# Questions tagged [newtonian-mechanics]

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 concepts, use [classical-mechanics]. For Newton’s description of gravity, use [newtonian-gravity].

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### What does the Moon's orbit around the Sun look like?

I'm curious as to what the Moon's orbit around the Sun looks like. If there's an answer, what's the intuition for it? Here are some things I'm assuming when trying to tackle this question: The Moon's ...
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### Why is torque not measured in Joules?

Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$. This means the units of torque are Newton meters. Work & Energy are also measured in Newton ...
8k views

### Principle of physics used in the lift of skateboard

What is the principle of physics used in this popular stunt? Initially, I thought aerodynamics due to an increase in the angle of attack, but its magnitude is not sufficient to balance the whole body ...
38k views

### Proof that the Earth rotates?

What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis? By basic physics I mean the physics that the early physicists must've used to ...
7k views

### What allows a pull-back toy car to drive further than it was pushed?

Imagine you have a pull back toy car. Its back part is on $x_0$. You push it down and move it in the back direction to the point $y$ (not marked): Then you leave the car to move away: Then you mark ...
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### Why does the speed of a ping pong ball increase when the space in which it can bounce decreases?

I was playing table tennis the other day when I my ball fell off the table. I placed my paddle above it in order to slow it down, and then I brought the paddle to the ground so that the ball would ...
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### Freefall into snow

In the movie Frozen, the following dialogue takes place: Anna: "It's a hundred-foot drop." Kristoff: "It's two hundred." Anna: "Okay, what if we fall?" Kristoff: "...
22k views

### Why doesn't a braking car move backwards?

The net force on an object is equal to the mass times the acceleration, $F = ma$ When I brake on a (moving) car, the net force is negative, therefore causing the resulting acceleration to also be ...
20k views

### How do bicycle spokes work?

As you know, it is quite obvious that bicycle spokes attach the hub in the center to the rim. What else do they do? If you compare the wheels today with the ones from ancient times, there are more ...
6k views

### Why do rocket engines have a throat?

Diagrams of rocket engines like this one, (source) always seem to show a combustion chamber with a throat, followed by a nozzle. Why is there a throat? Wouldn't the thrust be the same if the whole ...
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### Why don't all objects bounce like rubber balls?

Some things don't bounce like rubber balls do. For example, books don't bounce much when dropped. Why is it that some things bounce while others don't?
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### Is there an underlying physical reason why the Coriolis force is similar to the magnetic component of the Lorentz force?

I couldn't help but notice that the expression for the magnetic component of the Lorentz force, $$\mathbf F = q\,\mathbf v \times \mathbf B\,,$$ is very similar in its mathematical form to the ...
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### How does tilting a bike make it turn sharper?

Note that my question is not why do you tilt your bike when on a curve. It's about the reduction in turning radius when one tilts the bike inwards. Short to-the-point answers are welcome.
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### Is it really better for the environment if I take the stairs as opposed to a lift? [closed]

This question is inspired by a sign I saw at a lift, which said something like: Going up 1 floor or down 2 floors? Take the stairs, it's better for your health and for the environment. There's no ...
24k views

### Why is bench pressing your bodyweight harder than doing a pushup?

Why does bench pressing your own bodyweight feel so much harder than doing a push-up? I have my own theories about the weight being distributed over multiple points (like in a push-up) but would ...
19k views

### If Newton's third law is true, why can we sink in sand? [duplicate]

Newton's third law of motion states that every action has an equal and opposite reaction. That is the reason we do not sink into the earth, because when our weight exerts a force on the earth it also ...
8k views

### Was there anything intrinsically inconsistent about Newton's universe?

I am not a physicist - just a curious person. We know from observation that Newton's formulation of physics is incomplete. We could suppose that, on a planet of perpetual fog, no-one would have ...
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### What is behind the definitions of work and energy?

I am aware that there appear to be many similar questions on this site, but that is just because of the misleading title. I could not think of a better title that illustrates how different is this ...
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### Do identical starting conditions always lead to identical outcomes?

My friend and I are discussing whether or not physical phenomena are deterministic. Let's say, for example, that we have a 3-dimensional box with balls inside of it upon which no gravitational forces ...
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### Does centrifugal force stiffen a rotating blade?

I'm a helicopter pilot with limited physics knowledge (units in BSc and HNCs). I have recently challenged an assertion that rotating blades are stiffened by centrifugal force. In My mind, stiffness ...
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### Why does this object periodically turn itself?

See below gif image taken from here. Or see this Youtube video about 30 sec in. Is this a real effect? Why does it seem to turn periodically? Can it be explained by classical mechanics alone? Is ...
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### For collision, physical contact is not a necessary condition. Why?

In my textbook, it is written that "For collision, physical contact is not a necessary condition". How can collision occur without physical contact? If there is no physical contact, then there ...
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### How does 'Tear Here' work?

How does 'Tear Here to Open' work? Why is it easier to tear there as opposed to anywhere else? What is its physics?
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### Pouring water in an aircraft while upside down?

