# 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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### Does the normal force require other forces to exist?

Let's say we have two blocks resting over a frictionless surface. The two blocks are next to each other and there is contact between them. Even though there is no force trying to push them closer to ...
66 views

### Tension produced from a string junction

When you have three light strings connected at a junction, and you create a tension in one of them, as seen here; (There're masses attached to the ends of the other two cords, not shown in the figure....
1k views

### Applying force in zero seconds? How is this possible?

$F\,\Delta t=m\,\Delta v$, is the equation of impulse. Let's say that I push a wall with my hands, we can have $0$ change in velocity; therefore, $F\,\Delta t=0$, since I'm pushing the wall there is ...
23 views

### Clarification of FBD in Head on Car Crash [closed]

Two identical vehicles (of the same size and mass) travel at the same speed, in opposite directions, and they collide with each other head-on. If we only look at the forces from the cars only then: ...
21 views

### How to find the of inclination [closed]

I solve this problem by using equilibrium condition
23 views

### Different Values of time coming when we consider different components of acceleration [closed]

In the given figure , we need to find the time when the block strikes the vertical wall. If we go to the reference frame of the block, the only downward acceleration acting is gravity (g) . And 20m ...
16 views

### Constraint motion [closed]

How can I understand the motion of the various parts of the pulley system?
55 views

### How is the wind pushing the crate left in this exercise, is the force applied is downwards and to the right?

Taken from Fundamentals of Physics. I understand the theory and the resolution. What I don't understand is how what is happening in the diagram is possible. How is it that the wind is pushing ...
67 views

### If A and B are two persons at the end of an ideal rope, where A is applying a force of 70N and B is applying force of 60N then what is the force on A? [duplicate]

So according to me in this situation there are two forces acting on A at the moment, one is the reactive force of 70 N by newton's third law and the other is the force of 60 N exerted by B. Now don't ...
54 views

### How can I calculate the coordinates of segments that form a hanging chain?

I'm trying to get a chain physics model with segments. I'm feeling rather stupid, but how can I calculate which is the new position of each dot when the chain moves its ends? expressed in another ...
34 views

### How are two unequal applied forces at the end of a massless string result in a constant tension throughout? [duplicate]

Even when we apply two different forces $(F_1 > F_2)$ at the ends of an ideal rope, the tension produced in the rope is constant throughout the length of the string rather than being a function of ...
79 views

### Why does the tension in a rope change when the system sets into motion from rest?

Suppose i have held one end of a string and the other end is connected to a block of mass $m$ (say), then if i exert a force of X newtons then the tension generated in the string is also x newtons (...
70 views

### What actually leads to a common tension in an ideal rope even when two unequal forces are applied at the two ends of the rope? [duplicate]

I'm confused with the concept of tension in strings/rope. I have read that tension is an electrostatic force and is created due to the attractive forces by the particles. So I can easily make out that ...
71 views

### Why is an object still moving even if force applied is equal to friction?

Why is an object still moving even if force applied is equal to friction? If this force of friction is the same as the force applied, shouldn't the object be stationary instead?
20 views

### Understanding Newton's third law of motion [duplicate]

If the friction is $14 \; N$, and we apply and we apply 16N on a block, say $A$, then the block applies $16\;N$ on ground and the ground applies $16\;N$ on it. Then how does the block move?
40 views

### What is the physical condition of a loose pendulum string? [closed]

A particle pendulum (thread length $l$) is at rest and is given an initial velocity such as, when the thread "gets loose" / "is not extended fully", the angle is $\frac{2\pi}{3}$ from the vertical ...
55 views

### Given Newton's Third Law, why does it hurt more to be tackled than to tackle someone else? [closed]

In other words, are there more underlying physics concepts occurring in, say, a football tackle? According to Newton's third law, the individual doing the tackling should feel the same force as the ...
71 views

### Spring force in a massless spring [duplicate]

Why is spring force in a massless spring constant throughout the spring? I had a similar question about tension is a massless string. This thread answered it for me. Tension on a massless string ...
51 views

### Kinetics of a Particle: Work and Energy Problem [closed]

I was answering a problem in a book by not following its mass, instead I changed the values of weight A to $115.945$lb and weight B to $95.945$lb respectively. Upon calculating the total energy, it ...
36 views

### Direction of static friction force [closed]

A board lies on top of an uniform cylinders which lie on a fixed plane inclined at angle $\theta$. There is friction in all contact surfaces. If there is no slipping between any of the surfaces, is ...
63 views

### Understanding the concept of energy in a vertical spring system

I have a concept I don't think I get well. I would like to clear out a couple of things. Consider the following system: The spring on the left is the one on the right after extension from equilibrium....
26 views

### Direction of the frictional force

Why is it said that friction always acts in the direction opposite to the relative motion at the point of contact with the surface? When a sphere is rolling down an incline for example, the friction ...
80 views

### The role of friction in rolling without slipping

I am confused about this whole subject. Let's suppose we have a disk standing still upon the ground. Now let's say someone inside the disk shoots a projectile to the left. From momentum conservation ...
48 views

Could anyone explain the case of a ladder leaning on a smooth floor and against a rough wall? It's not clear how there is a vertical frictional force at the wall despite having zero normal reaction ...
53 views

### Origin and Direction of Net Force [closed]

If there are multiple forces acting on an object at different locations on the object with different directions, how would you be able to find the origin and direction of the net force?
27 views

