Questions tagged [acceleration]

The rate of change of velocity of a body per unit of time.

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231
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11answers
52k views

Don't heavier objects actually fall faster because they exert their own gravity?

The common understanding is that, setting air resistance aside, all objects dropped to Earth fall at the same rate. This is often demonstrated through the thought experiment of cutting a large object ...
122
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10answers
25k views

Why do spaceships heat up when entering earth but not when exiting?

Recently I read up on spacecrafts entering earth using a heat shield. However, when exiting the Earth's atmosphere, it does not heat up, so it does not need a heat shield at that point of time yet. ...
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3answers
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In a roller coaster, does the rear car have a higher acceleration/speed?

I am wondering about this question since I asked myself: why do people feel more weightless in the rear car of a roller-coaster than in the front car? To feel the effect of weightlessness, you must ...
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4answers
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If I'm floating in space and I turn on a flashlight, will I accelerate?

Photons have no mass but they can push things, as evidenced by laser propulsion. Can photons push the source which is emitting them? If yes, will a more intense flashlight accelerate me more? Does ...
57
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7answers
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Does a charged particle accelerating in a gravitational field radiate?

A charged particle undergoing an acceleration radiates photons. Let's consider a charge in a freely falling frame of reference. In such a frame, the local gravitational field is necessarily zero, ...
54
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4answers
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How and why do accelerating charges radiate electromagnetic radiation?

Let's consider it case by case: Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property. Case 2: Charged particle started moving (it's accelerating)....
53
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10answers
34k views

Why does a free-falling body experience no force despite accelerating?

Note: For the purposes of my question, when I refer to free fall assume it takes place in a vacuum. From my (admittedly weak) understanding of the equivalence principle, falling in a gravitational ...
49
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14answers
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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 ...
49
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6answers
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Does a constantly accelerating charged particle emit EM radiation or not?

The Abraham-Lorentz force gives the recoil force, $\mathbf{F_{rad}}$, back on a charged particle $q$ when it emits electromagnetic radiation. It is given by: $$\mathbf{F_{rad}} = \frac{q^2}{6\pi \...
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11answers
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Why can electric cars recoup energy from braking, but a spaceship cannot?

It is said that in a spaceship, you need to spend as much energy to brake as you spent for accelerating. An electric car, however, charges its batteries while braking, thus it actually recovers energy ...
42
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3answers
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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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5answers
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Why do heavier objects fall faster in air?

We all know that in an idealised world all objects accelerate at the same rate when dropped regardless of their mass. We also know that in reality (or more accurately, in air) a lead feather falls ...
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5answers
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Slinky base does not immediately fall due to gravity

Why does the base of this slinky not fall immediately to gravity? My guess is tension in the springs is a force > mass*gravity but even then it is dumbfounding.
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10answers
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Why is acceleration expressed as m/s/s?

I'm a philosophy student (I, regrettably, don't know calculus or much physics). Last year I spent some time learning how work, power, speed, velocity, energy, force, and acceleration relate. But I was ...
26
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4answers
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What would put a harddisk drive (HDD) under 350G's of force?

I always see the label and it says 350G's withstandable. What would put this over 350G's? Is it even possible to hit 350Gs of force to a hard drive?
24
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4answers
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Is there a maximum possible acceleration?

I'm thinking equivalence principle, possibilities of unbounded space-time curvature, quantum gravity.
23
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3answers
1k views

How is the energy loss by an accelerating charge expressed in the equations of motion?

I understand how, and why, an accelerating charge emits radiation, and loses energy in the process, as well as the Larmor formula for the power, and its derivation. However, in classical mechanics, ...
22
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8answers
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Mass and Newton's Second Law

While trying to understand the second law of Newton from "An Introduction to Mechanics" by Kleppner and Kolenkow, I came across the following lines that I don't understand: "It is natural to ...
21
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6answers
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Can an object *immediately* start moving at a high velocity?

What I mean is, suppose a ball is fired from a cannon. Suppose the ball is moving at 100 m/s in the first second. Would the ball have started from 1m/s to 2m/s and gradually arrived at 100m/s? And is ...
20
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7answers
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Why doesn't the Earth accelerate towards us?

According to Newton's third law of motion that states that every action has an equal and opposite reaction. So, if the Earth exerts a gravitational pull on us (people) then even we should exert a ...
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8answers
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Would it help if you jump inside a free falling elevator?

Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?
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1answer
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What came first, Rice Crispy or “Snap,” “Crackle,” and “Pop”? [closed]

The fourth, fifth, and sixth derivatives of position are called "Snap" "Crackle" and "Pop". What came first, the rice crispy characters, or the physics units?
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3answers
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Do accelerated charges radiate or not? [duplicate]

This questions has been asked all over the net (here included) but I can't find a satisfactory answer or discussion. Some say it does not radiate if the acceleration is caused by a uniform gravity ...
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7answers
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Is there a limit to acceleration? [duplicate]

As we all know the speed of light is the limit at which energy/matter can travel through our universe. My question being: is there a similar limit for acceleration? Is there a limit to how quickly ...
18
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9answers
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The instant an accelerating object has zero speed, is it speeding up, slowing down, or neither?

This problem is from Khan Academy. Specifically for the blue point circled in red, the answer is that at this blue point, the object is neither speeding up nor slowing down. When I think about the ...
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5answers
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What happens when the drag force exceeds the weight of an object falling into earth?

Let's say a meteor is coming towards earth. It's not accelerating, but it does have an initial velocity. This meteor is shaped so it has an insane amount of drag, enough to even exceed its weight (not ...
17
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6answers
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Why do two bodies of different masses fall at the same rate (in the absence of air resistance)?

I'm far from being a physics expert and figured this would be a good place to ask a beginner question that has been confusing me for some time. According to Galileo, two bodies of different masses, ...
17
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6answers
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Zero velocity, zero acceleration?

