forces and motion question

[hyperlight49]

I have a question about the physical interaction of objects (not physical properties, but forces that move thing), what do we call that? Also, what does the third law of motion (action-reaction) have to do with the earth, a wall, a floor, a table and moving through a medium (like air)?

[ecoli]

I have a question about the physical interaction of objects (not physical properties, but forces that move thing), what do we call that?

 

Do you mean the four fundemental forces? Natural Force, Gravitational Force, Applied Force, and Force of Friction.

 

Also, what does the third law of motion (action-reaction) have to do with the earth, a wall, a floor, a table and moving through a medium (like air)?

 

In what context?

[hyperlight49]

Do you mean the four fundemental forces? Natural Force, Gravitational Force, Applied Force, and Force of Friction.

 

You know, the force that's a push and a pull, but those could work.

 

In what context?

 

Just give me some examples please.

[ecoli]

well, a ball thrown at a wall will bounce back at an opposite angle you throw it at. In order to jump up, you first have to push down, against the earth.

[Klaynos]

if you put a box on a table the force the box is exerting on the table will be it's weight due to gravity, and the force the table exerting on the box is exactly equal to this but upwards instead of downwards. In the same way the table is pushing down on the floor, and the floor is pushing up against the table with exactly the same force.

[ecoli]

Which is why the box stays still, and doesn't move up or down.

[swansont]

Note, however, that zero net force doesn't imply it's sitting still.

[swansont]

if you put a box on a table the force the box is exerting on the table will be it's weight due to gravity, and the force the table exerting on the box is exactly equal to this but upwards instead of downwards. In the same way the table is pushing down on the floor, and the floor is pushing up against the table with exactly the same force.

 

The force the box exerts on the table is not its weight. It will have a magnitude equal to its weight in this case, but the force that the table and box exert on each other is a contact force, and weight is a gravitational force.

 

However, the contact forces in this example are known as action/reaction forces. They are always of the same type. The gravitational force the earth and box exert on each other would likewise be an action/reaction force pair.

[ecoli]

Note, however, that zero net force doesn't imply it's sitting still.

 

Just zero acceleration.

[Dave]

=> constant velocity (which may or may not be 0).

[Guest Mr.Therefore]

I have a question about the physical interaction of objects (not physical properties, but forces that move thing), what do we call that?

 

That is inertia. But, inertia is a property of the object, not what pushes it. It seems you imply there must always be a cause and effect occuring. But this is not inertia, this is force.

 

We begin by learning the concept of interia, which means the object is not having a change of speed or direction. An object demonstrates inertia only two ways: it must be at rest or have a constant speed and constant direction. (Inertia is hard to conceptulize I think, because our entire lives are filled with experiences with objects in frictive mediums, meaning they don't move in according to the concept interia, they accelerate and deccelerate all the time.)

 

When we think of what does "push" it we only mean "force". "Push" requires two things touch. "Push" cannot occur unless two things are colliding. "Force" means two things collide. When an object expresses force it must have a change of speed or direction.

 

An object may not express both interia and force simultaneously. It is one or the other. And these are the only two categories of expression.

 

When two things "push" "collide" or express "force", we could choose what point of view we say it:

 

Object A is exerting a force on Object B.

 

Object B is exerting a force on Object A.

 

The fact is, they both exert a force on each other simultaneously. Why?

 

A collision cannot occur unless both things are touching. Where there is no collision, no force can be applied. Where no force is applied, only inertia exists with both objects.

 

(Substitute "push", "collide" for "force" in the previoius sentences to get a further understanding that they are equivalent in principle meaning.)

 

There is a common misconception when learing these two concepts.

 

The object that continues to move in the direction it moved after the collision is the only one to apply a force in the circumstance, because of the result that the other object is now moving in the opposite direction.

 

Becarefull not to make this mistake. To understand why this is false, the concepts of intertia and force must be thoroughly studied and distinguished. When you understand the difference, you'll go back to that question and ask yourself, "What was I really thinking?"

 

I was there.