### Is it possible that string's one part has tension and other part does not has any tension?

you have a massless and inextensible string connected to a pulley with some moment of inertia , and if pulley does not slip over string in some setup, IS THAT POSSIBLE TO HAVE TENSION IN ONE SIDE OF ...
54 views

### Confusion about effect of atmospheric pressure on depth at which an object floats [duplicate]

The bottom 3.5cm of a plastic block is submerged in water from the lower end of a spring. Why doesn't atmospheric pressure affect the position of the object? My book says the downward force exerted ...
143 views

### Whether Newton's law is correct? [duplicate]

In my school days, I had been taught that we cannot move a vehicle by applying any force from inside. That is we cannot push the vehicle from inside. But when I was sitting in a scrolling chair, I was ...
48 views

### How to calculate pressure/force on a triangle vertex? [closed]

Assuming those are identical triangles. We add some weights on the upper bar. The only difference is with the location of the weights and the size of the weights. Is there any difference on the ...
80 views

### Work done by static friction in accelerated pure rolling motion [duplicate]

Why is the work done by static friction in accelerated pure rolling motion along an incline actually zero? Somewhere I am grasping the information that work done by static friction is zero as the ...
28 views

### Forces acting while running

If I am running on a surface with friction with no air resistance and also accelerate then net force acting on me is F=ma. The friction acts opposite to direction of motion and is less than the forces ...
35 views

### Centrifugal force vs reactive centrifugal force

After reading (https://en.wikipedia.org/wiki/Reactive_centrifugal_force) (especially third paragraph of the introduction) and comparing it with the answer by Bob Jacobsen posted here (Why does a ...
38 views

### Choosing signs in free body diagrams of subsystems

In an example problem from a book I'm using (David Morin's Introduction to Classical Mechanics with Problems and Solutions), there is a system with a person and a pulley on top of a platform. The ...
14 views

### Why will the balance keep motionless? [duplicate]

A physics problem: A bottle with flies inside it is put on a pan of a balance. When the flies rest on the bottom of the bottle, the beam of the balance is level. If the flies buzz in the middle of ...
53 views

### Ball rolling inside rough cone. In which direction does friction act?

A ball is rolling in horizontal circles inside an inverted rough cone. In which direction does friction act? I believe that for a rolling object on a rough surface, there is no friction in the ...
77 views

### Is there static friction on the box? [closed]

I have the following problem I'm struggling to grasp "A mass of 1 kg is on top of a conveyor belt that moves at a constant 1 m/s. The box isn't sliding. What's the absolute value of the friction? ...
44 views

### Why does the lower rope knot come off as soon as it is pulled, while the upper rope knot gets tighter and tighter?

Why does the lower rope knot come off as soon as it is pulled, while the upper rope knot gets tighter and tighter? The two knots are similar, but one is pulling tighter and tighter, as if it is locked,...
46 views

### Is net force on a geostationary satellite, (when observer is standing just below it on earth) equal to '0'?

Since a geo stationary satellite appears to be at rest form earth, should not the net force acting on the satellite equal to $0$. Now since earth is a non-inertial frame we will have to apply a ...
5k views

### What makes a wheel spin?

I don't fully grasp what makes a wheel much easier to move than to push a solid block. The pressure at the point of contact between a wheel and the ground must be pretty enormous compared to the ...
23 views

### Will the acceleration of a triangular wedge affect relative acceleration of a particle parallel to the inclined plane (the wedges surface)?

I was wondering if the horizontal acceleration of a triangular wedge will effect the acceleration of a particle on the wedges surface (because the wedge is triangular this will be an inclined plane) ...
116 views

### Net Force of Equal and Opposite Gravitational Forces Don't Equal Zero? [duplicate]

I've come across this question, and I'm at at a loss. Two masses, m and M, are in an isolated system. The gravitational forces, F (by M on m) and F (by m on M), are equal and opposite. Why do they ...
41 views

### Help Understanding this Free Body Diagram (Eotvos Experiment)

I am reading through Hartle's "Introduction to Einstein's General Relativity" and it discusses the Eotvos Experiment in Chapter 6. The free-body diagram (shown below) has me a little puzzled. This ...
57 views

### Repulsive and attractive forces causing restoring force in a spring [closed]

So I was recently reading this answer on Stack Exchange, where someone enquired Why is the restoring force directly proportional to extension? Now, the potential energy graph (in the first answer) ...
118 views

### Horizontal acceleration on an inclined plane [closed]

Assume the inclined plane to be fixed. Taking components of gravitational acceleration along and perpendicular to the inclined plane and further taking a component of the component along the plane in ...
28 views

### Problem in statics in applications in engineering mechanics at coursera

in the first image the instructor neglected the reactions at point d and e while he was drawing an fbd to the whole structure ... Shouldn't we give attention to the reactions at d and e while we are ...
30 views

### Balancing a block over two wedges [closed]

This question is from a gre physics practice test. We have two wedges of mass m and a cube of mass M. These are arranged as shown in the figure There is no friction between the cube and the wedges, ...
59 views

### Coefficient of friction between inclined plane and ground

Apply a vertical force to an inclined plane. What coefficient of friction is required between the bottom of the plane and ground to keep the system in equilibrium? Referencing the image, the ...
128 views

### How can action and reaction forces be equal?

Suppose that I push an object having a very small mass of 10 grams. The object accelerates, so does our hand. Since, the mass of the object is less than ours and so is the acceleration then how can ...