The rate of change of velocity of a body per unit of time.
42
votes
9answers
7k 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 ...
11
votes
4answers
376 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 ...
10
votes
7answers
2k views
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?
10
votes
4answers
967 views
Acceleration of two falling objects with identical form and air drag but different masses
I have a theoretical question that has been bugging me and my peers for weeks now - and we have yet to settle on a concrete answer.
Imagine two balloons, one is filled with air, one with concrete. ...
9
votes
1answer
596 views
How do I calculate the (apparent) gravitational pull with General Relativity?
Assume a static metric with (known) components $g_{\mu\nu}$. I'd like to know what is the gravitational pull $g$ of a test particle placed on an arbitrary point $X$.
The gravitational pull being ...
9
votes
1answer
631 views
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?
9
votes
3answers
429 views
How do we explain accelerated motion in Newtonian physics and in modern physics?
Maybe my question will seem stupid, but I am not a physicist so I have some problems understanding a classic Newtonian experiment: in the bucket experiment, why does he have to introduce the absolute ...
8
votes
3answers
363 views
Whether $m$ in $E=mc^{2}$ and $F=ma$ are both relativistic mass?
I know that $m$ in $E=mc^{2}$ is the relativistic mass, but can $m$ in $F=ma$ can also be relativistic? If the answer is yes, then can you tell me whether this equation is valid $E=\frac{F}{a}c^{2}$? ...
8
votes
4answers
311 views
Are smaller soap bubbles more accelerated by wind?
If you blow a bunch of soap bubbles outside, and a gust of wind hits them, will the bigger ones be more or less accelerated by the wind than the smaller ones?
Intuitively, and maybe from remembered ...
7
votes
4answers
2k views
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 ...
7
votes
1answer
248 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 ...
7
votes
2answers
803 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 ...
7
votes
2answers
786 views
Should acceleration be included in state vector of a Kalman filter?
I'm developing (actually adopting existing solution) a Kalman filter to model motion of a vehicle (UAV or automobile). The state vector will include position, velocity, and, possibly, acceleration.
...
6
votes
8answers
475 views
Can you completely explain acceleration to me?
I understand what acceleration is, and I know the formula, and I understand it's a vector.
I just don't understand how the equation works exactly. I'm kind of picky, I know, but bear with me.
...
6
votes
4answers
460 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 ...
6
votes
8answers
695 views
Reactionless Drives
According to the third law of motion, you van't have an mass move in a particular direction unless there is a proportional opposite mass/acceleration ratio in the opposite direction.
No-one has been ...
5
votes
4answers
458 views
Why do we weigh less when falling?
I don't want to go to science world to find out because it would be a long round-trip.
I understand that acceleration/deceleration would effect the weight and I can also imagine that someone at ...
5
votes
4answers
114 views
Integrating radial free fall in Newtonian gravity
I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving ...
5
votes
2answers
284 views
relativistic acceleration equation
A Starship is going to accelerate from 0 to some final four-velocity, but it cannot accelerate faster than $g_M$, otherwise it will crush the astronauts.
what is the appropiate equation to constraint ...
5
votes
1answer
113 views
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.
5
votes
1answer
99 views
Measuring acceleration of a bus using water between two sheets of glass
I was riding a bus one day and noticed that the double windows had some water between them. As the bus accelerated, the water collected to the sides, first forming a trapezoid and then a right ...
5
votes
2answers
123 views
In mechanics, is shock really better expressed as jerk instead of acceleration?
Some expensive electronics or mechanical devices are designed to be shock-resistant. However, the manufacturers often market the level of shock-resistance in units of g-force (I know g-force is really ...
4
votes
5answers
4k views
Distance when acceleration 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 ...
4
votes
3answers
419 views
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 ...
4
votes
3answers
759 views
Is acceleration relative?
A while back in my Dynamics & Relativity lectures my lecturer mentioned that an object need not be accelerating relative to anything - he said it makes sense for an object to just be accelerating. ...
4
votes
4answers
219 views
Gravity from a singularity as distance approaches zero
If you had a singularity (that had mass but took up no space), what would happen to the acceleration of an object as it approached this singularity? I would assume that it would be infinite, since as ...
4
votes
4answers
699 views
Is acceleration an absolute quantity?
I would like to know if acceleration is an absolute quantity, and if so why?
4
votes
1answer
81 views
How did Newton find out force has something to do with acceleration?
Its about Newton's second law of motion,
$$F=ma.$$
It says the acceleration of an object is directly proportional to the net force and is inversely proportional to the object's mass. Yes I can ...
