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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943 views

Dynamics of counter-rotating flywheels

I've wondered about this for ages. If we create a pair of flywheels that rotate in the opposite direction with the same angular momentum, but are co-located and have the same mass and inertial moment ...
7
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3answers
561 views

Energy needed for Superman to take off and fly at the speed of sound

I just watched "Man of Steel", and I'm wondering if my logic is correct. Let's assume Superman is 80 kg. The energy required to take off from the rest to reach the speed of sound in air (if I neglect ...
0
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1answer
82 views

Calculate orbit height from tangential velocity

Is it possible to calculate the altitude of a satellite orbiting a planet, just from the planet's mass and the satellite's velocity, assuming that the satellite is in a perfect circular orbit? If so, ...
4
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2answers
5k views

How can an object's instantaneous speed be zero and it's instantaneous acceleration be nonzero?

I'm studying for my upcoming physics course and ran across this concept - I'd love an explanation.
1
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1answer
45 views

Newtonian tidal forces and curvature

Today in my physics class, my lecturer said something which confused me. He said: "Newtonian tidal forces are reinterpreted as a manifestation of curvature in General Relativity". Now I know what ...
17
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3answers
5k views

Why doesn't the speed of Earth (moving through space) kill us?

I have read different speeds of Earth in different sources. $382\;{\rm km}/{\rm s}$, $12\;{\rm m}/{\rm s}$ and even $108,000\;{\rm km}/{\rm h}$. Basically, it's moving too fast around the Sun. And the ...
3
votes
5answers
161 views

High speed does not kill. Does acceleration do it ? or jerk?

In a recent question the OP asked why high speed will not kill us. The accepted answer, highly upvoted, stated very first that Speed doesn't kill us, but acceleration does. The second answer ...
0
votes
3answers
133 views

Force vs. impulse: what is the math description of their interaction?

Suppose the box (stone, bullet..., $m =1$) is not moving upward because of a lift, but has been shot and has $p = 20 kgm/s, v = 20m/s, KE = 200 J$ Gravity is doing negative work and subtracting ...
0
votes
1answer
52 views

Calculating the acceleration in a multiple pulley system with one mass? [closed]

This sounded really simple to me at first, but how would you calculate acceleration within a multiple pulley system like this one . I understand that $5T = mg \implies T = \frac{mg}{5}$, but what if ...
0
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0answers
26 views

Calculating forward velocity of theoretical force against a wedge

Full disclosure: Writer here, not mathematically inclined at all. However if it's explained to me like I'm five, I'm confident I can plug this into a spreadsheet (hopefully) for future use. There's a ...
14
votes
3answers
372 views

Underdetermined forces in a statics problem

I was trying to cook up a good exam problem on Newtonian mechanics, and I came up with one that I didn't fully understand myself. Always fun when you can outsmart yourself. In the figure a cylinder ...
0
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3answers
104 views

Why doesn't any object that doesn't have direct contact in a fast moving vehicle feel G-force or slam behind or ahead when braked or accelerated?

Why doesn't any object that doesn't have direct contact in a fast moving vehicle feel G-force or slam behind or ahead when braked or accelerated? For example when we are in a car (even with all ...
0
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0answers
36 views

Torque, angular velocity, keeping track of the rotation of a sphere

I'm trying to simulate a rotating sphere due to a torque on a specific point on the sphere. Say the sphere is connected to a string (so variable length) on the bottom, on $(r, \theta, ...
0
votes
2answers
1k views

Relative Velocity and Momentum

The question is, A $45.5~kg$ girl is standing on a $140~kg$ plank. Both originally at rest on a frozen lake that constitutes a friction-less, flat surface. The girl begins to walk along the plank ...
30
votes
5answers
5k views

Which ball touches the ground first?

