The Physics of World War II

WWIIWeaponry

M1 Garand Rifle•Standard for US infantry soldiers

•Shoulder weapon

•Gas operated

•Weighs 8.94 pounds, is 43 inches long, barrel is 22.30

inches

•Muzzle velocity of 2,760 feet per second, maximum range

of 5,500 yards

M1 Carbine•Also a shoulder weapon

•Gas operated with an effective range up to 200 yards

•Length 36 inches, barrel 18 inches, weight 5 pounds

•Muzzle energy (muzzle velocity x bullet weight) of a .30 caliber M-1 carbine is considerably greater than the current military caliber .223 round

Browning Automatic Rifle•Gas operated, air-cooled

•May be fired from the shoulder or from the hip

•47 inches long, 15.5 pounds, can fire 450 shots per minute

•May be mounted on a bipod

•Can be adjusted to fire semi-automatically, which is much

slower than automatic firing, but more accurate

•Semi automatic firing does not heat the weapon as much

Mortar•Type of cannon used for high angle fire

•The shell is often stabilized in flight by tail fins

•The light shell has a maximum effective range of 3,280 yards; the

heavy has a range of 1,280 yards

Mortar Problem(From a physics textbook posted on hypertextbook.com)

“An artillery shell with an initial velocity of 300 m/s at 55 degrees above the horizontal. It explodes on a mountainside 42.0 s after firing. What are the x and y coordinates of the shell where it explodes relative to its firing point?”

Range is equal to the horizontal velocity multiplied by the time. The time a projectile is in the air is determined from its initial vertical velocity. For example...

vx = vicos = (300 m/s) x (cos 55°) = 172 m/s

vy = visin = (300 m/s) x (sin 55°) = 246 m/s

t = 2·vy/g = (2 x 246 m/s)/(9.8 m/s2) = 50.2 s

x = range = vxt = 172 m/s x 50.2 s = 8640 m

By examining the physics of artillery and using computations like the ones above, experts have been able to make great advances in increasing the ranges of artillery shells overtime. Army troops are now able to stay farther away from the enemy and still manage to cause great damage.

A Closer Look at the Physics of a Firearm

• The goal of a firearm is to deliver maximum destructive energy to the target with minimum delivery of energy and momentum back to the shooter

• But due to the law of conservation of momentum, the impact to the target can be no greater than the impact of the recoil

• However, the smaller size of the bullet, compared to the gun-and-shooter system allows significantly higher energy to be imparted to the bullet than to the shooter, giving guns their lethal effect

(…continued)• Consider a system in which the gun-and-shooter system has a mass of

M and the bullet has a mass of m. The two systems move away from each other with new velocities V and v. Then, by the law of conservation of momentum, MV=mv, and thus V= mv/M and the kinetic energies imparted to the two systems are respectively ½ MV2

and ½ mv2. By doing more calculations we can figure out that the ratio of the energies is the same as the ratio of the masses of the bullet and the shooter. However, almost all of the energy will be dissipated in the target.

• When the bullet strikes, its high velocity and small area mean that it will exert large forces on any object it hit

THE DIFFERENT TYPES OF AIRCRAFTS USED IN WWII AND AN EXPLANATION OF HOW EACH TYPE OF AIRCRAFT WORKS

Key Subjects:

The balance in force of weight and lift and of drag and thrust The flutter phenomenon of an airplane wing

Above a certain speed, power is extracted extremely fast from the surrounding air-stream, with the potential of destroying the airplane. Wing flutter used to be a mystery to the early airplane builders - and pilots, when its phys- -ical origin was not yet understood. Meeting the flutter criteria is still a critical consideration in any airplane design, but in WWII, scientists made sure that every plane had a safe design to minimize casualties.

Fighter Jets

Bombers

Attack Jets

Dive Bombers

Torpedo Bombers Cargo Transport

Liason Airplanes

Trainers

Observation Aircrafts

Helicopters

Bombers, dive bombers, and torpedo bombers were all developed with similar physical characteristics:

Bombs could cover a range over 1500 miles (some went up to 3000 miles)

1000-2000 horsepower leading to balanced thrust

Some of the physical characteristics of the Attack and Fighter Jets include:

In Fighter Jets, only the pilot boards

In Attack Jets, a pilot and a gunner

Average Propulsion: 2000-3000 hp

Physical Characteristics include:

Aboard Cargo/Transport (Top Right), 3 crew members….About 1200 hp

Liason/Observation planes (Bottom Left), 2 crew members….Only 300 hp

Trainers, 2 crew members…similar to Liason Aircrafts

Helicopters (Bottom Right), used for rescuing up to 4 people…About 500 hp

The Atomic Bomb

Nuclear Decay• The minimum amount for a critical mass for U-235 is

52Kg, for Pu-239 it is 10Kg. • Neutron fired into a U-235 atom creating a U-236 atom.• The decay of U-236 into an atom of Ba-141 (barium), an

atom of Kr-92 (krypton) and three neutrons releases a significant amount of energy.

