No I wrote it in my words and yes there is F.BvU said:
BvU said:
Would I be correct to assume that ##\vec{F}## is, as drawn, purely horizontal?rudransh verma said:
Force on B is balanced from all directions but not on A. There is no upward friction since the wall is smooth. So the system assuming is at rest in beginning cannot remain in rest and is not in equilibrium if that what we mean by equilibrium (rest).jbriggs444 said:
Q1. How do you know? What are the forces on B? What balances B's weight?rudransh verma said:
Q2. How do you know? What are the forces on A?rudransh verma said:
Q3 If A and B start at rest, do you think B (which you think is in equilibrium) remain at rest?rudransh verma said:
Surface A and B are rough. Friction.Steve4Physics said:
Wall is smooth.Steve4Physics said:
After A slips B will too eventually.Steve4Physics said:
I think there is no acceleration.Steve4Physics said:
No!Steve4Physics said:
Why not immediately? What is holding it in place?rudransh verma said:
Body Ajbriggs444 said:
How is body A supposed to support body B if body A is, itself, falling down?rudransh verma said:
I meant momentarily.jbriggs444 said:
Q1. If A moves down and IF there is friction,between A and B there would be two downwards forces on B (weight and friction from A). So B would not be in equilibrium.rudransh verma said:
Q2. But IF A exert a frictional force on B, then B exerts an equal magnitude and opposite direction frictional force on A (Newton’s 3rd law). So B would exert a frictional force on A (even though there is no frictional force on A due to the smooth wall).rudransh verma said:
Q3. Why ‘eventually’? What will make B start to move?rudransh verma said:
Q5 You haven’t answered the question asked.rudransh verma said:
P.S. How much gravitational potential energy did the knife lose in total? How much work did the resistive force do? If you can answer those two questions you can find the resistive force extremely easily.rudransh verma said:
Static friction?rudransh verma said:
Frictional forces act to oppose the relative motion that occurs, or would otherwise occur, between surfaces in contact.rudransh verma said:
Yes, they both fall. Do they fall at the same rate?rudransh verma said:
Your diagram is wrong. And the blocks are not in equilibrium.rudransh verma said:
Gavity is acting on the stone.Steve4Physics said:
Will the (frictionless) blocks fall at the same rate? What is this rate?rudransh verma said:
No! Different rate since difference in mass. Acceleration due to gravity!Steve4Physics said:
yeah!Steve4Physics said:
What supporting forces? are you talking about normal forces and friction?Steve4Physics said:
There are none. We expect that the blocks begin at rest relative to each other because we are not told otherwise. We might imagine that this was arranged by having the blocks held in place until just before we start looking at the system.rudransh verma said:
No, not different rates! Identical rates!rudransh verma said:
Suppose blocks A and B are initially stationary and each hang on a string.rudransh verma said:
O right!Steve4Physics said:
Due to weight of B there is upward friction on A but due to weight of A there is downward friction on B. So both will come down the moment they are released at same rate g.Steve4Physics said:
I think there should be no friction too because there is no upward force on any of the bodies.BvU said:
But there is a downward force on both bodies. What makes upward forces special in your mind?rudransh verma said:
There have to be relative motion between A and B for the friction to occur here. Wall is smooth and no upward force on B. So both will fall at same rate due to gravity after we remove supporting forces.jbriggs444 said:
As I wrote, that is for kinetuc friction. For static friction there does not need to be any actual relative motion, only that there would be relative motion if the friction were not there.rudransh verma said:
No. That's only true for kinetic friction. I will add to @haruspex's comment...rudransh verma said:
O yeah! But there is also no static friction here because of the absence of any upward force. Both will fall as one system.Steve4Physics said:
Yes indeed! If you read through the previous posts, you will see that this is the message we have been trying to convey!rudransh verma said:
A system of two bodies and wall refers to a physical system consisting of two objects or bodies interacting with each other and a third object, typically a wall, that serves as a boundary or constraint for the system.
Some examples of a system of two bodies and wall include a pendulum swinging back and forth between two walls, a ball bouncing between two walls, or two objects colliding with each other against a wall.
The motion of a system of two bodies and wall is determined by the initial conditions of the system, such as the mass, velocity, and position of the two bodies, as well as the properties of the wall, such as its elasticity and surface friction.
Studying a system of two bodies and wall allows scientists to better understand the principles of mechanics and the behavior of objects in motion. It also has practical applications in fields such as engineering and physics.
The presence of a wall can affect the motion of a system of two bodies in various ways, such as limiting the range of motion, causing changes in velocity or direction, or transferring energy between the bodies. The properties of the wall, such as its rigidity and surface characteristics, can also impact the behavior of the system.
