The ballista, or "shield piercer," was first developed by the Greeks using the same principles as a bow and arrow. Its primary use was to, as the name suggests, pierce enemy shields, since normal bows lacked the power to do so. Early versions of the ballista include the gastrophetes, which is nothing more than an enlarged bow that can be braced against the users body.
http://members.lycos.nl/onager/GastrophetesPic.jpg
As time went on ballistas were improved to become larger and more powerful, eventually becoming mounted mechanisms that could be operated by two or more people. The Romans eventually modified them to throw stones, making them more effective in seiges against walled towns.
Ballista Design
http://www.dl.ket.org/latin1/gallery/military/images/ballista_.jpg
The design of the ballista was fairly simplistic. The arms were mounted into twisted ropes, which provided the tension. The ratchet was used to pull the arms back, increasing the tension. A spear or rock was loaded onto the ballista, and the release pin was pulled. The tension on the arms pulled them forward, and the spear or rock was propelled forward by the rope in between the arms.
Ballista Physics
The design of the ballista is such that the force applied from the projectile comes from the tension of the twisted ropes. The ropes, when the tension is released, tend to return to their rest state with minimum tension, much like a spring would expand after being compressed. Using this similarity, the assumption can be made that the forces act in a similar way, and that Hooke's Law can be applied to give at least a general idea of the nature of the force applied by the bal...
... middle of paper ...
...en by the equation
U=mcgh,
where mc is the mass of the counterwieght and g is the acceleration due to gravity. This is converted to kinetic energy of the projectile, given by the equation
K=mpv2/2,
where mp is the mass of the projectile. Once released, the projectile will have a range R given by the equation
R=v2sin2q/g,
where q is the angle from horizontal that the projectile is released at. The maximum range is found at 45°, which makes the range
Rm=v2/g.
Since the potential energy of the counterweight and the kinetic energy of the projectile are the same, the equations can be rearranged to
v2/g=2mch/mp.
Since v2/g is the maximum range,
Rm=2mch/mp.
Bibliography
Serway, Raymond, and Jewett, John. Physics for Scientists and Engineers. Belmont: Brooks/Cole, 2004.
Macaulay, David. The Way Things Work. Boston: Houghton Mifflin Company, 1988
For almost as long as civilizations began they have been fighting against each other. Often times these wars come down to who has the better military equipment. When one army creates an elite war machine another army is sure to soon copy or improve it. For example the U.S. Army Signal Corps purchased the first ever military aircraft in 1902 (Taylor). Two years later the Italians were also using aircrafts. The trebuchet catapult is no exception; it was one of the most destructive military machines of its time (Chevedden, 2000). A trebuchet works by using the energy of a falling counterweight to launch a projectile (Trebuchet). In this research paper I intend to explain the history and dynamics of a trebuchet catapult.
The purpose of the projectile lab is to test the validity of the law of conservation of energy. The application of this law to our everyday lives is a surprisingly complicated process. Conservation of energy states that energy cannot be created or destroyed, but that it can be transferred from one form to another. Consider the projectile lab from document A that this essay is based upon. In an ideal experiment, the projectile is isolated from everything except the gravitational field. In this case, the only force acting on the particle is gravity and there are only two forms of energy that are of interest: the energy of the particle due to its motion (defined as kinetic
First we will examine the primary factors involved with projectile motion in an ideal situation, where no air resistance is involved.
6 What is the maximum effective range of the M203 grenade launcher? Area Target: 350 m; Point Target: 150 m
Crossbows are a highly effective weapon for hunting and war even in today's standards. The first records of crossbows are from China in the 6th century BC. The knowledge then spreads slowly to the west into Europe during the time of the Roman Empire, the greatest empire of all times. The crossbow remained the favored weapon of war and hunting in Rome until the 15th century when gunpowder was also introduced from China.
Before beginning about the history of ball bearing or bullet ball guns, which are referred to as BB guns in short, let’s take a quick peep at some of the most interesting facts about air guns:
Engineers at this time improved the effectiveness of weapons by “extending the throwing arm of the weapon using a rope and a sling” (Rutan). The sling permits the missile to reach a superior velocity by converting kinetic energy.
After the Chinese made the sling like Trebuchet, the lever Trebuchet was made. This version of the Trebuchet was man operated. This machine was also created by the machine and was called the Traction Trebuchet. It fired when a group of men pulled on ropes that were attached to a lever on the machine, which launched the payload. Nevertheless, this man-operated machine, was put through a change again, since the Traction Trebuchet only had a range of 30-61 m and could only throw weights around 110 kg (“Trebuchet”).
So for a 300-grain bullet, the potential energy is calculated by first finding the mass. To do this, take 300grains/7000grains/pound. This gives you a value of .042857lbs. Then we need to convert pounds to slugs (slugs are the units of mass…) .042857lb/32.2ft/s^2=.001331slugs. Now we can calculate the potential energy of our 300-grain bullet. We will assume that h=six feet, since that is roughly the height of the barrel when I shoot from a standing position. So, since PE=mgh, we get PE=(.00133slugs)(32.2ft/sec^2)(6ft)=.256956lbft. The answer is pretty much nothing and so we can pretty much ignore the potential energy of that bullet sitting at six feet in the air, but now lets look at the Kinetic energy of this bullet when shot. Since this bullet will be twisting when it flies, it will have rotational kinetic energy, but I really don’t want to get into those calculations and from what I have read, the amount of energy given by rotation versus that of the charge behind the bullet is really insignificant so I will only calculate the KE as if the bullet is not rotating. The formula is KE=1/2mv^2.
There are many technicalities and terms associated with a successful device. Some of the main factors come from the materials used, and where they were used in the structure. Some are best used in one place, or another. All of this must be taken into consideration when deciding on how to best utilize the physics and forces applied to the boomerang. As it is a simple machine, it dominates in simplicity for a somewhat daunting task.
The ballista was like a much larger version of the crossbow used by besiegers. It got it’s power from being fired with sinew ropes and had two arms. Although the ballista was a great weapon it was hard to construct, therefore the Romans developed a new version called the Mangonel. It, like the Ballista also got it's power from sinew ropes but unlike the ballista which used two arms, the Mangonel only used one arm. To make the Mangonel easier to transport the Romans added wheels. It was very light and could hurl objects such as rocks and even burning projectiles.
There is aspects of physics in almost every aspect of volleyball. Volleyball also follows the three laws of motion provided from Sir Isaac Newton.
The definition of a projectile is an object that the only force acting on it is gravity. Projectile motion is the path the projectile takes. We saw and used this topic a few times in our project. The first time we saw it was when the marble was flew out of the pipe and was in the air. The second time we used the topic to make sure the trains fell on the lever in the correct spot so the golf ball would roll. The third time it was used, was when the board fall on the balloon. It fell as half of a parabola since it started standing up.
Complex technical studies in recent times have shown that one can split a wooden arrow with another, but that it will become stuck in the first shaft, seems nearly impossible. Nowadays, this would be an ‘honor’ more likely for archers who are using tubular shafts made of aluminum or carbon.
In this assessment of the projectile motion of an object, I found that it can be applied to many useful situations in our daily lives. There are many different equations and theorems to apply to an object in motion to either find the path of motion, the displacement, velocity, acceleration, and time of the object in the air.