as he ruduces the thrust how does the foward force now compare with the backward force?
465068
As the plane's engines provide thrust, there is a certain amount of force countering it in the form of drag. So if the thrust from the engines were to drop off, the drag force would be greater than the forward force. (Eventually, the drag force will also be reduced so that the two opposing forces will be in balance again.) Because of this, the plane will immediately start to decelerate.
555212
Yes, velocity is changing it's direction as well as magnitude. Acceleration due to gravity is acting downward.
733139
It follows Newton's law that for every action there is an equal and opposite reaction.  It's usually a wheeled vehicle that flings something backward in order to move forward.  The simplest type uses the jet of air escaping from an inflated balloon.
275035
There is more friction on re-entry. Friction is geometrically proportional to speed. The shuttle takes a long time to accelerate into orbit, but it comes back full speed. Also the flight angle is diferent on re-entry, exposing more surface.
1053103
Podkletnov has demonstrated a number of laboratory devices that supposedly work by antigravity.  I'm not sure what he's claiming lately, but his original work claimed a reduction in gravitational force of 2%. So far, apparently, no one has been able to replicate his results.\n\nAlso, in the absence of a solid theoretical analysis, it is possible that he is really generating some other type of force. For example, T. Townsend Brown's "lifters", long a favorite of antigravity hobbyists, are actually ion wind devices.
1010543
Suppose you are taking a space walk near the space shuttle, and your safety line breaks. How would you get back to the shuttle? The thing to do would be to take one of the tools from your tool belt and throw it is hard as you can directly away from the shuttle. Then, with the help of Newton's second and third laws, you will accelerate back towards the shuttle. As you throw the tool, you push against it, causing it to accelerate. At the same time, by Newton's third law, the tool is pushing back against you in the opposite direction, which causes you to accelerate back towards the shuttle, as desired. This is the principle behind jet propulsion: a jet rocket expels fuel rapidly by ``pushing against it''. By the third law the fuel exerts an equal and opposite force against the rocket so the rocket accelerates in the opposite direction that the expelled fuel goes. Another example of the 3rd law is a book lying on a table. If the table were not there the book would fall under the force of gravity between the book and the earth. Why then doesn't the book move off the table, in accordance with the 2nd law? The table is exerting a force on the book that is just enough to cancel the gravitational force on the book. By Newton's third law, the book is also exerting an equal and opposite force on the table, and this is why the table feels the weight of the book. If the book were very heavy, its weight would cause the table to bend, or even break. This is illustrated in the following figure. \n\nThe answer to this question comes from the third law. Imagine the skateboard again. On the ground, the only part air plays in the motions of the rider and the skateboard is to slow them down. Moving through the air causes friction, or as scientists call it, drag. The surrounding air impedes the action-reaction. \n\nAs a result rockets actually work better in space than they do in air. As the exhaust gas leaves the rocket engine it must push away the surrounding air; this uses up some of the energy of the rocket. In space, the exhaust gases can escape freely.
647302
Thrust is the reactive force that is exerted by a rocket, propellar, or jet engine, which propels a craft.
360222
Interesting question.  I'll give a hand waving argument.  Assume the Theory of Relativity is true.  I'm not so sure I believe it, but assume it is true.\n\nYou start your trip with a certain amount of fuel, which you thought would be sufficient using the ordinary laws of classical physics. As you accelerate you have to use fuel.  To you there is no increase of mass, no increase in fuel.  You feel the acceleration, and that is all.  However, after awhile it seems that you are not gaining velocity relative to the "stationary" stars as you thought you should be.  You keep using up your fuel, of whatever type you brought with you, and you continue to feel the same force of acceleration that you did, but it seems to be having less and less effect in getting you up to the velocity you want.  Eventually you run out of fuel, at something less than the speed of light relative to the earth you left.  What went wrong?  It takes more and more energy to increase velocity with respect to the earth, because with respect to earth your mass has increased, though as far as you are concerned you cannot measure any increase in your mass.  It is just the fundamental paradox of the Theory of Relativity.
282006
Answer is 'acts in the direction opposite of motion."\n\nFriction always opposes motion. Therefore first one is wrong.\nFriction is equal to mu times the weight. and mu is not equal to one.Therefore second  one is wrong.\n Sliding friction is less than static friction\nTherefore Third   one is wrong.
673422
good question. the one with air cuz it has more mass
903133
From what I learned in physics class, the force you are speaking of is measured in Newtons.
888539
its impulse change in momentum
87065
To slightly correct the previous answer, the 2 opposing forces are on different bodies. The ball experiences an outward force, and the bat an inwards force. Its the complete system that experiences cancelling forces, not the individual bodies participating.
780140
The forces are equal and opposite, but your friend with twice your mass will accelerate at only half the rate you do.  Newton's Third Law of Motion specifies that any action (i.e., force) has an equal and opposite reaction, in this case the force with which your friend pushes on you when you push on him.  Newton's Second Law of Motion says that the rate of change of momentum is proportional to an applied force.  This is usually rendered F = ma, where F is force, m is mass, and a is acceleration.  As you can see, to keep F constant when m is doubled, a must be divided in half.
514064
It's about the conservation of the momentum (impulse).\n\nIf it accelerates, the exhaust gas has a speed in a direction; this will give the spaceship a certain speed in the other direction (the ratio of speeds will be equal to the ratio of gas/spaceship mass)\n\nIn any other case, it will keep the current velocity and direction as there is nothing to slow it down (there is no athmosphere) - unless it bumps into something.
200339
Conservation of momentum.  Newton tells us that for every action, there is an equal and opposite reaction, such that in a collision, the net momentum remains the same.  When you realese gas backwards, the momentum imparted on the gas away from the space craft needs to be ofset by imparting momentum upon the astronaut in the direction of the space craft.\n\nWhen you fire a gun, the momentum of the bullet forward is equal to the momentum of he gun backward.  Since the gun is much bigger than the bullet, it doen't move as fast, and the force is spread over a larger asrea (your hands and shoulder).  But the kick backwards is the same sort of principle: the equal and opposite reaction.
819561
Perhaps surprisingly, the ballon will move forward (relative to the car). There are two ways to see this. One is the principle of equivalence: acceleration is like gravity, and in this artificial gravity field (directed backwards) there is a buoyancy force on the baloon (it's lighter than air). Or you could say a pressure gradient, directed forwards, has to build up inside the accelerated car (to accelerate the air), and this pressure will drive the ballon forward (the pressure is just enough to keep the air accelerating with the car, but the balloon is lighter than the air it displaces so it gains an extra acceleration).