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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Newton's third law cancelling

I have recently been doing some work around Newtons third law. And I was thinking about a question revolving around the topic. It is a common question of how can we move at all if all forces are equal ...
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Is the system of parallel springs always have a same extensions?

In a normal system of parallel springs, We say that their extension of the each spring is same, so the equivalent spring constant k is the sum of all k of spring. But how can this make sense if one ...
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What forces act on an element taken in a body which is subjected to no external forces?

Consider a block (rigid) which is lying on a table. If we take a differential element in the block and try to draw its Free-body diagram, will there be any forces other than gravitational force acting ...
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Conservation of energy in a rigid body

"One end of a rod of uniform density is attached to the ceiling in such a way that the rod can swing about freely with no resistance. The other end of the rod is held still so that it touches the ...
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Elemental problem of dynamics

Ok, let's go fast. If we have the following system, and we want it to be static (acceleration = 0), we will always and obligatorily need friction, or any other force to oppose those existing in the ...
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Friction when a car is moving in a circle

When a car is moving in a circle, I want to know how the friction of the car could be drawn. I have found the following picture. But I know that the friction force is always in opposite direction of ...
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How to I make a free body diagram of a machine with slanting beams in it? [closed]

In my school class I had to design a product. While drawing the free body diagram I didn't know where to begin. The sketch of the product is: Can someone explain to me how I am supposed to draw the ...
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Force required to move a liquid through a specified opening

If I know the rate of a liquid, the density of that liquid, the velocity of the liquid, and the size of the opening. How would I calculate the force required (in PSI) to move that liquid through the ...
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What rotates a disk hung at center of mass when it is tilted?

when a disk is hung by a string attached to the center of mass point is tilted, what is making it fall and become horizontal again Note the white line is a light string. Here $Torque_{net} = 0$ and $...
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Free-body-diagram of a falling ball

The free-body-diagram of a falling ball where air resistance is not negligible, is the drag force ever greater than the weight of the ball? I mean mustn't it as it is slowing down? But then how is the ...
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Simple forces diagram of a car maintaining speed up a slope

I'm currently in training to be a high school science teacher in Australia and I'm looking at my year 7 class's test for this term. I think the answer to one of the questions on the answer sheet is ...
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Tension in thread

We know a thread or string experiences the same tension force throughout the whole length,but when we tie a knot in the thread,why does the tension force become different in the two sides of the knot? ...
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How is the weight of a hanging block communicated to a scale?

I read in a physics text (Tipler, Physics for Scientists and Engineers, 5th ed.) that if we have a scale, and on the scale is a hollow box of mass $M$, and inside the box is a block of mass m hanging ...
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Truss Deflection Problem

Dear Readers, why doesnt the deflection formula depend on moment of inertia (I) or even the second momnet of area that are responsible for the cross-sectional shape of beam. Does that mean in the ...
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What is meant by unbalanced force? [closed]

If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no change in motion. If they are not equal and opposite, then the forces are unbalanced and ...
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Can tension change in a massless string if there are three forces acting on it?

Consider this massless string, which has three forces acting on it, two on the ends and one at the middle: Would the tension change at the midpoint where the $5 \text{N}$ force is applied? I think it ...
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What does it really mean to have infinite tension?

Let an object of mass $m$ lie on a wire. The wire is much smaller in mass than the object and so its mass can be negligible. As the object lies on the wire, the wire is pulled down to a position where ...
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Confusion about tension and disk

Why are the two tensions not equal? I thought tensions on two ends of a cord are always equal. And are the motion of the disk caused by friction force due to the motion of the cord and disk surfaces?
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How to find accelerations/tensions here? [duplicate]

$m_{2} = 6 m$, $m_{1} = m$, $m_{3} = 3 m$ I used conservation of string length and got $a_{3} + a_{pulley} + a_{1} = a_{2}$ and $T_{1} = 2 T_{2}$, but I have a feeling it's wrong because if the pulley ...
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We know that action reaction pair don't get cancelled as they act on different objects. But, can the resloved components cancel each other?

I am not able to understand the FBD given above. Here is my understanding: According to Newton's 3ed law, If apply the force with the help of my legs to the ground, the ground pushes me back with an ...
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Fan in a sealed box

Let's say that there is a helium balloon attached to a large, sealed box. The box is off the ground and there is neutral buoyancy. The box + balloon are simply floating in air, not moving. Inside the ...
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Can an external force act on a single body in a system?

Say I have a very simple example of a train, or a pulley system, or one block pulling another before they both fall of a table, so two bodies connected by a very simple mass-less cable or string. A ...
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Need help confirming answers; Laws of Motion Problem

I just recently started reviewing my old textbooks for fun (don't judge), and I'm having trouble wrapping my head around tension forces in this review question for the Laws of Motion chapter. Before ...
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A paradox to law of conservation of angular momentum

I came across the following problem: A small body of mass $M$ tied to a non stretchable string moves over a smooth horizontal plane. The other end is being drawn into a hole with constant speed. Find ...
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How to find the acceleration without the generalised coordinates?

I am currently reading through this website on the generalised coordinates. Regarding the first example, I have no troubles understanding the generalised coordinates approach, but I cannot solve the ...
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How does the net vertical force equation for a non-relativistic string derived?

