Newtonian mechanics covers the discussion of the movement of classical bodies under the influence of forces by making use of Newton’s three laws. For more general discussion of energy, momentum conservation etc., use classical-mechanics, for Newton’s description of gravity, use newtonian-gravity.

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Does moving something horizontally in gravity do no work?

Bill’s job is to lift bags of flour and place them in the back of a truck, which is parked next to him. Sally is loading the same bags of flour into a similar truck that is located 10 m away. ...
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777 views

Force in relation to stationary and non stationary objects

Say you have two situations with an object interacting with the ground. In the first situation the object has been sitting on the ground for a while so the force will be mg. In the second situation ...
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Calculating mass of object by lifting edge

Assuming a solid rectangular plate, hinged along one edge. How does one calculate the mass of the plate if the force necessary to lift the opposite edge is known?
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32 views

Time for two objects to gravitationally attract each other [duplicate]

Possible Duplicate: The Time That 2 Masses Will Collide Due To Newtonian Gravity A student of mine has been working to calculate the amount of time it would take two identical objects, ...
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706 views

Did Galileo offer an explanation why his law of falling bodies is independent of mass?

Naively, (and endorsed by Aristotle) one expects heavier things to fall more quickly, Galileo Galilei showed in fact this is not correct, and that in fact how they fell as independent of mass (if air ...
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Finding Distance an Object Travels Up an Incline After Launch

I've been doing a review for an introductory physics course final. I have a question on one problem though. Here is the problem: A mass (M=2kg) is placed in front of a spring with k=900N/m, ...
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2answers
181 views

Were there any efforts made by early physicists to discover and explain how composite bodies fall?

At the dawn of the modern era, Galileo discovered and described how composite bodies fall through the air (or at least the discovery is usually attributed to him). I'm interested in whether this had ...
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3answers
341 views

The two faces of $F = m*a$

As I have understood, $F(t)=m \cdot a(t)$ can have 2 different meanings: When applying an external force $F$ on a point mass of mass $m$, the resulting acceleration of that mass at time $t$ is ...
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121 views

What is the mechanical explanation for obstruction of motion by an object?

A large box (1) is on a flat surface and is towed by a constant force in the horizontal direction, left to right, but it is not moving due to the presence of a little box (2) in front of the larger ...
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439 views

Would a sneeze by a cosmonaut in a spacesuit affect his movement?

Naive question; feel free to shoot me down It is a truism that any motion in space would continue indefinitely unless it is opposed by an external force. If a cosmonaut were to sneeze within his/her ...
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2answers
315 views

Dynamics - Beginner question

I am trying to understand this question, but I keep coming to a dead end: Two identical rectangular masses rest on top of one another, the top is tied to a wall on the left, while the one on the ...
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4answers
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Why is force described as rate of change of momentum? [closed]

momentum = mass * velocity Differentiating both sides leads to force = mass * acceleration since the mass doesn't participate in the differentiation as it is constant. Is this a sound ...
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Why is there a $\frac 1 2$ in $\frac 1 2 mv^2$?

For elastic collisions of n particles, we know that momentum in the three orthogonal directions are independently conserved:$$ \frac{d}{dt}\sum\limits_i^n m_iv_{ij} =0,\quad j=1,2,3$$ From this, it ...
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1answer
393 views

Dynamics question. Please help, exam coming soon [closed]

I'm trying to solve this elementary problem. I'm studying mathematics, but there is a compulsory course in physics that has to be passed. I'm having an exam in 5 days and I have some doubts on ...
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1answer
135 views

Could a people do all sort of gymnastics movement in vacuum space? [closed]

Could a people do all sort of gymnastics movement in vacuum space? I asked this because I am worry about that the astronaut leave the space shuttle during emergency could not go back to earth by ...
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Will a stone thrown in space move forever?

If I throw a stone on space, in a place where gravity is equal zero, will the stone move forward forever, because no air, so no friction?
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2answers
103 views

We tend to think the action of a constant force…?