• The three available neutrons collide with other U-235 atoms causing them to fission producing more free neutrons. This process continues creating a chain reaction in the (critical) mass of the U-235 Isotope. The mass can fission quickly as the number of split atoms grows exponentially.

The left side of the equation has a mass of 236.045563 and the right side totals to 233.849298. The difference between the masses (2.196265) must, by Einstein's equivalence principle, appear as energy released in the reaction. This energy is represented as intense heat; 200MeV with each fissioned molecule. 1 MeV (million electron volts) = 1.609 x 10 -13 joules

Though the mass is small, the energy is calculated by multiplying the speed of light squared, than multiplied by the number of atoms that fission during the process!

Bomb Design

Little Boy Considered a gun-type bomb. A disc of uranium 235 is shaped with a center section missing. The center bullet, is place down the barrel from the larger ring mass. A conventional explosive is used to propel the center section into the larger ring section. The two sections then come together forming a critical mass and starting the reaction. The barometric sensor detects the height from the surface of the Earth by measuring air pressure. This allowed the bomb to be exploded above the ground reulting in more damage.

Little Boy was dropped on Hiroshima on August 6, 1945. The explosion, which had the force of more than 15,000 tons of TNT, instantly and completely devastated 10 square km (4 square miles) of the heart of this city of 343,000 inhabitants. Of this number, 66,000 were killed immediately and 69,000 were injured; more than 67 percent of the city's structures were destroyed or damaged.

Fat Man                                                                                                      A Beryllium/Polonium mixture, which is radioactive elements that release neutrons, is placed in the center of a sphere. The sphere is made up of equally spaced and shaped plutonium sections. The sphere looked a lot like a soccer ball. When the bomb was detonated, the sphere implodes, or collapses inward, causing all the plutonium to fuse together thus reaching supercritical mass, and starting the chain reaction. The initial explosion, which caused the implosion, was made by conventional explosive placed evenly on the outside of the sphere.

Fat Man was dropped on Nagasaki on August 9, 1945, producing a blast equal to 21,000 tons of TNT. The terrain and smaller size of Nagasaki reduced destruction of life and property, but 39,000 persons were killed and 25,000 injured; about 40 percent of the city's structures were destroyed or seriously damaged. The Japanese initiated surrender negotiations the next day.

World War II Physics in Video Games

Warning: This could get a little graphic

(That Was a Pun)

The Effects of Gravity on War

Trajectories

The Incredible Falling Bullet

Bombing vs. Dive-bombing

Parachuting, the inevitable result of airplane combat

The Incredible Falling Bullet

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Therefore, if a soldier wanted to hit an enemy in the head from 488 feet away, he would have to aim one foot higher than expected.

Bombing Vs. Dive-bombing

Bombing Vs. Dive-bombingDive Bombing: diving vertically at a target,

releasing the bombs while still in a dive, and only then pulling out into straight flight to get away.

Parachuting: the inevitable result of airplane combat

Parachuting: the inevitable result of airplane combat

Scopes

If you had a "bigger eye," you could collect more light from the object and create a brighter image, and then you could magnify part of that image so it stretches out over more pixels on your retina. Two pieces in a telescope make this possible:

•The objective lens (in refractors) or primary mirror (in reflectors) collects lots of light from a distant object and brings that light, or image, to a point or focus. •An eyepiece lens takes the bright light from the focus of the objective lens or primary mirror and "spreads it out" (magnifies it) to take up a large portion of the retina. This is the same principle that a magnifying glass (lens) uses; it takes a small image on the paper and spreads it out over the retina of your eye so that it looks big.

When you combine the objective lens or primary mirror with the eyepiece, you have a telescope. Again, the basic idea is to collect lots of light to form a bright image inside the telescope, and then use something like a magnifying glass to magnify (enlarge) that bright image so that it takes up a lot of space on your retina

How telescopic lenses Work

                                                            

                                                                                    

Reality Bites