If gravity is one force ,where is the other force of reaction?

Question

So gravity must be a bi-force.Since force cannot exist by its self any more that a magnetic pole can exit by itself?Unless Newton's 3rd law of motion is incorrect?

Answer 1

yup you are right. The force requires matter. Like a tree in the forest falling. Sound waves are created but if no one hears it does it really exist?

Answer 2

There are two cases which must be examined to answer your question.

- Case 1: An object falling towards a massive body (Earth for example) due to the effects of gravity.
- Case 2: An object resting on the surface of a massive body.

In both cases, gravity affects the object and in both cases, Newton's 3rd Law holds true.

Case 1:
When an object falls towards the Earth, it continues to accelerate due to the [seemingly] "unbalanced" force of gravity acting on it. The force of gravity acting on the object (its weight) causes an acceleration on the object.
But remember, gravity works both ways. Just as the Earth is exerting a force on the object, the object is exerting a force of the exact same magnitude on the Earth on the opposite direction. As the object accelerates towards the Earth, the Earth accelerates towards the object. Since the mass of the Earth is so huge compared to the mass of the object, the Earth's acceleration is often ignored since it is so miniscule, but it does exist.
When one takes into account the Earth's acceleration, both Newton's 3rd law of motion AND the law of conservation of momentum are satisfied.

Case 2:
When an object rests on the ground, gravity is still exerting a downward force on the object (as is the object on the Earth)....but in this case, the object is not accelerating.
According to Newton's 2nd law, F = ma, if there is no acceleration, the net force must equal zero. This would make sense since there must be an equal and opposite force (according to Newton's 3rd law) to balance the object's weight. This balancing force is called the "Normal Force" as it is exerted by the surface the object rests on in the "Normal" direction (i.e. the opposite direction as the force of gravity is acting). This normal force has the same magnitude as the object's weight and is pointed in the opposite direction, thus Newton's 3rd law is again satisfied (as well as Newton's 2nd).

Answer 3

Excellent observation "for every action there is an equal and opposite reaction".

First, notice that the force of gravity is an energy source. There seems to be some confusion concerning this, so I'll quote a person most believe to be a final authority, Stephen Hawking. On page 92, para 3; "Like light, gravitational waves carry energy away from the objects that emit them." In order for this to happen there has to be an expenditure of something. If this were not true, then this force is being created in all matter at all times. Our planet expends 0.00444 kg. sec in gravitational waves in order to keep everything in place. Our sun expendeds 665 lbs. of gravitational frequencies every second in order to keep the planets where they are supposed to be.

Notice that all solar bodies are spheres. The reason for this shape is that the mass is being drawn inward due to the heat energy within them. Asteroids are able to be any shape. Heat them to a molten state and they, as the planets and our sun, assume a spherical shape.

The compression of the mass changes the shape of individual atoms forming it. This change causes gravitational waves to form. Below the "Moho" discontinunity, mass directs all waves through the core point of our planet. Thus mass on one side of our planet pulls all mass on the other side with equal force and our planet becomes a sphere. Notice that these waves attract the heat energy within our planet toward its center as well as the mass on its surface. If this were not true, then our planet would become almost a single temperature througout.

The "action, reaction" exists on either side of our planet. That mass which is keeping us of the United States in place exists in the Indan Ocean. Likewise, the mass of the United States is keeping that ocean where it is supposed to be.

Answer 4

Yeah, look at Newtons laws of motion to learn the basic forces of nature. A body at rest staying at rest , one in motin staying in motion, etc.

Newton was BRILLIANT. He figured out lots of stuff while sitting and eating breakfast ceral without formal training at first. Then he read everything he could. Borrowed books without asking sometimes I think. Books were rare and valuable in his time. Also , he made a hole in the roof and studied the beam of light with prizms, thermometers etc. He discovered infrared invisible light. Check out Optiks maybe. Maybe Huxleys "On a piece of chaulk" too.

Answer 5

The reaction is the force you place on the Earth's surface. If in space and you are attracted by gravity the reaction is the resulting impact.

Answer 6

The force of gravity pulls you toward the center of the earth. The earth pushes you back with the same force that it pulls you with.

There you have it, equal and opposite reactions.

Answer 7

The force you are referring to is force normal i suppose. When an object is standing on a surface, the surface exerts normal force on the object to keep it in position.

Answer 8

In space - you know

Answer 9

the other force is inertia.

Answer 10

cuze God said so...duh!