# 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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### Classic man on boat problem

A man is standing on one side of a boat and the boat is stationary. We ignore friction between water and boat (and air friction). Thus there are no external forces on the man+boat system. So ...
661 views

### How is weight distributed in a stack of boxes? [duplicate]

Consider the following stacks of 2D boxes with uniform density: ...
318 views

### Reduced-gravity flight (A300 0-G): what is actually reduced?

I doubt I can hide from the effects of gravity when I'm close to Earth. We usually don't question this biker is fully experimenting gravity: Source. But with the well-known "reduced gravity" ...
2k views

### What is the direction of friction on both tyres of a cycle? [closed]

What should be the direction of friction acting on both tyres of a running bicycle? My friend said that the direction of friction will be opposite for both tyres. My view is different, I think the ...
306 views

### How do I analyse this pulley-trolley system? [closed]

"find a force F such that the blocks are stationary relative to the trolley. All surfaces, wheels and pulley are assumed to be friction-less" 1: This is a very common mechanics problem and ...
116 views

### Why is the Normal force in the picture not perpendicular to the surface?

My teacher said that the first is true, but the normal force should be perpendicular to the surface?
288 views

### Conceptual doubt in Tension force

I recently studied that Tension in a string is a kind of force originated from electrostatic attraction between the atoms of the string in which the force is originating. My doubt was that: Assume ...
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### How can I use Newton's laws of motion to determine the force acting on the rope? [closed]

Imagine there is a painter, weighing $180~\rm lb$, that is working from a bosun's chair hung down the side of a tall building. Suppose that he pulls down on a fall rope with such a force that he ...
329 views

### Confusion about force analysis in 3D space

A book I'm using states that it is possible for a system of forces to produce a net translational force with no turning moment if the line of action of the net force does not pass through the origin ...
121 views

### Do we all actually just weigh half of what our bathroom scales tell us?

Here's the reasoning: Newton's third law tells us that every force has an equal but opposite reaction force. So besides my weight pushing down on the scale from above, there's also an equal force ...
900 views

### Conditions for the tension to vary in the rope

What are the conditions for the tension to vary in the rope. I have read below conditions 1. rope has to have some mass 2. rope is accelerating I get the 1st one,...
167 views

### Work done by friction in this Case

So there is an elevator going down with a constant and the block does not slip on the wedge. We have to find the work done by friction in time t. So the answer given is $-mgvt\sin^2\theta$. What I ...
479 views

### Force Diagram on an Overhanging Book [closed]

I am a beginning physics student. I have a question (probably very simple for you all haha) about forces on an overhanging book, off a table. We all know that the max you can push it would be half ...
285 views

### Inverted pendulum, EOM

Consider the inverted pendulum shown below: where $F$ is an external force, $B$ is the CoM of the rod, $A$ is the position of the joint where the rod attaches to the car. Angles increase in the ...
38 views

### Buoyant force on partially submerged bodies

When a cylinder placed on a fluid,it is partially submerged and attains equilibrium at that state. In equilibrium $$F_B=mg$$ Where $F_B$ is buoyant force and $mg$ is weight of the cylinder. But we ...
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### How do we define what is "External" force or "Internal" force in the context of momentum conservation?

I know that without presence of any "External" force momentum is always conserved. But how do we distinguish between "External" force and "Internal" force where all are "Force"?
812 views

### Zero gravity - how it is possible?

If planets in the solar system are under the influence of gravity, how does one achieve zero gravity just outside Earth? (Please correct the question if the terms are wrong, but I hope the question is ...
29k views

### Why is the tension between two masses connected by a rope and undergoing a force along the direction of the rope less than that force?

Two different known masses at rest on a frictionless surface are connected by a rope. A known force F is applied horizontally to mass 2 so that the boxes begin to accelerate in that direction. The ...
3k views

### Why am I not accelerated by the reaction force applied by Earth on me? [duplicate]

Newton's third law says that "to every action, there is always an equal but opposite reaction". And Newton's second law of motion says that, $F=ma$ $=>$ $a=\frac{F}{m}$. People says that If I stand ...
88 views

### Why is this $T_2=2\times T_1$?

I have a doubt, I want to understand how this works. Why is the formula like this? Hope you can help me, sorry for my bad English.
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### Is my free diagram of a spring stretched on one end and attached to the wall on the other end correct? [closed]

Consider the following figures. The top one shows the construction of a spring where its left end is attached to the wall and its right end is stretched by a force. The bottom one is supposed to be ...
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### In a system of stacked blocks with friction, how can the top block have no acceleration?

