BellringerOf the two types of combined forces, which

one is present if the net force is ≠0.

The Science of Rockets

Notes

A History of Rockets

•A rocket is a device that sends gas in one direction to move the rocket in the opposite direction. A rocket sends gas out the back, causing the rocket to move forward.

A History of Rockets

• In the 1860, the famous science fiction author Jules Verne (Journey to the Center of the Earth; 20,000 Leagues Under the Sea; Around The World In 80 Days) wrote about a 600 foot cannon sending people to the moon.

• Instead of using a cannon, humans eventually used rockets.

•The first rockets were made in China in the 1100s. These rockets were arrows that could be set on fire and then shot with bows.

•The first modern rockets were built in the early 1900s.

A History of Rockets

•Inspired by the works of Jules Verne, around the year 1900, a Russian high school teacher by the name of Konstantin Tsiolkovsky began to describe in scientific terms how rockets work and proposed designs for advanced rockets, but he himself never built one.

A History of Rockets

•Taking it one step farther, around 1915, an American physicist began constructing and testing rocket designs. His name was Robert Goddard.

•Goddard is considered to be the father of modern rocket science.

A History of Rockets

• World War II brought about many advances in rocket technology, primarily by the Germans.

• A German by the name of Wernher von Braun designed the V-2 rocket, which could travel 300 km and was used to destroy many civilian and military targets.

• Towards the end of the war, von Braun and many other German scientists defected to the United States, bringing about 127 of the best German minds to the American’s side.

How Do Rockets Work?

•A rocket moves forward when gases shooting out the back (nozzle) of the rocket push it in the opposite direction.

•Newton’s Third Law of Motion: For every action (gases pushing out of the nozzle) there is an equal and opposite reaction (the rocket is pushed upwards).

How Do Rockets Work?

•A rocket burns fuel inside of a combustion chamber. When the fuel burns, the hot expanding gases are forced out of the nozzle at the bottom of the rocket.

•The force of the gases shooting out of the nozzle is called the action force.

How Do Rockets Work?

•The gases shooting out of the nozzle send the rocket up. The force that moves the rocket forward is called the reaction force.

•The reaction force that sends a rocket forward is called thrust.

How Do Rockets Work?

•For a rocket to leave the ground, the force of the thrust must overcome two other forces that push downward on the rocket, creating a net force >0.

•Weight is the force of gravity on the mass of the rocket.

•Drag is the force of air friction that the rocket encounters as it travels through the atmosphere.

Rocket Velocities

•The greater the thrust, the greater the rocket’s velocity.

•There are three velocities that a rocket can achieve: suborbital, orbital, and escape.

•Suborbital velocity is any velocity high enough to reach 100km above sea level, but not enough to make it circle the planet.

•Suborbital velocity is anything <8km/s.

Rocket Velocities

• In order for an object to orbit, it must reach orbital velocity.

• Anything slower than orbital velocity, and the rocket will fall back to Earth before completing one orbit.

• For Earth’s gravity, orbital velocity is achieved around 7 km/s.

• This is the speed at which artificial satellites and the International Space Station travel.

Rocket Velocities• If a rocket is required to leave Earth’s

gravitational field completely, then it must move even faster. This is known as escape velocity.

• This can be achieved with a velocity exceeding 11km/s or approximately 40,200 kilometers per hour.

• All space probes to other planets and satellites leaving out solar system must travel at this velocity.

Rocket Fuels

•These rapid velocities require special propellants, or fuels. There are three primary varieties:

Solid Fuel (like in fireworks)

Liquid Fuel (like in the space shuttles)

Ion Propulsion (used in modern space probes after leaving orbit)

Multistage Rockets

•A rocket made up of several small rockets is called a multistage rocket.

•In a multistage rocket, smaller rockets are placed one on top of another. Each of the smaller rockets is called a stage. The different stages fire one after the other.

Multistage Rockets

•When a stage runs out of fuel, the stage drops off - making the rocket lighter - and the next stage begins firing.

•At the end, there is just a single stage left, which is the spacecraft.