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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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Equilibrium of forces acting on a lifted car

Assuming there is a car that lifted by a tow cable such that only the rear wheels are in contact with the ground, how does the tension in the tow cable, the weight of the car and the contact forces ...
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A 25-kg box is pulled to the right on a rough, horizontal surface with a rope that makes an angle of 40 [closed]

(a) Draw a good FBD for the box. (b) What is the apparent weight of the box? (c) What is the magnitude of the friction force acting on the box? (d) What is the acceleration of the box?
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Pressure at a point in a fluid [duplicate]

We know that to maintain horizontal equilibrium of fluid particle horizontal forces should balance and similar for vertical , but why is the horizontal pressure at a point equal to vertical pressure?
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What force causes tangential acceleration? [closed]

I believe the static friction is responsible for the centripetal acceleration whereas kinetic friction is responsible for the tangential acceleration. But the answer key states otherwise and says it's ...
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If an object would be too tough to puncture while static, is it possible to pierce it while holding still and having it move toward you?

In The Lord of the Rings it is claimed that no man has the strength to pierce the skin of the giant spider Shelob. In a dramatic turn of events, Shelob lunges at Sam with such force that she pierces ...
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2answers
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Why do we include $x$ in this Spring Equation?

I am currently in Physics 1 and we are learning about Energy. This may sound like a dumb question but I am currently trying to understand this. Here is the question of the problem: A 10kg block is ...
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3answers
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Attack point of buoyancy force

I have seen free body diagrams of submerged objects that show the buoyancy force acting on the centre of mass of the object. However, the buoyancy force arises due to pressure differences between the ...
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1answer
28 views

Why is the tension in a pendulum string highest when it is at the mean position?

Why does the string of a pendulum have max tension when it is at the mean position?
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A confusion with Archimedes' principle [duplicate]

Consider a perfectly cuboidal block floating on a liquid contained by a beaker of smooth horizontal bottom surface. The density of the liquid is more than that of the block. Now, an external force ...
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2answers
55 views

Why aren't we pushed one left/right direction when we stand closer to one side of a pool?

Why isn't it that we are pushed more one direction left or right than the other if we aren't standing in the middle of the pool/ any fluid? By pressure=mass(height)(gravitational constant) and ...
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4answers
56 views

Springs and Hooke's Law

Suppose a mass was stretching a vertical spring. Why does the mass have a velocity in its equilibrium position where the net force is 0? Note the spring is massless.
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The effect of fixed pulleys on weight at 90 degrees

If you have a fixed point pulley, and you are pulling a rope attached to a 100kg weight, how much weight are you pulling at a 90 degree angle? ...
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2answers
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How is it possible to survive more than a few cm submerged underwater?

Suppose you hold your breath and dive a meter underwater. Assuming the surface area of the back of your body is approximately $1$ m$^2$, you have about $1$ tonne of weight above you. If you were out ...
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Confusion about conservation of linear momentum in a bike

A bike is moving with some velocity.There is some frictional force between the wheels of bike and ground.Now you apply brakes and the bike stops after some time.Brakes apply a force say F on wheels ...
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2answers
52 views

Newton's third law in a two body system

If I push on a table with some force 'f' then by newtons third law of motion the table also applies the same magnitude of force on me in the opposite direction. I get that there may be various forces ...
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1answer
23 views

Why does the vector in the banked turn problem not point to the center?

I am currently working on the banked turn problem. I know that once you set up all the equations properly you end up with $$v^2=gR\tan{\theta}$$ I drew a little diagramm of the forces: I know that ...
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9answers
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Why do bikes hardly ever skid while braking with the front wheel?

When abruptly braking with the rear wheel on a bike, it tends to skid pretty easily. Doing the same with the front wheel is a very different experience. Instead of skidding, the bike lifts the rear ...
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Tension in a rope pulled equally on both sides [duplicate]

I would really appreciate it if someone can help me understand Newton's third law as it applies to the tension in a rope involved in a game of tug-of-war with 0 acceleration. Disregarding friction, ...
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1answer
72 views

Violation of law of conservation of linear momentum

A bike is moving with some velocity.There is some frictional force between the wheels of bike and ground.Now you apply brakes and the bike stops after some time.Brakes apply a force say F on wheels ...
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1answer
55 views

How do I calculate the maximum force needed to apply on the structure for it to topple over? [closed]

The structure consists of 6 parts as shown and the purpose of this structure is to be placed in construction sites to monitor the progress of works. As such, the structure will be subjected to ...
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2answers
45 views

Reason of no reaction force on a person in a lift falling freely under gravity

a person in a lift falling freely under gravity feels weightlessness because the force of reaction between the person and the plane with which he is in contact vanishes. why force of reaction vanishes?...
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2answers
45 views

Power by normal force

Would the power created by the normal force always be zero? Since normal force is always perpendicular to the object?
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0answers
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Why don't I accelerate upwards due to reaction force? [duplicate]

Now I am standing on the ground and thinking that I exert a force equal to my weight on the ground. So as a reaction the ground also exerts a equal reaction force on me of the same magnitude and ...
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12answers
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If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards? [closed]

If gravity disappeared, would Newton's third law make everything that was pressed to the ground by gravity get pushed upwards?
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2answers
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Can the motion of an object in the absence of external forces be different than that of an object with zero net force?