This is a very well known problem, but I can't find an answer in the specific case I'm looking for. Let's consider two balls : Ball 1 weighs 10 kg Ball 2 weighs 1 kg Balls have identical volumes ...
0
votes
1answer
69 views

Difference in mass shown on balance and real mass

Milk of density 1000 ${kgm}^{-3}$ is poured at a steady rate of 0.1 ${kgs}^{-1}$ into a measuring bowl on top of some accurate scales (measuring the force converted into a mass)from a height of ...
0
votes
1answer
110 views

Questions related to resonance/standing-waves and sound

I understand resonance for a simple harmonic oscillator but not for more complex systems like standing waves. How can I be in resonance with the normal mode in an organ pipe? I understand that the ...
0
votes
1answer
30 views

A block is rotated with $ω=a\cdot t$ [closed]

A block of mass $m$ lies on a table. The coefficient of friction between the table and the mass is $μ$. The table is rotated around where the following relation holds: $$ω=a\cdot t$$ (where t is ...
1
vote
1answer
58 views

Is velocity responsible for motion or motion responsible for velocity? [closed]

It really seems to be rather awkward to ask a question like this, but after recent studies of philosophical treatment of instantaneous rates by Zeno & his disciples, I decided to post this ...
2
votes
5answers
305 views

Is this expression for the kinetic energy of a spinning disk revolving about a second axis correct?

My question is motivated from a question from another user. You can see the configuration of the rotating system here: One disk/ring in double rotation and sum of energy. I am not interested in all ...
4
votes
5answers
567 views

Normal reaction - force without acceleration

When a body lies on the surface of the Earth it is under the influence of gravity. The force on the body due to gravity causes it to exert a force on the ground and the normal reaction acts in the ...
0
votes
2answers
548 views

Different directions of frictional force when objects are rolling

My textbook has two instances of rolling bodies (smooth rolling). In the first, the body is rolling on the horizontal floor with some acceleration of its centre of mass. In this case, the book says ...
2
votes
1answer
69 views

Fluid Dynamics Tsunami

I have been given a energy head (pressure) in meters for a given tsunami on land. My question is if the tsunami hits a wall 1 meter by 1 meter, is it possible to calculate the height it will reach. ...
2
votes
4answers
692 views

Why can't impulse be instantaneous?

We know from 2nd law of motion that $$\vec{F} = \frac{d\vec{p}}{dt}.$$ Now, a rate of change can be instantaneous. So, rate of change of momentum is instantaneous. But I doubt how can there be ...
0
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3answers
89 views

How much does the Earth's population affect the force of gravity? [duplicate]

If everyone on earth except one person were to gather up in one location, say the North Pole, and jump at the exact same time and stay airborne for about 1.5 sec. And that one person who did not jump ...
0
votes
1answer
38 views

The period of a mass-spring system including a pulley [closed]

A spring with spring constant $k$ is attached to a mass $m$ as illustrated in the following four set ups: Calculate the period of the motion for each of them. In cases (1) and (2) the period ...
1
vote
1answer
516 views

1D Kinematics - Relative Motion involving non-inertial frames of reference

I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
0
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3answers
88 views

Calculate average speed of projectile with air resistance

There's a project that I'm working on that been bugging me for awhile. The project involves this senario: A projectile is released at 1000 feet per second and moves in a straight line infinitely ...
13
votes
8answers
4k views

What is a rocket engine thrusting against in space?

I know Newton's third law of motion might be the answer for this but still I am wondering how the rockets could thrust in the empty space and move in the opposite direction. I guess an astronaut ...
1
vote
3answers
258 views

Confused about Newton's 3rd law

I am confused about Newton's 3rd Law. If a person jumps off the ground a force is applied both to the person and to the ground. However, as $F=ma$ acceleration experienced by the Earth is much less ...
3
votes
1answer
3k views

How to understand the work-energy theorem?

How to understand the work-energy theorem? I took a short lecture on physics for engineering last week. The lecturer emphasized that the work done on an object will cause the kinetic energy change as ...
0
votes
6answers
400 views

Why is kinetic energy stored as potential energy in a body during its motion against gravity?

Everyone knows kinetic energy is converted to potential energy in the body when it moves up against the earth's opposing gravitational force. But I am facing some problem with this. What I learnt ...
1
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2answers
54 views

What are the conditions for a complete circular motions?