In the following image from "A first course in string theory", we get the net vertical force of a string, dFv. While I understand the first equation, I don't understand how the second ...
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I am not able to understand the free body diagram for the bottom figure

PS: This is taken from:https://en.wikipedia.org/wiki/Fictitious_force I am not able to understand the free body diagram for the non-inertial frame of reference.It would be of great help if someone ...
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How does the work done by a cord-over-a-pulley work? [closed]

I can use the integral of power with respect to time to solve problem. In this situation, what is the work done on the cart by the tension? Please do not use calculus.
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When are pseudo forces considered to do work?

I was solving a question in which: there is an inclined wedge with a smaller block on the inclined side of it (all surfaces are smooth). The wedge is then given an acceleration by application of an ...
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2 answers
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Object moving down an inclined plane and an object moving along a banked road [duplicate]

Why is the normal force of an object sliding down an inclined plane equal to mgcos(θ), whereas for an object moving along a banked road, the normal force of the object is mg/cos(θ)? Also, in some ...
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What is the constraint acceleration equation of the system? [closed]

In the question there is a hint given, $y_A$ is not constant. From this hint I began to look at the pulley that holds $m_1$ and $m_2$, and can see that it has the same tension as $m_3$. From this ...
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How do objects slide under one another?

I am making a small Robot to pick up things off the ground, and I am trying to understand the physics behind objects sliding under one another. The exact scenario that I am talking about in real life ...
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Why is the acceleration of $m_2$ downward?

The magnitude of the acceleration of $m_2$ is $a$. It does not say in the question whether it is downward or upward. But the answer assumes it is downward. So I think either it is badly framed, or it ...
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Free massless spring pulled from one end

When two masses are attached to the ends of a spring and a force is applied on one of the masses, each point on the spring will move the same distance from its equilibrium position. This is also the ...
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Static mechanics: I get two different forces in an equilibrium system [closed]

The problem comes from "Engineering Mechanics Statics Dynamics" by Russell Charles(newest edition), on page 97, f3-4. You can see it here: https://www.youtube.com/watch?v=Nw7iN4BnU44 The $x ...
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How does a gravity defying stand comes in equilibrium?

The gravity defying wine bottle stand are now becoming very common these days. Can someone explain in detail the physics involved here? Here is a video that gives details about its making.
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Minimum force required to push a car up a slope [closed]

I have a problem calculating the force required to push my car up an inclined road. My car has 1200 kg mass, the road angle is 4 degrees (7 percent slope) and static coefficient of friction between ...
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4 answers
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How to understand what causes the centripetal force in this situation and what would be the direction of those forces and the centripetal acceleration [closed]

A table with smooth horizontal surface is turning at an angular speed $ω$ about its axis. A groove is made on the surface along the radius and a particle is gently placed at a distance $a$ from the ...
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3 answers
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Why does weight increase if an object is held in water?

If you put a glass of water on a scale and partially submerge an object in it while still holding the object in hand, the scale readout shows an increase in mass. It happens if the density of the ...
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Specialising Archimedes' principle

I have a problem with Archimedes' principle. Suppose 'A' is a object with a density of 'd'. So A will immerse in a liquid that has a lower density than d. But when it touches a single molecule of that ...
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When the tensile force is equal to the weight of the body

I have met a lot of problems where the tensile force is different from $mg$, while in this one problem in the solutions it is written only that the tensile force is equal to mg. So if someone has time ...
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2 votes
2 answers
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How does Newton's Third Law hold in cases of net force? [duplicate]

In a case where there is a net force, how does Newton's Third Law hold? For example, if I give a book a push and it starts to slide across the table, that means it was not able to neutralize the force ...
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2 votes
2 answers
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Why is total work 0 on U ramp?

Suppose there is a U shaped frictionless skateboard ramp. If I put on far top left of the ramp and then release it until it reaches top left then from $\Delta K= W_{tot}=0$ because initial and final ...
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Does Newton's third law hold only for isolated system?

I'm trying to show the equivalence between the conservation of momentum and the Third Newton's Law. We have the Newton's third law, that asserts that if object 1 exerts a force $F_{21}$ on object 2, ...
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How to find a condition for direction of motion in a system with hanging pulley? [closed]

I'm trying to wrap my head around the following system once it is released from rest. We assume that: the masses of the two fixed pulleys attached to the ceiling are negligible the mass of the rope ...
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Why does a motorcycle turns when it is leaning?

I have been some discussion about this topic but everytime people ends talking about counter steering and leaning in order to compensate for the centripetal force and don't fall, but those are not my ...
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Why do we feel weightless while free fall but not while hanging with a string?

So why do we feel weighted by hanging on a string as their is no normal force acting on the object only tension force on the string not on object
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Weight on a scale

imagine that you're at the baggage weigh in point at an airport. your luggage is on the scale and you try to cheat the price by pivoting your heel on the ground and toe beneath one end of the suitcase ...
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Why are the net forces in this FBD $mg\sin \theta$?

Question: It says the sum of the net forces is $mg\sin\theta$. I have tried drawing the angle in two ways: and both cases i get that net forces $=mg\sin\theta$ What am I doing wrong?
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1 vote
2 answers
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What is the acceleration of a ramp on a table when a body slides on it? [closed]

I found an Olympiad problem: Find the acceleration of a ramp on a table when a body slides on it. Assume there is no friction between the body and the ramp, and between the ramp and the table. I ...
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