The book says that: Newton’s first law does not say what happens for an object with zero net force, that is, multiple forces that cancel; it says what happens in the absence of external ...
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4answers
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Conceptual help with a modified atwood machine

From my understanding, in this atwood machine, one mass is on a horizontal surface, and the other is hung off a pulley and left to freefall. Pictured below: If only the hanging mass affects the ...
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3answers
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Tension in a stone, string system undergoing uniform circular motion [duplicate]

I've recently read that a string can be assumed to be a spring with a really high spring constant, and it applies a force in the opposite direction to the force being applied Like in this case, ...
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1answer
42 views

Why does bike trip on the opposite side when turning the handle?

It can be observed on a stationary bike and also on a moving bike that on giving a jerk on the handle the bike leans to the opposite direction in which the jerk is given. Is it due to angular momentum,...
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3answers
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Very elementary question about Newton's third law

A boy presses his palms against the palms of another girl on an ice rink. They exert an equal force on each other and move in opposite directions. This may seem quite silly but what about a large ...
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2answers
58 views

Why do we steer in the opposite direction while countersteering?

I know the theory behind bending inward while taking a turn. It is done to make a component of friction act as centripetal force and prevent from us from getting thrown out due to centrifugal force. ...
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2answers
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Centripetal force and vertical motion

In regards to an object in vertical circular motion - such as a motorcycle going around a circular track, am I correct in saying that $F_\text{centripetal} \neq F_\text{net}$ ? Generally in school, we ...
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1answer
67 views

Movement of a helium filled vs lower-density-gas filled balloon inside an accelerated car

It's well known that a helium balloon inside of a car moves forward when the car accelerates, and backward when it slows down. What would happen, though, if a lower density gas was used instead of ...
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2answers
28 views

Scale readings, the definition of weight, and projectiles

For this question I would like to define weight as a scale reading. I have a conceptual question: if I leap off a scale, according to my definition of weight the scale will claim I am heavier than ...
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1answer
47 views

Banking of road

If a car is moving on a banked frictionless road one of the component of normal reaction force acts as the centripetal force required for the turn. But normal reaction force is a reaction force. ...
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4answers
67 views

Wood in water and buoyant force

Wood doesn't sink in water because its density is less than water density. So $ΣF=0$. But what is the force that counterbalances the gravitational force if the wood does not sink in water so that ...
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1answer
78 views

Tension of String Connecting Two Objects [closed]

I believe the way you find tension in a string connecting 2 objects is by using Newton's Second Law on the object which the tension points to. But I am not completely sure how you would find the ...
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1answer
101 views

Force required to move bar at one end

A uniform bar of length $L$ and weight $W$ rests on a level floor so that there is a uniform contact pressure between floor and bar. A horizontal force $P$ is applied at one end, normal to the bar. If ...
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4answers
71 views

Applying Newton's Laws in a Circular Motion

A child ties a rock to a rope and turns it around describing a circle. horizontal. My Classical Physics teacher has told me that the string cannot be perfectly horizontal, but I don't know why. I ...
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1answer
54 views

Proof of the Law of the Lever

Is there an accepted proof of the Law of the Lever? I know of several attempted proofs, such as Archimedes's, but these either are incomplete or do not transfer to the setting of Newton's Laws. (It ...
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1answer
57 views

$mg\cos\theta=N$ or $N\cos\theta=mg$ [duplicate]

I was reading up of centripetal motion when I saw the relation that $mg=N\cos\theta$, as can be seen from http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/carbank.html, in the case of a ...
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1answer
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How does Newton's third law work in springs?

So in high school I thought 'if Newton's third law works, why do springs ever move?' In other words, if I pull on a spring, that means a force of the same magnitude is being exerted in the opposite ...
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1answer
65 views

Is friction affected by gravity?

Some people said that moving a car on the moon would make the tires spin a bit more compared to Earth's. But then I started thinking that if static friction and gravity are perpendicular to each other,...
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1answer
63 views

Resolving forces on inclined circular motion

When resolving forces vertically and horizontally in a problem where a car is going around a banked bend, why do you consider the components of the normal force? Shouldn’t the normal force just cancel ...
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3answers
39 views

Forces in a staically determinate cantilever Truss, why some experiences compression while others experience tension?

The Redundant Truss Apparatus is constructed with units of basic triangular pin-jointed. At joint 1, it is fixed firmly due to a support. At joint 2, it is fixed to a movable support. Suppose at ...
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1answer
74 views

$μ = \tan\theta$ - Why? It makes sense mathematically, but if it's based on the materials how does that work?

We were presented with a problem in physics today in which we calculated that the coefficient of static friction is equal to the tangent of an angle This is on a ramp using the laws of friction. My ...
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1answer
453 views

Friction between two blocks on top of each other

I am a little bit confused to the concept of friction between two blocks on top of each other. there could be two situations: the first situation is when all surfaces are frictionless including that ...
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4answers
56 views

Newton’s Third Law Intuition Example Question and Clarification

Assume that I was in space, where there is no friction. Also assume that there were two objects at rest: myself and a matchbox. Does this mean that, by Newton’s Third Law, since there is no friction, ...
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4answers
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Does $m$ in this problem refer to the total mass of the system or just the mass of a single body?

I am trying to figure something out in this problem: I am having trouble with these types of problems because often I don't understand which forces I need to consider when setting up $F=ma$. Here is ...
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1answer
41 views

Connected system

two bodies having masses M1 and m2 (M1>m2) are attached to the ends of a light inextensible stringpassing over a smooth frictionless pulley.when the system is released M1 moves downward and m2 move ...
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1answer
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Normal force in uniform circular motion [duplicate]

When we consider a person on a ferris wheel, the forces acting on him at the top are the normal force and gravity. The acceleration of the person is downward (towards the center), so by Newton's ...