They adjust variables and investigate how height and speed are affected. View a launch of a space shuttle. Note the time, speed and altitude at each stage of its journey. Add to collection. Related content Explore further some of the ideas that are fundamental to understanding rockets: Lift-off Rockets and mass Getting rockets into space Activity ideas Explore using the Rocket launch challenge interactive in the Rocket launch challenge activity.
Useful link View a launch of a space shuttle. Go to full glossary Add 0 items to collection. Download 0 items. Twitter Pinterest Facebook Instagram. You have things like:. But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in. Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively see the links on the last page of the article for details.
On the other hand, rocket engines and their fuel systems are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them. For example, a reciprocating gasoline engine in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction. This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening.
Rocket engines seem to be about flames and noise and pressure, not "throwing things. Tune in to the Turbo Channel -- the place to be for programming about cars, motorcycles, planes and everything else with a motor.
Imagine the following situation: You are wearing a space suit and you are floating in space beside the space shuttle ; you happen to have a baseball in your hand. If you throw the baseball , your body will react by moving in the opposite direction of the ball.
The thing that controls the speed at which your body moves away is the weight of the baseball that you throw and the amount of acceleration that you apply to it.
So let's say that the baseball weighs 1 pound, and your body plus the space suit weighs pounds. You throw the baseball away at a speed of 32 feet per second 21 mph. That is to say, you accelerate the 1-pound baseball with your arm so that it obtains a velocity of 21 mph. Your body reacts, but it weighs times more than the baseball.
Therefore, it moves away at one-hundredth the velocity of the baseball, or 0. If you want to generate more thrust from your baseball, you have two options: increase the mass or increase the acceleration. You can throw a heavier baseball or throw a number of baseballs one after another increasing the mass , or you can throw the baseball faster increasing the acceleration on it.
But that is all that you can do. A rocket engine is generally throwing mass in the form of a high-pressure gas. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns.
The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas.
The form changes, but the mass does not. The burning process accelerates the mass. The "strength" of a rocket engine is called its thrust. Thrust is measured in "pounds of thrust" in the U. A pound of thrust is the amount of thrust it would take to keep a 1-pound object stationary against the force of gravity on Earth. So on Earth , the acceleration of gravity is 32 feet per second per second 21 mph per second. If you were floating in space with a bag of baseballs and you threw one baseball per second away from you at 21 mph, your baseballs would be generating the equivalent of 1 pound of thrust.
All of these variables depend on the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle.
The hot exhaust flow is choked at the throat, which means that the Mach number is equal to 1. The area ratio from the throat to the exit Ae sets the exit velocity Ve and the exit pressure pe. You can explore the design and operation of a rocket nozzle with our interactive thrust simulator program which runs on your browser.
Click to run the simulation. Conceptual Questions Professional Application. Suppose a fireworks shell explodes, breaking into three large pieces for which air resistance is negligible. How is the motion of the center of mass affected by the explosion? How would it be affected if the pieces experienced significantly more air resistance than the intact shell?
Professional Application. During a visit to the International Space Station, an astronaut was positioned motionless in the center of the station, out of reach of any solid object on which he could exert a force.
Suggest a method by which he could move himself away from this position, and explain the physics involved. It is possible for the velocity of a rocket to be greater than the exhaust velocity of the gases it ejects.
When that is the case, the gas velocity and gas momentum are in the same direction as that of the rocket. How is the rocket still able to obtain thrust by ejecting the gases? Antiballistic missiles ABMs are designed to have very large accelerations so that they may intercept fast-moving incoming missiles in the short time available.
What is the takeoff acceleration of a 10,kg ABM that expels kg of gas per second at an exhaust velocity of 2. What is the acceleration of a kg rocket taking off from the Moon, where the acceleration due to gravity is only 1.
Calculate the increase in velocity of a kg space probe that expels kg of its mass at an exhaust velocity of 2. Ion-propulsion rockets have been proposed for use in space.
They employ atomic ionization techniques and nuclear energy sources to produce extremely high exhaust velocities, perhaps as great as 8. These techniques allow a much more favorable payload-to-fuel ratio. To illustrate this fact: a Calculate the increase in velocity of a 20,kg space probe that expels only Calculate the acceleration of such an engine if it expels 4.
Derive the equation for the vertical acceleration of a rocket. The mass of the rocket just as it runs out of fuel is 75,kg, and its exhaust velocity is 2. Given the following data for a fire extinguisher-toy wagon rocket experiment, calculate the average exhaust velocity of the gases expelled from the extinguisher.
Starting from rest, the final velocity is
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