a car, a tractor can start in a high gear, like fourth gear, without having to shift through the other gears first.

1. Reel mower
   Flail mower
2. Drum mower
   Rotary mower

A reel mower attachment cuts grass in a scissoring motion using anywhere between three and seven blades. It's the most common type of mowing equipment used to cut the grass at golf courses, where an even cut is required.

1. Coal
   Water
2. Gas
   Timber

The steam tractor, which used coal as its power source, was inspired by the steam engine that powered trains and boats. These engines were used in tractors until the 1920s, when combustion engines became prevalent.

1. Apparatuses
   Devices
2. Implements
   Utensils

Implements originally pulled by horses did not directly translate when the first tractors started coming out. Though some farmers tried to attach implements meant for animals, it often resulted in injuries or mechanical problems because tractors wouldn't stop when a problem arose, like if the implement caught a tree stump.

1. Anchor
   Drawbar
2. Coupler
   Hook

Tractors are not the only type of hauling vehicle that utilizes drawbars. These couplings are used to attach loads to a variety of transport equipment including trains and roadway vehicles.

1. Rear receiver hitch
   Gooseneck hitch
2. Pintle hitch
   Three-point hitch

Using three points of attachment, the three-point hitch helps disperse the weight of farm equipment on the drive wheels of a tractor. Distributing this weight provides the tractor with more traction as it moves along.

1. Compression
   Hydraulics
2. Pumps
   Belts

Though not all hydraulic systems are exactly the same, there are a few components they must all have in common. Those components are a container for the fluids, a pump, a valve and a cylinder, all of which work together to make the hydraulics operate.

1. Power lever
   Power rim
2. Power takeoff
   Power rotor

The power takeoff became popular in North America in the 1930s, which had a huge benefit on agriculture. The stubs that are operated by the power takeoff, however, are extremely dangerous and have been a major cause of farm injuries.

1. Universal joint
   Hinge joint
2. Pivot joint
   Pin joint

The universal joint has been around for over 2,000 years, where it was once used by ancient Chinese civilizations. The earliest versions of the joint used interlocking rings to allow candles to remain upright while in motion.

1. Weak
   Strong
2. Low
   High

Torque is important for the movement of a tractor, as it relates to the amount of force a tractor can generate. However, the torque also benefits the attachments on a tractor because it determines how much rotational power a tractor can exert.

1. Pick up hay
   Attach equipment to the front
2. Move around material
   Cut grass

Front end loaders on a tractor can be very dangerous because they change the weight of the tractor, affecting its center of gravity. To help combat this, tractor operators can keep the bucket low to the ground while moving so that the bucket will hit the ground if the tractor starts to tip over.

1. Smaller in the front
   Larger in the front
2. All the same size
   The same size with more grip in the front

Tractors wheels are larger in the back and smaller in the front for two main reasons. First, this helps to keep the front of the tractor from rising up since the axle is higher off the ground. Second, the engine is at the front of the tractor, so larger tires in the back help balance out the weight.

1. Steel
   Wood
2. Aluminum
   Rubber

Prior to the implementation of rubber tires, tractors primarily used steel tires, which caused great discomfort for the operators. The 1930s saw a change to rubber tires, as testing throughout the decade proved that rubber tires were far superior to their steel predecessors.

1. Automobile companies
   Farm equipment producers
2. Railroad companies
   Steamboat companies

Around 75 percent of the tractor market in the United States was controlled by Ford in 1923. Only five years later, though, competition had grown so fierce that Ford was out of the tractor business.

1. John Deere
   Mahindra
2. Kubota
   New Holland

After teaming with International Harvester in 1962, Mahindra started developing tractors for its market in India, where the company was founded. The company wouldn't enter the American market until 1994, but has since come to dominate its competition because of the tractor's reliability on tough terrains.

1. Swather
   Baler
2. Yard scraper
   Cultivator

A cultivator can be used both before planting and after planting. Before planting a crop, the cultivator helps stir the soil to make planting easier. After a crop is planted, a cultivator can destroy weeds that may damage a crop.

1. Water
   Manure
2. Beans
   Compost

Manure helps fertilize the soil for planting crops but can be both labor-intensive and unpleasant to spread. To make this process easier, muck spreaders were invented with the capability of both breaking up the manure and spreading it evenly across the ground.

1. Rotary mower
   Reel mower
2. Flail mower
   Sickle mower

A sickle mower attachment is best for mowing down tall grass or thick vegetation. This type of mower has this benefit because the cut vegetation won't get tangled up in a series of spinning blades like in other mowing equipment.

1. Bale toter
   Bale transport
2. Bale haul
   Bale lifter

Bales of hay are rolled into a round shape to prevent contact with the ground to keep the bale from rotting. These round bales, which are too large to be carried by hand, are hauled around using a bale lifter on a tractor.

1. 1
   2
2. 3
   4

When a tractor is pulling a load, the load is taken off the front tires, resulting in a lack of steering control. To combat this, tractors come with two brakes, which allows a tractor to make a much tighter turn.

1. Miniature tractor
   Compact utility tractor
2. Sports tractor
   Economic purposed tractor

Compact utility tractors have a 540 RPM PTO and are capable of using many of the implements that a larger tractor can. However, these tractors usually weigh less than 4,000 pounds, and their attachment output is less than 40 PTO.

1. Row-crop tractor
   Overhead tractor
2. Spaced-crop tractor
   Vertical tractor

Tires on row-crop tractors are designed where they can appropriately space themselves out so they don't run over a crop but instead run in the rows between crops. Though the term is not often used today, row-crop tractors can be traced back to the 1920s.

1. Two-wheel drive
   Four-wheel drive
2. Pedrail wheel
   Track

Track systems can benefit a tractor user who wants to spread the contact pressure of the tractor across the ground. However, spreading this contact pressure depends on the psi of an inflated tire, as tires with less than 20 psi are actually better for the ground than a track system.