Shoot!

Choose A or B or C and complete ALL the requirements.

Complete ONE merit badge from the following list. (Choose one that you have not already used toward another Nova award.) After completion, discuss with your counselor how the merit badge you earned uses science and projectiles.

• Archery
• Astronomy
• Aviation
• Digital Technology
• Game Design
• Rifle Shooting
• Robotics
• Shotgun Shooting
• Space Exploration
• Weather

Choose A or B and complete ALL the requirements.

Helpful Links

Be sure you have your parent’s or guardian’s permission before using the Internet. Some of these websites require the use of Java runtime environments. If your computer does not support this program, you may not be able to visit those sites.

Projectile Motion Applets
Website: http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/Projectile/projectile.html

Fowler’s Physics Applets
Website: https://www.compadre.org/introphys/items/detail.cfm?ID=7823

Java Applets on Physics
Website: http://www.cco.caltech.edu/~phys1/java.html

A projectile is:

• An object that is fired, launched, or thrown, but which cannot propel itself
• A self-propelled missile, like a rocket

Projectile motion is the curved path taken by an object that is fired, launched, or thrown.

See www.ncsec.org/cadre2/team1_2/pm.htm.

When an object is fired, launched, or thrown, it is given horizontal velocity. (Velocity is the same as speed, but it is speed in a given direction.) Once the object is launched, no additional force providing horizontal velocity is applied. Newton’s First Law of Motion states that a body at rest stays at rest and a body in motion stays in motion unless acted upon by an outside force. If gravity did not act on the projectile’s path, the object would continue to move in the direction in which it was launched.

Once the object has been launched, the only force acting upon it is the force of gravity, which accelerates the object toward Earth.

Projectile motion is caused by the force of gravity giving vertical acceleration to an object that has horizontal velocity. (When an object is thrown straight up in the air, the force of gravity slows it down, it comes momentarily to a complete stop, then it accelerates downward.) An object that has been launched will continue to move in the direction it was thrown at the speed with which it was thrown, except for being slowed down by friction with the air (air resistance), but it will begin to accelerate toward Earth, moving faster toward Earth all the time. The combination of constant horizontal velocity and increasing downward velocity due to the acceleration of gravity is what gives a projectile its curved path.

Forward velocity is the speed horizontal to Earth given to a projectile. If the projectile is thrown parallel to Earth, all of its original speed will be its forward velocity. If an object is thrown at an angle to Earth, the forward velocity is that portion of the velocity that is parallel to Earth. (Determining forward velocity can be done by separating the velocity into horizontal and vertical components—like on a triangle—using vector resolution.)

Forward velocity has a constant speed.

Acceleration due to gravity slows down things that are moving upward and speeds up things that are moving downward. At most locations on Earth, the acceleration of gravity (9.80 m/s2, or ~32.174 ft/s2) will cause an object to fall 9.8 meters per second faster each second. An object starting with no vertical motion will be falling toward Earth at the rate of 9.8 m/s at the end of one second and at the rate of 19.6 m/s at the end of two seconds. Acceleration due to gravity is constantly changing the vertical speed/velocity of an object.

Escape velocity is the speed at which an object will be able to escape the gravity of Earth, the moon, or other body. An object must travel fast enough that it will not fall back to the surface. Escape velocity from Earth is 11.2 km/s, or 25038.72 mph. Escape velocity is proportional to the square root of the ratio between the mass of the larger body and the distance of the smaller object from the center of the larger body.

Helpful Links

“Escape Velocity”: Georgia State University
Website: http://hyperphysics.phy-astr.gsu.edu/hbase/vesc.html

“Space Environment”: Northwestern University
Website: http://www.qrg.northwestern.edu/projects/vss/docs/spaceenvironment/2-whats-escape-velocity.html

Orbital velocity is achieved when an object’s horizontal velocity balances the acceleration of gravity at that location in space. An object that has orbital velocity (is in orbit) continues to fall toward Earth as it travels away from Earth, giving the object a circular path around Earth. The object continually falls around Earth due to the combination of horizontal velocity and acceleration due to gravity.

Terminal velocity is the point at which the acceleration of gravity on an object matches the air resistance of the object. Terminal velocity is affected by the weight of the object and its orientation. (The more surface area that is horizontal to Earth, the lower the terminal velocity. Skydivers who perform aerial displays use this fact. The first divers to jump lie flat to increase their air resistance. Later divers streamline dive by holding their arms and legs tightly to their bodies and dive headfirst toward Earth in order to catch the earlier divers in the air.)

Note: If it were not for air resistance, all objects, regardless of mass, size, orany other factor, would fall at the SAME velocity.

Watch astronauts David Scott and Jim Irwin do Galileo’s experiment on the moon.
“NASA Lunar Feather Drop Home Page”: NASA
Website: http://er.jsc.nasa.gov/seh/feather.html

When satellites are launched to the east, Earth’s spin effectively adds to their velocity, making escape velocity easier to obtain and requiring less fuel. Not all spacecraft are launched toward the east; the launch direction depends also on the final orbit and purpose of the satellite.

In order for a spacecraft to rendezvous with another spacecraft or other object in space, the orbits of both objects must be taken into consideration. A launch window describes a time period in which a mission must be launched for the objects’ orbits to overlap.

Terminal velocity is when the acceleration due to gravity is matched by the air resistance (or resistance of whatever fluid the object is traveling through). When the acceleration of gravity is balanced by air resistance, the object continues to fall, but it does not increase its velocity.

“A person has a terminal velocity of about 200 mph when balled up and about 125 mph with arms and feet fully extended to catch the wind.” Source: “Speed of a Skydiver (Terminal Velocity),” The Physics Factbook, website http://hypertextbook.com/facts/JianHuang.shtml.

Choose A or B and complete ALL the requirements.

Find out what time a satellite will pass over your area. (A good resource to find the times for satellite passes is the Heavens Above website at www.heavens-above.com.)