# Questions tagged [newtonian-mechanics]

Newtonian mechanics discusses the movement of classical bodies under the influence of forces by applying Newton’s three laws. For more general concepts, use [classical-mechanics]. For Newton’s description of gravity, use [newtonian-gravity].

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### Difference between change in momentum caused by a force and by kinetic energy

I don't see what the difference is between a momentum change caused by a force (eg: someone pushing against a metal ball) and and by transmission of kinetic energy (eg: a metal ball hitting another ...
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### Centripetal force pointing outward

What's going on physicists. I would like some explanation here. I haven't been satisfied with the ones I gathered on the internet. Here is it: If a particle moves in circular motion, there will be a ...
1 vote
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### Conceptual doubt related to motion of two blocks on an incline

I was solving the following question: In the arrangement shown in the figure all surfaces are smooth. Select the correct alternative(s) (A) for any value of θ acceleration of A and B are equal (B) ...
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### Is gravitational potential energy of body by $mgh$ negative? [closed]

Potential energy is found by two formulas: $P.E=mgh$ (in earth, at acceleration g) $P.E=-Gm1m2/r^2 * h \approx -Gm1m2/r$ I am not worried about the approximation of h=r, or use of g in earth, My ...
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### Does A Pivot Exert A Force

On a frictionless horizontal table, a uniform stick is pivoted at its middle, and a ball collides elastically with one end, as shown in Fig. 8.10. During the collision, what are all the quantities ...
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### Why particle is certain to escape the conservative field when the mechanical energy is positive?

It is generally said that the particle is bound into the conservative field when the mechanical energy is negative and zero is the limiting case and the particle will escape the field when the ...
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### Interesting Aerofoil Logical Fallacy

I am new to physics in general having just finished AP Mechanics and have limited knowledge of how fluid dynamics work. But just using forces and a simplified understanding of drag if have come to the ...
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### Person holding two persons hanging over the edge and centre of mass inconsistency

Imagine a person holding the leg of the person in front that also holds the person in front of him. (over the edge like in MI4, assume centre of mass of second person with feet still on the floor is ...
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### Buoyancy basics

I was solving this question and in the solution, they have applied a buoyant force exerted by kerosene. It makes sense by the basic definition of the buoyant force from Archimedes principle. However, ...
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### Why can we treat a ball as a point mass to calculate torque?

A sphere of radius $R$ is supported by a rope attached to a wall as shown in the below figure. The rope makes an angle $\theta$ with respect to the wall. The point where the rope is attached to the ...
1 vote
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### Relative acceleration, mechanics

Consider a system of two objects with mass $M, m$ as presented below. Assume that there's no friction between both the surface, M and between M, m. I'm asked to find the acceleration of m, M using ...
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### Spring potential energy, conversion

I have a physics problem in my book, where a spring is compressed and a ball is laying in the end of the spring. When the spring is released the ball will reach a certain speed. In the solution it ...
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### A paradox while explaining the equilibrium of books

An even number of books (say four) are held in the manner shown in the figure. It is obvious that if we apply a large force inwards, we can increase the normal force, and hence the friction which ...
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### Confusion about sign conventions used in the Doppler formula

Wikipedia gives the Doppler formula as: $f = \left( \frac{c \pm v_r}{c \pm v_s} \right) f_0$ c is the propagation speed of waves in the medium. $v_r$ is the speed of the receiver relative to the ...
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### Work Done by kinetic friction in Circular Motion

We know when an object is moving in a circular motion on a rough horizontal surface, direction of kinetic friction is constantly. Thus, fto calculate the work doen by friction, we need to use ...
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### Tension of rope over frictionless edge obstructing block

Consider the diagram below. All corners are assumed to have no friction. Is it true that the tension throughout the rope is equal in all sections? The section over the edge of the building, the ...
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### Does a rocket moving in a circle expel exhaust at a greater velocity?

Consider a rocket undergoing constant acceleration in a rectilinear path. Assuming the rocket is ideal (ignoring fuel mass and energy loss such as sound, radiation, vibration, etc.) a portion of the ...
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### What is a simple example that contradicts the theory that light (photons) could have a super small mass? [duplicate]

The obvious example is that, to bring something that has mass to the speed $c$ requires infinite energy due to special relativity. But what if a kid asked me "What if light/photos had a super ...
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### Strain energy stored in a bungee cord pulled at its midpoint [closed]

A bungee cord that behaves elastically has an unstressed length $L=.76$ m and a stiffness $k=140$ N/m. The cord is attached to two pegs, distance $b=.38$ m apart, and pulled at its midpoint by a force ...
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### Doppler shift from a moving reflector and source if only the relative velocity is known?

