Questions tagged [free-body-diagram]
A pictorial device which analyzes forces present on any body with the use of vectors. Allows easier grasping of problems involving either objects at equilibrium or in motion. Can be used to predict presence of forces.
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Why friction of a wheel is zero? [duplicate]
MY physics teacher told us that friction is independent of surface area. but Also said that friction in a wheel is zero because the surface of wheel is in contact with wheel for only small amount of ...
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Does Newton's 3rd law hold true everytime? [duplicate]
Well,I know (and was also told) Newton's third law is just conservation of momentum in disguise.
And momentum is only conserved in a system when $\sum F_{ext}=0$.
Alright,suppose there is a system of ...
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How to calculate tension in this case? [closed]
I came up with this idea while learning rotational motion.
Note:
I have not found any question on it but its a concept I want to know.
Take a rod of mass M and length L. Hang it with cealing using ...
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Can a sand hill be modelled as an inclined plane? [closed]
I have modelled the sand pile as an incline plane that in in of itself im questioning whether is a right decision
i was kinda confused will friction act up or down the incline on the grain of sand ...
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Role of Friction in Pure Rolling
Consider a Sphere performing Pure Rolling on a rough surface.The velocity of centre of mass of sphere is towards right and it has a clockwise angular velocity,with acceleration of centre of mass a and ...
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What is the relation between rope length, object weight and force needed?
Whenever I pull an object from a rope or cable, the weight never really feel the same depending on the rope length, and I would like to understand why, and learn more about the maths behind this.
So, ...
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I would like to calculate the lifting force required to stand up my motorcycle after laying it down on its side (real life scenario after a crash) [closed]
What would be the formula used to calculate the force required to lift a fallen motorcycle (assume a uniform mass...no lever effect) that weighs say 550 lbs? The answer is obviously angle-dependent......
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Two different versions of Newton's Third Law
I have two different versions of Newton's Third Law.
Newton's Law is simply a way of describing forces. When a moving Object A, hits Object B and transfers all its energy to B, Object A stops because ...
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Equilibrium of a ladder kept leaning against a wall [closed]
If a ladder is kept leaning against a wall as in the picture, how to determine the direction of,
i) The force exerted by the wall on the ladder?
ii) The force exerted by the floor on the ladder?
And ...
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Is the person in the picture doing any work? [duplicate]
"In figure (i) the man walks 2m carrying a mass of 15kg on his hands. In figure (ii) he walks the same distance pulling the rope behind him. The rope goes over a pully and a mass of 15kg hangs at ...
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Case study on inertia
When our upper body and lower body both are in contact with bus then after applying breaks why only upper body part moves forward?
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How is mechanical energy conserved in inclined plane-block system?
This is a rather standard problem where there is an inclined plane (of mass M) on a frictionless horizontal surface and a block (of mass m) slides on it. The problem asks us to calculate the speeds of ...
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Stacked block problem & static friction
For the two-block problem below, why is the static friction not equal to applied force when both blocks move with same acceleration?
I mean that in physics it’s taught that static friction is always ...
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Confusion in kinetic and static friction difference and approaching problems
Is the friction here kinetic since the blocks are moving down. I don't know how to know when to apply kinetic friction and when to apply static fricion. When motion is givien I understand and use ...
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Does the elastic potential energy belong to the spring, or the object attached to it (or both)? [duplicate]
I was taught the elastic potential energy was stored in the spring
but then one practice problem on my textbook suggests the potential energy is in the object that is compressing the spring:
A $42 \,\...
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Why do we have an opposing force in dynamic equilibrium? [duplicate]
I found this definition in my textbook about how dynamic equilibrium works. I was wondering if the opposing force is equal to the given force such that the net force is 0. Wouldn’t that mean that the ...
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A Monkey-Pulley Problem [closed]
A Monkey of Mass $M$ is hanging on one side of a pulley with a box of Mass $M$ hanging on the other side.
Part (A) The monkey climbs up height $h$ with respect to the pulley. Find the work done by the ...
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Increase in tension due to weight
Suppose string is hanging from two hooks. We now add a weight $W$ to its midpoint the string will bend and the resulting tension in the string will be given by $W/2cos \theta$ where $\theta$ is the ...
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If pressure is caused by the weight of water above you, why is pressure said to act in all direction, not just down?
I don’t think I have worded my question very well. Here’s another try…
We are taught that pressure of a fluid increases with depth, usually given the explanation of the increasing weight from the ...
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How does one start swinging on a swing/hammock? [duplicate]
Let's say Alice is sitting on a swing/hammock, in its rest position. In order to start swinging, she moves her body in the way everyone knows how to do, to start swinging. From a conservation of ...
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How does Newton's third law apply to forces between fluids and solid surface?
What is the direction of the force exerted by the fluid on the solid surface and what is the direction of the force exerted by the solid surface on the fluid?
If I am not wrong, I think the force ...
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Does spring stop applying force as soon as we cut it?
Does spring stop applying force just after we cut it? Like in this image will $F'$ be zero?
The question arises because i have solved a few problems in which it says we cut the spring but we ...
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What is the absolute Value of Normal force on a block on Wedge?
So i have been solving problems of Newton's Laws of motion and this thing has been quite conflicting for me. I wont complicate my question. I just need one answer.
What is the absolute value of normal ...
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An elevator is falling, there is air resistance outside, would a person inside fall to the floor? [duplicate]
An elevator is falling, as in the real world, with some air resistance outside slowing the fall.
There is a person inside the elevator. Would the person experience some force pulling them towards the ...
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When is Normal force 0?
Let's say 2 bodies are in contact and are placed on a frictionless surface, both of them being at rest, so there isn't any normal contact force acting between the 2 bodies. So my question is even ...