What is the physics behind the following photo? Someone had told me that this is because the aircraft might be moving towards a lower altitude, but I am still not sure.
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### If I drop a ball in an accelerating rocket, will it bounce? If so, how?

Einstein's equivalence principle says that you cannot distinguish between an accelerating frame or a gravitational field. However, in an gravitational field, if I drop a tennis ball, it will bounce, ...
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### Why does one experience a short pull in the wrong direction when a vehicle stops?

When you're in a train and it slows down, you experience the push forward from the deceleration which is no surprise since the force one experiences results from good old $F=m a$. However, the moment ...
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### Newton's 3rd law… hitting drywall (which I break) vs hitting a brick (which breaks me)?

According to the Third Newton's law of motion: For every action there is an equal and opposite reaction. So, I understand that if I hit a brick wall with $50\, \mathrm{lbs}$ of force, the brick ...
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### If the gravitational force were inversely proportional to distance (rather than distance squared), will celestial bodies fall into each other?

If gravity was inversely proportional to distance, will the dynamics of celestial bodies be much different from our world? Will celestial bodies fall into each other?
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### If the ground's normal force cancels gravity, how does a person keep rotating with the Earth?

When I am on earth, the weight of my body is countered by the reaction of the ground. So, there is no net force acting on me. But I am spinning with earth. But if there is no centripetal force then ...
16k views

### Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table

I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. ...
9k views

### What will happen to a ball kept on a frictionless inclined plane?

I was wondering about this question since I learned about rolling motion in the chapter on rotational mechanics. I was unable to come to a solid conclusion due to the reasons mentioned below. The ...
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### Intuition as to why the orientation (of a 3D object) is not a conserved quantity?

Say you start off floating in space, in a fixed position and orientation, with zero linear and angular velocity, with no external forces. So you are a closed mechanical system. By twisting your body ...
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### When you hit a baseball, does the ball ever travel faster than the bat?

It seems impossible, yet I'm thinking that maybe because the ball compresses against the bat a bit it acts a little like a spring, and DOES travel faster than the bat? EDIT: This is just a ...
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### How does rotational “artificial gravity” differ from normal gravity?

I am not a physicist, just a curious mind. I was reading a novel by Iain Banks where it was mentioned, that shifting from artificial rotational "gravity" (in space, on a rotating space craft) to real ...
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### Why do we need to know the shape of the slide to find the time to slide down it?

In my physics book after this solved example: A child of mass $m$ is initially at rest on top of a water slide at height h = 8.5m above the bottom of the slide. Assuming that the slide is ...
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### Why does my ID card oscillate sideways when walking?

When I was going to my school with my ID card hanging around my neck, it started doing oscillations like a pendulum. I was moving forward and it was oscillating left to right and right to left. What ...
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### Supergun Launching of Satellites

I should say first that I don't believe this is a feasible launch method, otherwise NASA and other space agencies would be using it by now. It's based on this BBC news story Saddam Hussein's Supergun ...
10k views

### Does artificial gravity based on centrifugal force stop working if you jump off the ground?

In an answer to another question of mine, concerning gravity, there was a link to a video about the creation of artificial gravity, based on rotation. The question I have might be silly (or with an ...
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### 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 (so ...
8k views

### How can the Earth keep spinning with a liquid core?

In regards to the 'conservation of angular momentum' being the explanation of why celestial objects spin... If you fill a ball or any other container with a liquid and try to spin it, you will not ...
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### “Falling upward” - how far you have to be from Earth to start falling to the Moon?

Talking about gravity with my 9 y/o she asked when do we start "falling upward" to the Moon. What is the distance at which the Moon's gravitational attraction is higher than that of the Earth and thus ...
6k views

### Why does ponytail-style hair oscillate horizontally, but not vertically when jogging?

Many people with long hair tie their hair to ponytail-style: Closely observing the movement of their hair when they are running, I have noticed that the ponytail oscillates only horizontally, that is,...
70k views

### Could someone jump from the international space station and live?

Felix Baumgartner just completed his breathtaking free-fall skydiving jump from $120,000\,\text{feet} = 39\,\text{km}$ above the Earth, breaking the speed of sound during the process. I was wondering ...
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### Norton's dome and its equation

Norton's dome is the curve $$h(r) = -\frac{2}{3g} r ^{3/2}.$$ Where $h$ is the height and $r$ is radial arc distance along the dome. The top of the dome is at $h = 0$. Via Norton's web. If we put a ...
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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 ...
11k views

### Where does the extra force generated by a lever come from?

Given an object being pulled down to earth by a force of 1000 lb: If a machine were to lift it off the ground for me, and I grabbed on to the rope before it was released, there is no way in the world ...
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### Dynamics of a rotating coin

Sometimes when I'm bored in a waiting area, I would take a coin out of my pocket and spin it on a table. I never really tried to figure out what was going on. But, recently I wondered about two things:...
12k views

### 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?