In one dimension, the acceleration of a particle can be written as: $$a = \frac{dv}{dt} = \frac{dv}{dx} \frac{dx}{dt} = v \frac{dv}{dx}$$ Does this equation imply that if: $$v = 0$$ Then, $$\...
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4answers
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Acceleration in special relativity

I am currently studying the motion of relativistic charged particles in electromagnetic fields. More exactly, we first derived the equation of motion in the 4-vector formalism. I was a bit confused ...
17
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6answers
646 views

Can you jump higher if you run? If so, why? (High jumping)

I have often wondered why high jumpers can jump higher if you run. The way I see it is that you only build up horizontal speed, and since you're running on a plane, I cannot see how this speed can be ...
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7answers
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Why doesn't the Earth's acceleration towards the Moon accumulate to create noticeable motion of the earth, towards the moon

I get that Earth's mass is very large, so its acceleration is very tiny. But wouldn't the acceleration accumulate over a period of time and become noticeable?
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9answers
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How can there be weight without movement? [duplicate]

Weight is a force. Force is mass × acceleration. When I'm standing motionless on the scale, how do I have a weight greater than $0~\mathrm{N}$ when my mass is $90~\mathrm{kg}$ and my acceleration is ...
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3answers
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How does anything move? [duplicate]

So in order for two things $A$ and $B$ to move apart, for example, relative to each other, $B$ can be set into motion away from $A$. This means that we have to increase $B$'s velocity and therefore ...
16
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5answers
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How to get distance when acceleration is not constant?

I have a background in calculus but don't really know anything about physics. Forgive me if this is a really basic question. The equation for distance of an accelerating object with constant ...
16
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2answers
8k views

Relativistic centripetal force

The thought randomly occurred to me that a circular particle accelerator would have to exert a lot of force in order to maintain the curvature of the trajectory. Many accelerators move particles at ...
15
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5answers
24k views

How fast would someone have to run to travel vertically up a wall?

I am currently doing a physics project on the effects of so-called 'super-speed'. I was wondering how fast you would have to run to vertically travel up a wall? That is, to negate the force of gravity....
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2answers
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Why do accelerating bodies have an event horizon?

I read in a book named "Three Roads to Quantum Gravity" written by Lee Smolin that any accelerating body always have some hidden region of space-time from which light is never able to catch up with ...
15
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4answers
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Does velocity or acceleration cause time dilation?

What causes time dilation? Acceleration or velocity? I've seen multiple comments on this forum that assert velocity is the cause, but that doesn't seem right to me. You can't have velocity without ...
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5answers
6k views

How to brake 'beautifully'?

Sometimes when I'm driving my car, I play a "game" against myself in which I try to minimize the deceleration felt by passengers (including myself) while still braking in a reasonable short space. I ...
14
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3answers
3k views

Why doesn't gravity speed up light?

We know that gravity speeds up a body; for instance, a meteor which enters the earth gets constantly accelerated up by earth's gravity. And from relativity we know that light bends near a massive body,...
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5answers
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How do I calculate the distance a ship will take to stop?

I am a River Pilot and drive ships for a living. These ships are very large and range up to 160,000 Metric Tons. I am trying to figure out how to calculate the distance to stopping. I have a basic ...
14
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2answers
353 views

Can the question of a gravitationally accelerated charge radiation be tested experimentally?

I know that the question of radiation from a gravitationally accelerated charge has been discussed extensively at Does a charged particle accelerating in a gravitational field radiate?. Yet the ...
13
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5answers
2k views

What is the best path for a given initial and final state?

I am trying to calculate an efficient acceleration curve given starting and final positions and velocities. I'm assuming no friction, and that the acceleration can be applied in any direction at any ...
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5answers
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What force causes the ball to move up?

Let's consider this super-simple example. The ball (mass $m$) is moving from position 1 to position 2 at constant horizontal velocity $v$ until the ball reaches the red arrow (in position 1, it has ...
13
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5answers
757 views

Why $(apparently)$ is the rotation of Earth not congruent/similar to Uniform Circular Motion? [duplicate]

Okay, so this may seem a very "simple" question. I quote few lines from one website: "We can’t feel Earth’s rotation or spin because we’re all moving with it, at the same constant speed." "...
13
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4answers
281 views

Problems in the relation $a=v\frac{\mathrm{d}v}{\mathrm{d}x}$

We all know $a = \frac{\mathrm{d}v}{\mathrm{d}t}$. A little application of the chain rule leads to the relation $$a=v\frac{\mathrm{d}v}{\mathrm{d}x}$$ But the above equation shows that $a=0$ whenever $...
13
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4answers
668 views

Is there an easy way to show that $x^2-t^2=1/g^2$ for a (relativistic) body undergoing acceleration g?

A professor asked me about the (c=1) equation: $$x^2 - t^2 = 1/g^2$$ which I used in a paper. Or with $c$: $$x^2 - (ct)^2 = c^4/g^2.$$ I told him that it was the exact equation of motion for a ...
13
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4answers
1k views

Which clock is the fastest inside an accelerating body?

The picture shows an accelerating spaceship with two clocks inside it. It is so far away from all other bodys that gravity is of no importance. Will the bottommost clock be slower than the topmost ...
13
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3answers
927 views

Is acceleration an average?

Background I'm new to physics and math. I stopped studying both of them in high-school, and I wish I hadn't. I'm pursuing study in both topics for personal interest. Today, I'm learning about ...
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9answers
3k views

How do we know that $F = ma$, not $F = k \cdot ma$

It seems intuitive that $a\; \propto \frac{F}{m}$, as the greater the force that is applied on an object, the greater its acceleration will be. Inversely, the greater the mass of the object, the ...