Im a high school student and last week I learnt about vertical circular motion was thinking about this today, that what conditions are to be met in order to complete circular motion. First I thought ...
1
vote
0answers
26 views

hydrodynamic entrance length [developing flow]. Non-native speaker needs some help [closed]

I am currently writing my thesis in English as an non-native speaker. From time to time, I struggle quite a bit with the correct expression of the sentences. Could you have a look on the highlighted ...
3
votes
2answers
64 views

Kepler's First Law of Planetary Motion: Whats at the other focus? [duplicate]

Kepler's first law states that the orbit of every planet is an ellipse with the Sun at one of the two foci. Is there anything significant about the location, or any unusual properties about the other ...
0
votes
2answers
51 views

Power and velocity?

If $P=Fv$, power is constant and the power is the rate of change of kinetic energy, i.e. $P = d(mv^2/2)/dt$, what must $v(t)$ be to satisfy this equation?
6
votes
1answer
120 views

Will a rocket produce more thrust if fired in air, rather than vacuum?

I've been in an argument with a friend. He claims that when a rocket engine is fired in air, it get significantly more thrust due to the rocket pushing gas into the atmosphere, and the atmosphere ...
13
votes
8answers
3k views

Does leaning (banking) help cause turning on a bicycle?

I think it's clear enough that if you turn your bicycle's steering wheel left, while moving, and you don't lean left, the bike will fall over (to the right) as you turn. I figure this is because the ...
1
vote
1answer
51 views

How to find an effective spring constant of a quadratic potential

If a potential energy is given like $U(r)=A^3/r^2+2B^3r$, how do I find the effective spring constant using Taylor Expansion? I compared spring constant $k$ to be equal to second derivative of ...
0
votes
4answers
188 views

Two tensions in massless string

There should only be one tension in a massless string. But imagine this situation. Let a massless rope hang from a ceiling and two monkeys of different weights are holding on to the rope at two ...
5
votes
0answers
44 views

Where do Newton's laws come from? [duplicate]

I have studied physics for about three years at university but after these years I still don't know how Newton derived his laws. I know that he tried to find the best model to describe the motions ...
7
votes
2answers
429 views

What in Newton's three laws of motion is original and not a paraphrasing of his predecessors?

The three laws are: First law: The velocity of a body remains constant unless the body is acted upon by an external force. Second law: The acceleration a of a body is parallel[disambiguation needed ...
0
votes
0answers
22 views

In the formula for the change of frame of reference, which term(s) is/are the centrifugal/centripetal acceleration?

This is the formula for the change of frame of reference for the acceleration: I have a book where it is written that: The first term is the absolute acceleration. The second term is the relative ...
0
votes
1answer
45 views

Friction because of Earth's rotation

Is there some force of friction that acts on bodies due to rotation of Earth. We all know earth is an non inertial frame. If there is some frictional force is there some way to prove it. What i mean ...
1
vote
1answer
171 views

Tangential and radial acceleration in projectile motion

I'm currently learing kinematics, specifically projectile motion and as an example in my textbook is a bullet fired at some angle. I understand the derivation of formulas to describe that motion and ...
7
votes
1answer
266 views

Where is the “event horizon” on a basketball hoop?

I'm watching a lot of basketball this month. A common event is the ball going part way into the hoop and then coming out again. Announcers sometimes claim that the ball was "halfway through" when it ...
3
votes
1answer
109 views

Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
1
vote
2answers
36 views

Meeting point of one falling object and a climbing one [closed]

We have this red ball, that falls free, with no inicial velocity, off of the top of a building 60 meters high. A green ball is launched vertically, upwards, with inicial velocity of 20 m/s, after 2 ...
1
vote
1answer
47 views

Indicate if objects after collision will stick

Is it possible to indicate if objects after collision will stick together knowing their properties(materials,hardness,etc)?
0
votes
1answer
47 views

Affect on Spring constant on cutting the spring into 2 unequal parts

Question : A uniform spring with a constant 120 N/m is cut into two pieces, one twice as long as the other. What are the spring constants of the two pieces? I know that when a spring is cut ...