Suppose I have a block of mass $m$ on top of a block of mass $M$. Friction exists between them. I apply a force $F$ on the top block. The equations of motion are thus $$F-f_{frictional}=ma$$ f_{...
174 views

### Series Combination of Spring

I'm a little confused with this high-school mechanics question. Where you have two spring with different spring constants, say $k_1$ and $k_2$, we joint them together and of the resultant spring, one ...
481 views

### A simple pendulum

The idealized simple pendulum model (see the following figure) assumes that at every point of time the string to which the bob is attached exerts an equal and opposite force on the bob as does the ...
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### Conservation of momentum in a newton’s cradle with inelastic collisions

Let's consider that we have a Newton's cradle in vacuum: Considering that each ball has a mass of 100g or 0.1 kg we release the ball and at the time of contact, the ball has a final velocity of 1 m/s....
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### How is a running man able to Accelerate himself?

Suppose a man is running and he gradually speeds himself up . For this he applies a force on the ground backward and the ground pushes him forward . This is probably due to to friction between the ...
44 views

### Tension due to unequal forces on a massless spring [duplicate]

When a massless spring is pulled by 5N on both sides the tension in the spring is 5N (proved by considering COM at rest and breaking the spring into two springs of 2k each)...what if the forces ...
271 views

### Isn't friction on an incline coefficient of friction times the Reactional force?

Question - "As shown in figure a body of mass 1 kg is shifted from A to D on inclined planes by applying a force slowly such that the block is always in contact with the plane surfaces. ...
300 views

### How is power of engine transferred to kinetic energy of car?

Okay, I understand that via the torque from the engine, the wheels push back on the ground, and static friction pushes forward, thus accelerating the car. However, the force of static friction does ...
98 views

### Why do riders feel forced down into their seats at the bottom of the first drop on a rollercoaster?

I am trying to figure out what forces an $80.0kg$ rider travelling at $110.0km/h$ ($30.56m/s$) would experience when at the bottom of the first drop on a rollercoaster where the radius of the ...
2k views

### Vertical circular motion: minimum velocity

In vertical circular motion while finding the minimum velocity at the bottom-most point for looping the loop, why do we take the tension at the topmost point to be zero?
18 views

### Pascal's Law related

Which is more valid for The pressure intensity at a point in a fluid is the same in all directions, only when: The fluid has zero viscosity and is at rest? or There is no motion of one fluid layer ...
33 views

### Cyclist leaning when rounding a bend [duplicate]

Why? Now here's the question that got me pondering A cyclist rounds a bend, The surface of the road is horizontal. The cyclist is forced to lean at an angle of $20^\circ$ to the vertical to 'only ...
280 views

### Why does frictional force cause a car to move? Also, is friction a reaction force? [duplicate]

My teacher told me that this was because frictional force resists relative motion between the engine and the car. However, in this case it seems to allow relative motion between the ground and the car....
121 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 ...
446 views

### Tension in Common Catenary

I was reading the intrinsic equation of common catenary , where the author assumes tension in the catenary and proceeds. Why does a freely hanging rope with uniform mass per unit length has tension ? ...
192 views

### Newton's $1$st law question

A long time since I posted it, still did not get a satisfactory solution. So I restate the problem - Why does not an object attached to a string which is attached to the roof of an accelerating bus ...
674 views

### I have some trouble with springs in series [duplicate]

I am starting with problems of combined strings. I think the basic ones are strings in parallel and in series. For me it´s easy to understand the formula for the parallel but don´t understand how the ...
2k views

### Why force applied which is equal to weight of an object is able to lift the object? [duplicate]

Suppose there is an object of weight 'mg'. If we apply a force equal to mg, why the object is lifted up as its weight and the force applied are equal and opposite in direction should be cancelled out ...
56 views

### Why do I get inconsistent equations when I resolve forces vertically and perpendicular to the plane? [closed]

Consider a body of mass $m$ kg on a smooth inclined plane inclined at an angle of $\theta$ to the horizontal. Let $R$ be the magnitude of the normal reaction force acting on the body. If I resolve ...
574 views

### Physical meaning of same pressure on the same plan (hydrostatic paradox) with different weight above them [duplicate]

In this picture the points on red have the same pressure because the weight of the fluid is the same above them. But according to pascal law the point on black must have the same pressure(both 3 ...
We are in an isolated system consisting of a large massive smooth sphere/planetoid with radius $R$ and due to its mass an nearly constant acceleration $g$ exists in its vicinity. A small particle is ...