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/sci/ - Science & Math

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6159989 No.6159989 [Reply] [Original]

Suppose in the real physical universe we live in, there is a box on the ground and it requires X amount of force over a time T to move a distance D.

Would it then be true that in TK time under X/K force, it would move D distance where K > 0?

Basically, can I repeatedly tap my index finger on a car parked in neutral billions and billions of times and move it any distance I please?

>> No.6159995

>>6159989
>Basically, can I repeatedly tap my index finger on a car parked in neutral billions and billions of times and move it any distance I please?

no because of friction.

>> No.6160000

It would take more than "billions and billions" of taps to move it depending on the distance you desire, but hypothetically, assuming that there are no outside factors coming into play and you never try to go uphill it could work. There are some situations where your effort would have literally no impact at all, though. For example, if you went up to a mountain side and tapped it trying to move the whole earth I think that the vibration would just be absorbed by the very tiny elastic nature of the rock and probably be canceled out by the force on your legs pushing on the ground in the opposite direction.
So basically, it depends on the specific situation.

But lets say you're in a vacuum with nothing at all in the universe but you and an arbitrarily large massive object, and you are able to somehow tap it with your finger without pushing yourself back as described in Newton's third law of motion, and you had an infinite amount of time to tap the object, then yes, even with very small force you could eventually over time push the object any distance approaching infinity.

>> No.6160005

>>6159995
Even though most of the energy would be absorbed as friction, not 100% of it would be. At least some would be transferred into forward force even if it's really tiny amount.

>> No.6160025

>>6160005
>At least some would be transferred into forward force even if it's really tiny amount.

i think none of it would. we're talking about finger tapping a 4000 lb car. all of the energy would be absorbed by the car's internal structure. you can tap it a billion times and it wouldn't bulge a millimeter.

>> No.6160047

>>6160025
Prove it. Feels vs. Reals.

>> No.6160066

wouldn't you have to pass a threshold force for there to be the start of movement?

>> No.6160079

>>6160000
No - you would never impart enough da/dt to overcome its inertia.

lrn2newton

>> No.6160085

Everyone except >>6160000 (nice grabs or gets or whatever) is just restating the question.

I want to push things with my finger by tapping on it. If I make 10^10^10 taps, do any objects move?

Yes, it's me OP again.

I'm old and I want to push a box of old VCR taped across my waxed hardwood floor. I live on earth. I want to repeatedly tap on one side of the box in a direction parallel to the direction with less obstruction from gravity. Can I move the box at all? Or is it dependent on things? Does it matter?

I can push my friends car with mine at 20 MPH if her car dies and she puts it in neutral.

I can push my friends car with mine at 4 MPH if her car dies and she puts it neutral.

Can't I just apply the same force of a vehicle pushing at 0.0000001MPH with my finger and move the car after a SIGNIFICANTLY large amount of time?

>> No.6160102

Short answer: no.

real physical objects are perfectly rigid entities
the force of tapping leads to microscopy elastic deformations that do not lead to net movement
the forces are no where near enough to overcome the reactive force of friction

you would basically just be jiggling atoms

>> No.6160123

>>6160085
what are you not understanding about friction?

Sum the forces in the X direction.

Its your finger vs the normal force multiplied by the coefficient of friction. If the force of your finger is not greater than the force of friction on the ground, it doesnt matter how many finger taps you do. The box will not move.

from diednt


You learn this in high school physics class.


I bet you will ask if you can run a battery charger using the battery you are charging in the charger next.

>> No.6160137

>>6160102
... are NOT perfectly ...

>> No.6160138

>>6160085
You have to overcome the force of friction before an object can be accelerated.

The force of friction doesn't simply reduce the effectiveness of the force caused by your tapping, it presents a barrier that needs to be exceeded before any acceleration happens.

In the case of a non-moving object, you have to overcome the static friction.

In the case of an already-moving object, you need to overcome the kinetic friction in order to accelerate the object above its current velocity.

Think of friction as a an equal-but-opposite force that automatically increases to match the force of your tapping, except it has a maximum value (which is the coefficient of friction * the weight of the object). The coefficient of friction depends on the conditions of the touching materials.

>> No.6160499

>>6160138
So I just push harder then?

>> No.6161777

>>6159989
no, most of the energy would be dissipated as friction in deformation of the structure of the car. even if the car itself was rigid, you would never overcome the static friction between car and ground, which would also be dissipated as heat. no motion.

>> No.6161792

>>6160499
Yyyyyeeeeep.

>> No.6162011

>>6160047
Static friction. Even at the atomic level with perfectly atomically smooth surfaces you can't avoid friction.

>> No.6162262

>>6161777
What about how quickly you tap the car? Could you at least tap it fast enough to damage it?