Suppose there is a device which is producing and listening to sound (sonar), a reflector is moving with respect to device and the velocity of reflector and device with respect to the air is not known, ...
1 vote
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### What does it mean when vector quantity is negative?

I’ve seen in some problems that vector quantity is negative. For example, negative Coulomb means that two charges attract… negative acceleration means that object is slowing down. However, magnitude ...
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### Buoyant force on a stick making an angle theta with the vessel

I was solving this question The answer of the question uses balancing of torques. It uses $L=0.5$m I have problem with the fact that they have used buoyant force $F = \rho V g$. Marking the net ...
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### Doubt on conservation of angular momentum for Kepler's laws

Just before proving Kepler's laws, my Professor claimed that if $\vec{F}$ is a central force with center $O$ and it is the only force acting on a point $P$, then the trajectory of $P$ is a curve plane....
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I was wondering about the conditions for an ideal newtons cradle. Under regular circumstances, the collisions are inelastic and a newton's cradle dissipates energy in various forms like heat, friction,...
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### Why is it less shocking to cross the bump with just one wheel? [closed]

Difference between 'go over speed bump with one side' and 'both sides at the same time' I asked a similar question previously and received an excellent answer stating that when going ...
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### Condition for a car moving with a constant velocity [closed]

I seek your help with this simple yet confusing problem. The question says: A car is moving with a constant velocity 10m/s. Which one is correct? No force is acting on the car The force applied by ...
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### When an object is thrown towards the sky it starts to gain potential energy, why?

I didn't think so because when an object is thrown towards the sky it already has kinetic energy and it looses it's energy due to the gravitational force of the earth. When the object looses all of it'...
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### Tendon excursion method application/alternative for joint represented by quaternion in biomechanics

I am building a biomechanical model that consists of spherical joints. I wanted to represent these spherical joints by quaternions. I am struggling to derive how the muscles contribute to the ...
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### Can photons interact with one another? [duplicate]

Photons can interact with matter, particles, nuclei, etc. But can they interact with one another? By interaction I mean any kind of physical interaction: Momentum/Energy transfer, electromagnetic ...
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### Throwing a ball in the air

When we throw a ball in the air, we know that if we do not throw it too high, then g can be held constant over the trajectory and we can approximate the curve by a parabola. However we also know that ...
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### Is it necessary that a force must cause a change in either velocity, shape, or size?

Our physics teacher made us define a force as “A push or pull, which causes at least one of the following- Change in velocity, change in shape, change in size”. If I push a wall really hard such ...
1 vote
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### Can the motion of a rigid body be decomposed into translational and rotational motion about ANY point?

My textbook mentions Chasles' theorem which asserts that " it is always possible to represent an arbitrary displacement of a rigid body by a translation of its center of mass plus a rotation ...
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### What does $v$ actually represent in pulley problems?

Let us consider the problem of two pulleys with boxes attached to their ends. One pulley is movable, and the other is not. The problem requires us to find a relationship between velocities of these ...
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### 3-stage rocket payload problem [closed]

A rocket goes to the sky, and undergoes 3 stages. I want to find the payload of it. In stage 1, 80% of the mass is the fuel, 10% of the mass is dry mass, and 10% is the remaining rocket. Similarly, in ...
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### Local vs distant gravity effects where is the boundary line of effective control? [closed]

I'm not one of the 'gravity is only a theory' crowd or a flat earther that thinks gravity is fake and that down is always down. but thinking about gravity and what has been put forward by many great ...
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### Why do objects in circular motion move outwards instead of inwards? [duplicate]

I know that whenever an object undergoes circular motion then it has a centripetal acceleration towards the centre and a tangential acceleration. Due to these accelerations I had thought that ab ...
I am exploring how the cross sectional area of a drogue chute affects its velocity after travelling a set distance. I got this equation: $$m_1 a = m_2 g - \frac12 c_d \rho A v^2,$$ This covers the ...