Projectile

File:155fire.jpg

A projectile being fired from an artillery piece

A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found in warfare and sports (for example, a thrown baseball, kicked football, fired bullet, shot arrow, a ball from a cannon, stone released from catapult).

In ballistics, mathematical equations of motion are used to analyze projectile trajectories through launch, flight, and impact.

Motive force

File:Schwerer Gustav projectile 2.jpg

Projectile and cartridge case for the huge World War II Schwerer Gustav artillery piece. Most projectile weapons use the compression or expansion of gases as their motive force.

Blowguns and pneumatic rifles use compressed gases, while most other guns and cannons utilize expanding gases liberated by sudden chemical reactions by propellants like smokeless powder. Light-gas guns use a combination of these mechanisms.

Railguns utilize electromagnetic fields to provide acceleration along the entire length of the device, greatly increasing the muzzle velocity.

Some projectiles provide propulsion during flight by means of a rocket engine or jet engine. In military terminology, a rocket is unguided, while a missile is guided. Note the two meanings of "rocket" (weapon and engine): an ICBM is a guided missile with a rocket engine.

An explosion, whether or not by a weapon, causes the debris to act as multiple high velocity projectiles. An explosive weapon or device may also be designed to produce many high velocity projectiles by the break-up of its casing; these are correctly termed fragments.

In sports

File:Baseball.jpg

Ball speeds of 105 miles per hour (169 km/h) have been recorded in baseball.

In projectile motion the most important force applied to the projectile mass is the propelling force. In many sports, the propelling forces are provided by muscles that accelerate the projectile (ball, disc, javelin, hammer, dart), and the stronger the propelling force, the faster and farther the projectile will travel. See pitching, bowling.

As a weapon

Delivery projectiles

Many projectiles, e.g. shells, may carry an explosive charge or another chemical or biological substance. Aside from explosive payload, a projectile can be designed to cause special damage, e.g. fire (see also early thermal weapons), or poisoning (see also arrow poison).

Wired projectiles

Some projectiles stay connected by a cable to the launch equipment after launching it:

• for guidance: wire-guided missile (range up to 4,000 metres or 13,000 feet)
• to administer an electric shock, as in the case of a Taser (range up to 10.6 metres or 35 feet); two projectiles are shot simultaneously, each with a cable.
• to make a connection with the target, either to tow it towards the launcher, as with a whaling harpoon, or to draw the launcher to the target, as a grappling hook does.

Equations of motion

An object projected at an angle to the horizontal has both the vertical and horizontal components of velocity. The vertical component of the velocity on the y-axis is given as $V_y=U\sin \theta$ while the horizontal component of the velocity is $V_x=U\cos \theta$. There are various calculations for projectiles at a specific angle $\theta$:

1. Time to reach maximum height. It is symbolized as ($t$), which is the time taken for the projectile to reach the maximum height from the plane of projection. Mathematically, it is given as $t=U\sin \theta /g$ where $g$ = acceleration due to gravity (app 9.81 m/s²), $U$ = initial velocity (m/s) and $\theta$ = angle made by the projectile with the horizontal axis.

2. Time of flight ($T$): this is the total time taken for the projectile to fall back to the same plane from which it was projected. Mathematically it is given as $T=2U\sin \theta /g$.

3. Maximum Height ($H$): this is the maximum height attained by the projectile OR the maximum displacement on the vertical axis (y-axis) covered by the projectile. It is given as $H=U^2{\sin }^2\theta /2g$.

4. Range ($R$): The Range of a projectile is the horizontal distance covered (on the x-axis) by the projectile. Mathematically, $R=U^2\sin 2\theta /g$. The Range is maximum when angle $\theta$ = 45°, i.e. $\sin 2\theta =1$.

See also

• Projectile use by non-human organisms
• Traveling charge

References

• Heidi Knecht (29 June 2013). Projectile Technology. Springer Science & Business Media. ISBN 978-1-4899-1851-2.

External links

• Open Source Physics computer model
• Projectile Motion Applet
• Another projectile Motion Applet