This is a school exercise. We tend to think that the action of a constant force produces a constant movement speed as well. How can you explain this situation in accordance with Newton's second law? ...
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In a circular pendulum, where does the equation $v=\sqrt{rg\tan{\alpha}}$ come from? [closed]

In a circular pendulum the $v$ of the particle is $$v=\sqrt{gr\tan{\theta}}$$ where $r$ is the radius and $g$ is the gravity(positive sign), which is equal to ...
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746 views

Question on Impulse-Momentum theory

A 5kg stone kicked by a student undergoes a velocity change from 6m/s to 10m/s in 4 seconds; ---- What is the momentum change of the stone within the time interval? ---- What impulse ...
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115 views

Period of an Object in Periodic Motion

My attempt (if it matters): The initial period is given by $T_X = \frac{2\pi X}{v}$ for some $v$. The new period is given by $T_Y = \frac{2\pi Y}{v}$ for the same $v$. $Y = \frac{X}{2}$, so ...
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3answers
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Conservation of angular momentum for a rigid body rotating about a fixed point

Picture a rigid body such as a sledge hammer. Imagine that the base of the handle is attached to a fixed point such that it can rotate but not translate. I give the hammer a good push to get it ...
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3answers
6k views

Why does a parachute decrease terminal velocity?

Terminal Velocity depends on two things- surface area and speed. These are inversely proportionate. If both these variables affect terminal velocity, why do parachutes slow you down? Initially you ...
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2answers
937 views

How to interpret this vertical circular motion problem?

A bucket of water is tied to a rope and swung in a vertical circle. The distance from the bucket centre to the axis of rotation is $2.08m$. Calculate the angular velocity (in $rad s^{-1}$) of ...
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510 views

Effect of the tail of the cat in the falling cat problem

To explain why a falling cat can turn by 180 degree without external torque and without violation of the conservation of angular momentum, one usually models the cat as two cylinders as in ...
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3answers
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Infinite acceleration?

Why is acceleration regulated by mass? In a frictionless environment, why doesn't an object move at infinite acceleration if force is applied on it? Force causes movement, so unless there is an ...
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734 views

Does the earth's gravity affect horizontal movement?

In a frictionless environment, would the weight of an object affect how hard it is to move it horizontally? Since without friction, there is no horizontal force resisting your applied force, would the ...
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1answer
416 views

What techniques can be used to analyze a rod rotating about the edge of a table?

A uniform rod of length $4x$ is rotating about the edge $O$ of the table. (The rod does not fall off the table.) The centre of mass $G$ of the rod is distance $x$ away from $O$. The rod is making ...
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1answer
362 views

Value and direction of the force applied by a rubberband on an object

Is there a model that would allow me to compute the value and the direction of the force F applied to the object in this case: I have to fixed points: $ A = (-l/2,0) $ and $B=(l/2,0)$. A rubberband of ...
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1answer
864 views

Normal force in a compound pendulum (physical pundulum) system?

Consider a compound pendulum pivoted about a fixed horizontal axis, illustrated by the force diagram on the right: # Okay, I can't figure out where the normal force on the pendlum should point ...
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1answer
110 views

Hurricanes and bathtubs

Why do hurricane winds rotate? I know it´s about Coriolis force but how can I be quantitative? My problem is that I can´t imagine the direction velocity of wind and the angle with earth angular ...
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1answer
225 views

Work Done to click a mouse?

Is there any good research done to find out the work done in clicking a mouse button. any link to that would be greatly appreciated. P.S. i am not too sure whether this question belongs here or ...
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2answers
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Rotational kinetic energy during vertical circular motion of a particle

Why is it not necessary to take into account rotational kinetic energy when using the Law of Conservation of Mechanical Energy to solve vertical circular motion problems? After all, the particle is ...
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410 views

What sustains a rigid body's rotation at its constant angular(rotational) speed?

Continuing from the following scenario from my previous question Centripetal force of a rotating rigid body? : Consider someone pushing a roundabout in a playground. Initially the roundabout is ...
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Centripetal force of a rotating rigid body?

