Newton’s laws of motion

Newton’s Laws of Motion

When a rocket is lifting off from the launch pad, it is because the thrust exceeds the force that is keeping the rocket in place (weight of the rocket and payload caused by Earth's gravity).

The thrust of the rocket engine is greater than the weight of the rocket and the net force accelerates the rocket away from the pad.

This reflects Newton's First Law of Motion, which states that an object at rest will stay at rest as long as no unbalanced force is applied.

When a rocket reaches space, atmospheric drag (friction) is greatly reduced or eliminated.

A rocket traveling away from Earth will eventually escape Earth’s gravity.

Ultimately, the rocket (actually its payload) will travel to the stars. No additional rocket thrust will be needed. Its inertia will cause it to continue to travel outward.

When a rocket is being launched, there are two forces acting on it.

One is the weight of the rocket, the force generated by the gravitational attraction of Earth on the rocket.

The second is thrust, the force that moves the rocket. In general, the heavier the rocket, the more thrust needed to get it off the ground.

The amount of thrust is determined by the mass of rocket propellant that is combusted, creating exhaust, and the speed at which the exhaust is vented from the rocket.

Newton's Second Law of Motion comes into play here, as force (thrust) = mass × acceleration. This formula can also be used to determine the rate at which a rocket accelerates, because acceleration = force/mass.

The movement of the high-speed exhaust in one direction propels the rocket in the opposite direction.

This is Newton's Third Law of Motion in action; for every action there is an equal and opposite reaction.

Thrust has to be carefully controlled when rockets or payloads — like satellites — are launched into space orbit.

Too much thrust or thrust at the wrong time can cause a satellite to be placed in the wrong orbit.

Too little thrust can cause the satellite to fall back to Earth.

Thrust is carefully controlled throughout the launch and maneuvering.

Liquid-propellant engines Propellant for liquid rockets is stored in

large tanks. The propellant components of the fuel and

the oxidizer are stored in separate tanks. The propellant is pumped into a combustion

chamber, where it is mixed and ignited. The propellant burns, creating gases under

high temperatures and pressures.

Liquid-propellant engines The expanding gases escape through the

nozzle at the lower end of the rocket. The nozzle has a narrow throat through which

the exhaust is squeezed. The throat limits the amount of gas that can

escape, causing the gas to accelerate as it leaves the engine (up to speeds of 5000 to 10,000 miles per hour).

As the exhaust is forced out of the nozzle, it propels the rocket in the opposite direction.

Solid-propellant engines The propellant is a dry mixture of fuel and

oxidizer. It is stored in an insulated case. Under normal conditions the propellant does

not burn. Upon launch, the propellant is ignited and

combustion begins. Like the liquid-propellant engines, combustion

of the propellant creates hot, expanding gas that escapes through a nozzle at high pressure, generating thrust.

In space, there is no oxygen, so the space shuttle has to carry its own.

The shuttle uses liquid hydrogen as its fuel. It also carries liquid oxygen. These are combined to produce water and

heat. The steam released propels the rocket in the

opposite direction.

DRAG Drag is the rocket's resistance to motion

caused by the rocket's movement through air. It depends on several factors, including the

density of the air, the shape of the rocket, and the roughness of the rocket's surface.

The more resistant to motion a rocket is, the more thrust is needed to propel it.

The nose cones of rockets are streamlined to help reduce drag.

Model rockets experience drag along their entire flight path because they are moving through Earth's atmosphere. Rockets that move through space do not experience drag because there is no atmosphere.

The thrust must be greater than the weight of the rocket and any drag forces.

Once the model rocket has used all of its fuel, it no longer accelerates. However, Earth's gravity continues to act on this rocket to slow it down.

If the rocket's speed is slow enough, Earth's gravity eventually will pull it back to Earth.

If the rocket's speed exceeds 17,500 miles per hour, it is going fast enough to go into orbit around Earth.

The space shuttle orbits Earth. Satellites also orbit Earth. If the rocket's speed exceeds 25,000 miles per

hour, the rocket is able to escape Earth completely and goes into an independent orbit around our Sun.

Spacecraft that have escaped Earth are exploring other planets and regions of our solar system. Examples of these are the Mars Exploration Rovers and the Cassini-Huygens spacecraft, currently investigating Saturn and its rings.

Rockets must be stable in flight — they must be able to fly in a smooth, predictable direction.

An unstable rocket may tumble or fly in an undesirable (and potentially dangerous!) direction.

Fins help stabilize the rocket. They are lightweight extensions attached to

the exterior of the model rocket. They streamline the flow of air and provide a

large surface area and help to keep the center of pressure behind the center of mass of the rocket.

As rockets have become more advanced, scientists have experimented with fins that they can move during flight to alter the direction of the rocket.

Fins only help stabilize a rocket when there is air present.

In space, the angle at which exhaust is vented is changed to alter the direction of the rocket.

When Alka-Seltzer and water are mixed together, carbon dioxide gas is released in a bubbly reaction.

The release of carbon dioxide provides the thrust of the model rocket engine.

The pressure of the gas eventually builds up until the container cannot hold the gas and the pressure is released by forcing the lid off the container.

This expulsion of exhaust creates thrust to send the model rocket off the ground.