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Wedge constrained motion problem [closed]
I was solving this question on wedge-constrained motion:
Q)Acceleration of blocks A and C are 2a and 3a respectively.
Find the acceleration of block B.
My Approach:
Below I'm attaching a diagram ...
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Person holding two persons hanging over the edge and centre of mass inconsistency
Imagine a person holding the leg of the person in front that also holds the person in front of him. (over the edge like in MI4, assume centre of mass of second person with feet still on the floor is ...
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A bird in a container [duplicate]
Suppose there is a bird in a sealed container, and the container is on a scale that measures its weight. The bird is flapping its wings to hover in the middle of the container. If the bird flaps its ...
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Why can we treat a ball as a point mass to calculate torque?
A sphere of radius $R$ is supported by a rope attached to a wall as shown in the below figure. The rope makes an angle $\theta$ with respect to the wall. The point where the rope is attached to the ...
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A paradox while explaining the equilibrium of books
An even number of books (say four) are held in the manner shown in the figure. It is obvious that if we apply a large force inwards, we can increase the normal force, and hence the friction which ...
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Tension of rope over frictionless edge obstructing block
Consider the diagram below. All corners are assumed to have no friction. Is it true that the tension throughout the rope is equal in all sections? The section over the edge of the building, the ...
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Condition for a car moving with a constant velocity [closed]
I seek your help with this simple yet confusing problem. The question says:
A car is moving with a constant velocity 10m/s. Which one is correct?
No force is acting on the car
The force applied by ...
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When an object is thrown towards the sky it starts to gain potential energy, why?
I didn't think so because when an object is thrown towards the sky it already has kinetic energy and it looses it's energy due to the gravitational force of the earth.
When the object looses all of it'...
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What does $v$ actually represent in pulley problems?
Let us consider the problem of two pulleys with boxes attached to their ends. One pulley is movable, and the other is not. The problem requires us to find a relationship between velocities of these ...
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Is there any phenomenon where opposite reaction (Newton's 3rd Law) is not fulfilled?
I'm wondering if there is any case in nature/physics where it has been observed "where there is an action, there is not necessarily an exact equal and opposite reaction".
Or is there some ...
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Why does the counterweight actually go up?
So, let's consider a simple ideal pulley system where there's a weight to be pulled, and a counterweight on the other side
According to my understanding (feel free to nitpick), there's a restoring ...
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Statics problem from classical mechanics
I was solving David Morin's book on classical mechanics.
In the solution for the second part of the "a" part of the question, why is the normal force defined as $Ndθ$ and not just $N$? Is ...
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How Does Hydrostatic Pressure Account for Liquid Layers That Can Mix?
I'm trying to understand how pressure in a homogeneous fluid at a given depth is determined by the weight of the fluid above that point. Specifically, I am confused about how the weight of the liquid ...
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Why do objects slow down when they hit the ground? [closed]
Say you drop an object on the ground. For the purpose of this question, I am just focusing on the slowing down of the object, not if it rebounds. I was just wondering which of the two reasons explains ...
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Why Does Tension Differ in Sections of a String Around a Pulley and Blocks?
Why is the tension $T_1$
of the string the same at all points between block A and pulley B but not the same between block A and block D? The text mentions that
$$T_1≠T_2$$
, unless pulley B is light, ...
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Tension in a massless string in various configurations [duplicate]
If a massless string is stretched by applying extensive forces of magnitude $x$ on both sides, a tension $T$ is developed at every point of the string. If the same massless string is placed over a ...
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Tension in Atwood machine revisited
In their book "Theoretical Mechanics of Particles and Continua", Fetter and Walecka ask to solve the problem (problem 1.3 of Chapter 1) of an Atwood machine in which a massless string is ...
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How does a vehicle's brake affect the friction between the vehicle and ground?
When brakes are activated in a vehicle it decelerates. Analysing its motion, there can be only one force that can be responsible for it: the friction between the car and the ground.
So does braking ...
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Problem with internal forces in spring following Hooke´s law
When looking at Hooke's law for the entire spring the force is $kx$.
But what happens when analyzing segments of the spring in order to look at the internal forces?
Imagine a spring of length $x$ that ...
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Where am I wrong in proving that force perpendicular to motion increases speed and kinetic energy? [closed]
Lets think of a helicopter flying at some height $h$. It throws a food packet to a person on the ground from air. Let's neglect the air drag.
The food packet is thrown only with some velocity $v_x$ in ...
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Is the work I do on the object always equal in magnitude but opposite in sign to the work the object does on me?
According to the definition of work, the work I do on an object is equal to the force I apply to the object multiplied by the distance the object moves. By Newton's third law, the reaction force (F21) ...
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Why, when we calculate forces in banking of roads, we do not take the centripetal force but the centrifugal force?
I know the we only apply centrifugal force when in non inertial frame of the object but in banking of road questions, why cant we make equations from inertial frame rather than non inertial frame?
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Two weighing scales compressed inside a solid frame
Two weighing scales are placed on top of each other at the bottom of a solid enclosed frame.
At the top of the frame a linear actuator is attached.
The linear actuator can extend and press down upon ...
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Drawing a free-body diagram for a body residing on Lagrange point $L_4$ and $L_5$
I am aware of the fact that Lagrange points $L_4$ and $L_5$ are stable equilibrium points however I cannot understand why they are equilibrium points in the first place.
Consider a Earth-Moon system ...
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If you're holding on to a playground spinning wheel and then let go, is your trajectory straight or curved?
Let's say you are on one of those playground spinning wheels and then you let go. I've heard that you will fly off tangentially to the wheel, but do you really fly off in a straight line, since you ...
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