Motion

[Mohit Pandey]

According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. I justify this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why truck does not move.

[Jay-qu]

The truck does not move because you will not be strong enough to overcome the frictional forces in the wheels (or perhaps the brakes are on :naughty: )

 

In an ideal world, with no friction, any force no matter how small will yield an acceleration according to F=ma :)

[ronthepon]

Further, the two equal and opposite forces are by no means cancellable. They act on two different objects.

 

Forces can cancel only if they act on the same body.

 

Tell me, Mohit, By any chance are you quizzing us? Bring it on, then.

[InfiniteNow]

As an aside, two objects never touch, and are subject to forces on subatomic level. (The atoms in) Your hands get really really close to the (atoms in the) truck, but never touch due to the forces acting between them.

 

In fact, the vast majority of ordinary matter is composed of empty space anyway...

 

:naughty:

[Mohit Pandey]

Further, the two equal and opposite forces are by no means cancellable. They act on two different objects.

 

Forces can cancel only if they act on the same body.

 

Tell me, Mohit, By any chance are you quizzing us? Bring it on, then.

 

Ronthepon, about which two different bodies are talking? I could not understand.:confused:

[Mohit Pandey]

As an aside, two objects never touch, and are subject to forces on subatomic level. (The atoms in) Your hands get really really close to the (atoms in the) truck, but never touch due to the forces acting between them.

 

In fact, the vast majority of ordinary matter is composed of empty space anyway...

 

:shade:

 

Which force acts between my hand and the truck? I could not understand your explanation. Please elaborate it.:confused:

[InfiniteNow]

Ronthepon, about which two different bodies are talking? I could not understand.:confused:

Hi Mohit,

 

One body is the truck. The other body is the person pushing on it. These are the two bodies in your example.

 

 

Best,

[InfiniteNow]

I'm having trouble figuring out how much of the confusion is a language barrier and how much is due to a lack of experience on the topic...

 

 

The forces are:

 

Electromagnetism

Weak Force

Strong Force

 

and also gravity, but that would draw the hand and the truck together...

 

Try here for more info:

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980127c.html

 

 

:confused:

[Southtown]

The answer lies in the amount of force. As applied pressure on the truck increases, the first effect of the truck pushing back will be your hands flattening and turning white, then stress on your arms and upper body, ultimately causing your lower body to compensate until traction at your feet fails.

 

The effects of the truck pushing back are biological. The truck doesn't move because it takes around ten-thousand times the force to move a truck than it does to move a human. To illustrate this, picture a human trying to stop a moving truck by standing directly in its path.

[InfiniteNow]

Another answer is the truck doesn't move due to friction and gravity. In the vacuum of space, pushing the truck WOULD move it... Hence the idea of cancelled forces is again negated.

[Southtown]

Oh yeah, good point.

[arkain101]

As an aside, two objects never touch, and are subject to forces on subatomic level. (The atoms in) Your hands get really really close to the (atoms in the) truck, but never touch due to the forces acting between them.

 

In fact, the vast majority of ordinary matter is composed of empty space anyway...

 

That is of course unless you are a Gecko Lizard or have Gecko hands. They have billions of split ended hairs on the millions of hairs on there feet. The actuall hairs are interacting with electron bonds between the material and its feet giving it incredible glue on ANY material it can survive on.

 

Matching this amazing ability will give us the ability to make a type of velcro strong as a weld.

[arkain101]

Pretend the truck is a boat floating on water.

 

If you push on the boat it will move, it will accelerate slowly, but it will move, and you will also move back if you push hard enough with both hands, you will move back more quickly. The boat will move slower.

 

But you and the boat will contain the same amount of momentum.

 

Now for the truck. Everything is the same excpet there is -hidden like- forces acting on the event that will need to be added to the equation, mathamical or logical.

 

You apply a force to the truck, it does not move like the boat because the tires are stuck to the pavement it is parked on. If you push on the truck hard enough with your arms, your body will attain ALL of the momentum generated in the interaction, and you will fall backwards at a velocity greater than you would with an equally massed boat in water.

[InfiniteNow]

That is of course unless you are a Gecko Lizard or have Gecko hands. They have billions of split ended hairs on the millions of hairs on there feet. The actuall hairs are interacting with electron bonds between the material and its feet giving it incredible glue on ANY material it can survive on.

Righteously cool indeed... however, despite the electron bond interactions, they still do not touch. :esmoking:

[Sleeth]

If you take a different example, say for instance a person with rollerskates on pushing against a wall. (The rollerskates are there to minimise friction to an obsolete, so that we can concentrate, just, on the forces involved).

 

The person will 'push' on the wall exerting a force, the wall 'pushes' back against the person and exerting an equal force, opposite to that applied to the wall, 'pushing' the person back!

[arkain101]

Righteously cool indeed... however, despite the electron bond interactions, they still do not touch.

 

I beleive they share electrons with the material, that is as touched as it gets lol.. it is one with the cieling :esmoking:

[arkain101]

If you take a different example, say for instance a person with rollerskates on pushing against a wall. (The rollerskates are there to minimise friction to an obsolete, so that we can concentrate, just, on the forces involved).

 

The person will 'push' on the wall exerting a force, the wall 'pushes' back against the person and exerting an equal force, opposite to that applied to the wall, 'pushing' the person back!

 

I think I see the problem the topic starter was having.

 

yes the truck and the person exter the same equal and opposite force upon eachother, when a person pushes on the truck.

 

The catch is, Only one body can accept the total available momentum possible in the force.

 

There must be this equal opposite reaction in order really anything to behave in a way that is an 'interaction'.