so does tht mean that there is a net downwards force on the
table n does it mean that when i hold something, its heavy becauae
of the contact force on my hand n not because of weight since
weight is acting on the object?
cos of that when n object is hung on the ceiling, there is no
net force, but when i put my hand over to touch the base of the
object i experience contact force but its not heavy? im assuming
this as what u r sayin is that weight acts on the object, n the
floor has a contact force on the weight thus cancellin them out but
then there is still a contact force acting on the ground by the
object so naturally id think that thungs are heavy because of the
contact force and not weight.
so the main questions im askin is whether things are heavy cos
of contact force on the ground? and since there is a contact force
on the ground, would there be a net downwards force?
I did some paragraphing in the quote.
When you find (or rather, you feel) it heavy, yes, it is the
contact force acting on your hand.
The weight of the object acts on the object, and not on your
hand.
Here's a question to test your understanding. If a book is on
your hand and both your hand and the book are accelerating
downwards at 10m/s2, what is the contact force of the book on your
hand?
In physics, we don't talk about whether things are heavy. Heavy
is a subjective word. Instead, we talk about forces. What is the
force of something acting on a body, etc.
When something is on the ground, and not
moving, by newton's second law, there is zero net force.
There is no net downward force as there is no resultant downwards
acceleration. You may treat the ground as a totally immovable
object for O levels.
but in the object hanging on the ceiling case, im not sure if
weight is cancelled by tensional force because i dont know anything
much about tensional force.
Yes. You have to draw the free body diagram of the object with
it's weight and being supported by the tension in the ropes.
finally if the reason y someone can kick off a pools wall is
because there is only an action n reaction force but no weight to
cancel the reaction force on the person n the reaction force is
contact force on the boy?
Yes, the reaction force pushes the person off the pool's wall.
This is a horizontal force.
Weight is acting downwards, and this is balanced by upthrust
from the pool's water. Hence, there is no net movement in the
vertical direction, and the net force on the person is horizontal.
You may treat upthrust as an upwards force due to principles of
floatation. The real explanation and idea of upthrust is in A
levels.
btw eagle, r u a tuition teacher?
Yes. I teach mainly A levels physics and give junior physics
olympiad training to 2 secondary schools.