Consider someone pushing a roundabout in a playground. Initially the roundabout is stationary, but when it is pushed, it rotates with increasing rotational speed. The force of the push is ...
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2answers
723 views

What happens when the string slackens during vertical circular motion?

Consider a particle attached to one end of a string of length $l$ moving anti-clockwise in a vertical circle whose centre is $O$. What exactly happens physically when the string becomes slack and ...
2
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2answers
183 views

Knots and strengh of a rope

I read a few times that a knot can reduce the strenght of a rope, but I can't understand why this happens. Can someone explain me what happens to a rope tied with a generic knot and stretched? Is ...
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1answer
246 views

Relationship between the “angle of the floor” and the angular velocity in a banked turn?

Wel, imagine that you're in a carousel, and the floor is, let's say at $\theta=0$ so it's totally horizontal, if $\theta=90$ the floor would be vertically. The object put above the floordoesn't move ...
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1answer
288 views

Bridge Trusses? [closed]

Which kind of truss would produce the best result (aka. best distribution of force): i) An equilateral, isosceles or a scalene triangle ii) 3 small triangles or 2 big triangles (the overall masses of ...
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1answer
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Trajectory of projectile thrown downhill

I'm teaching myself mechanics, and set out to solve a problem determining the optimum angle to throw a projectile when standing on a hill, for maximum range. My answer seems almost plausible, except ...
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2answers
383 views

Explain these graphs of rotation and velocity of pucks on air hockey board

I've been tasked to do a simple experiment on the elasticity of collisions. For this experiment I used two "pucks" (very light circular metal pieces of certain height but hollow) and a table that ...
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4answers
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A person weighing 100 N stands on some bathroom scales in a lift. If the scales show a reading of 110 N, which way is he going [closed]

Can someone answer and explain it please. Here are the options: Moving downwards and decelerating. Moving downwards with a constant velocity. Moving upwards and decelerating. Moving upwards with a ...
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3answers
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How do I calculate DC motor speed for a given load?

Suppose I have a robot of a given mass, and I'm choosing between 2 different wheels and 2 different motors to put on it. For each wheel I have the diameter, and for each motor I know the stall torque ...
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1answer
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Simple Projectile Motion Question

A volcano erupts 50m below the sea level. A rock leaves the crater at 20 m/s at an angle 30 deg with the vertical line. The rock has a mass of 15kg. IGNORE WATER RESISTANCE. It gets out of the water, ...
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5answers
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Why would it be true that people with longer legs walk faster than ones with shorter legs?

When a person walks, the only force acting on him is the force of friction between him and the ground (neglecting air resistance and all). The magnitude of acceleration due to this force is ...
3
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1answer
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Center of Gravity vs Center of Mass

To calculate the center of gravity of a distribution of mass, can I use gravitational potential (scalar) or must I use gravitational field (vector)? And why, generally, the center of gravity goes ...
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1answer
153 views

How much time will a pendulum lose in one day?

A pendulum clock beats every time the bob passes through its lowest point. What must be the length of the pendulum at a place where g= 32.0 ft/s^2? If the clock is moved to a point where g=31.0 ...
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519 views

Is it circular reasoning to derive Newton's laws from action minimization?

Usually, a typical example of the use of the action principle that I've read a lot is the derivation of Newton's equation (generalized to coordinate $q(t)$). However, in the classical mechanics ...
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303 views

Bee in a vehicle [duplicate]

Possible Duplicate: Speed of a fly inside a car Just a conceptual question: If a flying bee is inside a speeding vehicle, will it have to "fly" just as fast as the vehicle to stay aloft ...
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6answers
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Is the energy conserved in a moving frame of reference?

Consider this situation: When the box is at the bottom of the frictionless incline, it will have a velocity of $v_f$. The person is an inertial frame of reference that moves at a constant ...
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1answer
741 views

Calculating semi-major axis of binary stars from velocity, position and mass [closed]

I'm trying to calculate the 'instantaneous' semi-major axis of a binary system with two equal (known) mass stars for an $N$-body simulation. I know their velocities and positions at a given time, but ...