Question

Something i read in a book

Answer 1

@Vincent-Lyon.Fr @naveenbabbar

i am wondering what F hg is??

i always thought it was FRICTION.. that allows the horse to move forward

Answer 2

Fhg means the force on the horse by the ground

Answer 3

You are correct.
Fhg meaning force applied by the ground on the horse.

Answer 4

see the note..

i don't understand that note..
what reaction force is F hg ?

Answer 5

but where does that force COME FROM??

shouldn't it be FRICTION????? hwat reaction force is that??

Answer 6

It is friction. That is the only force which helps the horse to move.

Answer 7

if the horse had some frictionless legs or something.. he wouldn't be able to move forward.. and the F hc force would pull it towards the cart.. !!

so i don't understnad why they call it some crazy reaction force.. instead of calling it friction??

or are they just saying friction acts as the reaction force here?

Answer 8

This is correct. Fhg is the forward force that the ground exerts on the horse thanks to friction.

This is a case when friction produces forward acceleration (but, strangely enough, no motive power).

Answer 9

yes i just wantd to confirm that it was friction.. because they didn't mention the word friction :P

Answer 10

If you are considering Fhc the n also consider FCh and both of them are internal forces. Hence in the absence of friction the horse will not be pulled towards the cart.
Also from your question I think you have problem with understanding of internal and external forces and the fact that the forces are mutual.

Answer 11

It is.
It is part of the reaction of the ground since its value adapts to the effort exerted by the horse.

Answer 12

Horse can't move with out external force, which is friction.

Answer 13

Both the answers are correct and convincing. :D

Answer 14

oh yes in this case it can't @naveenbabbar

sorry about that :D

but if i imagine.. pulling on the rope (which is connectd to cart).. then i woudl move towards the cart IF friction between my legs and ground was zero..
and if the friction is HIGHER than the pull that I PUT on the cart, only then.. will i be able to pull the cart towards me (while i stay put .. at rest)

Answer 15

Sounds correct.

Answer 16

Then the external force on you will be the tension in the rope.

Answer 17

Yea so that is the example i would wanna give .. to make students understand HOW i stay put and the cart would come towards me.. EVEN though, from newton's third law, cart pulls me back! :D

Answer 18

If the cart is standing on a frictional surface.

Answer 19

@naveenbabbar
yes yes.. i get the concept of external and internal forces.. in order to evalulate the acceleration of the system (me and cart).. but i was only talking about the concept of third law and why i would stay put!


so in theory .. if i try to push a desk filled with students.. then the desk would weigh a lot.. and thus would have HUGE friction .. so i would have to put huge force..
that is fine.. I CAN PUT THAT FORCE.. but i will not be able to push it because, FRICTION BETWEEN ME and the ground is not enough..
i would wanna give this example with demo in class :D .. its perfect right??

Answer 20

and then.. i would push from the other side (taking the support of the wall) ..

and convince .. that i INDEED have enough muscular force.. to push the desk..

what u think @Vincent-Lyon.Fr ?

Answer 21

This is also what I would do to convince them.
The strongest man (you or superman), without some solid ground (resp. wall) to apply friction (resp. normal) force is powerless.

Answer 22

:D. .. ok .. then i can show some super man video :D..

Answer 23

The problem is that superman pushes without apparent reaction (wall), more like a rocket.

Answer 24

yea the physics behind that.. is very complicated.. xD.. or may be magical