3
votes
5answers
553 views
Confused about the role of mass
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, ...
3
votes
5answers
372 views
If a space ship accelerated constantly, would its astronauts constantly feel the forward movement?
I know that if a space ship suddenly traveled very fast, its astronauts would be fly against the back wall, potentially getting hurt. If the space ship suddenly stopped, they would also fly against ...
3
votes
2answers
601 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.
3
votes
2answers
502 views
Does a moving escalator make it easier to walk up the steps?
I was discussing with my colleagues why it feels easier to walk up an escalator when it is moving. My natural assumption was that the movement of the escalator imparts some extra acceleration on the ...
3
votes
3answers
3k views
Ion Drive Propulsion Top Speed
I would like to know if there is some formula / graph which would provide / show the efficiency of a certain type of propeller in space. Specifically, I'm interested in the acceleration attainable at ...
3
votes
2answers
66 views
Sign of acceleration
I'm developing an application using accelerometer sensor. I'm not good at physics so forgive me if the question is trivial. If I have 3 values of acceleration: $x$, $y$, $z$, I find acceleration ...
3
votes
1answer
600 views
Is acceleration due to gravity constant?
I was taught in school that acceleration due to gravity is constant. But recently, when I checked Physics textbook, I noted that
$$F = \dfrac{G \cdot m_1 \cdot m_2}{r^2} $$
So, as the body falls ...
3
votes
2answers
485 views
Classical car collision
I have a very confusing discussion with a friend of mine.
2 cars ($car_a$ and $car_b$) of the same mass $m$ are on a collision course. Both cars travel at $50_\frac{km}{h}$ towards each other.
They ...
3
votes
6answers
157 views
Is acceleration $a = s/t^2$, or $a = 2s/t^2$, or something third?
I'm having trouble understanding some of the stuff regarding movement in my introductory physics class (I never thought I'd say that...)
Acceleration is defined as $ a = \frac{s}{t^2}.$
Distance can ...
3
votes
2answers
220 views
A simple thought experiment about traversable wormholes
Let's say I have a tube, of large radius (about 5 - 7 meters in diameter), with traversable wormholes at the ends. The wormholes are arranged as such that if something falls inside one hole from ...
3
votes
1answer
164 views
What does it mean to find acceleration in terms of g?
I'm having trouble understanding what a problem I have is seeking.
To simplify the problem:
A particle reaches a speed of 1.6 m/s in a 5.0 micrometer launch. The speed is reduced to zero in 1.0 ...
3
votes
1answer
140 views
A practical deceleration question
My friend is a U.S. Army paratrooper. Today, through an unfortunate series of events, he was jerked out of a C-17 traveling at 160 knots by his reserve parachute. First-hand accounts describe it as he ...
3
votes
1answer
103 views
Why is cosmological acceleration expressed in terms of an energy density?
In the articles that I have (tried to) read, acceleration ends up being expressed as a dimensionless constant (omega-lambda) or else occasionally in terms of a "dark" energy density. Presumably one ...
3
votes
2answers
960 views
Formulas for ball rolling in a bowl?
I'm developing a program where I've a ball/sphere rolling in a bowl from the side at top, till the center at bottom, and I'm trying to get the formulas for:
The rotation angle and the position of ...
3
votes
2answers
158 views
Nonuniform acceleration due to rubber rope
What I want:
I have a rubber rope which is $5m$ in length when not stressed and is able to stretch about $100\%$ (to $10m$ long). I want to accelerate a constant mass horizontally, which has ...
2
votes
5answers
434 views
Why doesn't an electron accelerate in a circuit?
Why don't electrons accelerate when a voltage is applied between two points in in a circuit? All the textbooks I've referred conveyed the meaning that when an electron traveled from negative potential ...
2
votes
2answers
826 views
Gravitational pull vs. acceleration due to gravity
It might seem obvious but i can't imagine how is gravitational pull is different from acceleration due to gravity?
2
votes
4answers
868 views
Physics behind Wheel Slipping
Lets say that I'm in a car and I apply full acceleration suddenly. Now, the wheels would slip and hence the car doesn't displace much.
But If I start with some constant acceleration, slipping doesn't ...
2
votes
3answers
772 views
What is the velocity area method for estimating the flow of water?
Can anyone explain to me what the Velocity Area method for measuring river or water flow is?
My guess is that the product of the cross sectional area and the velocity of water flowing in a pipe is ...
2
votes
2answers
582 views
How much effect does the mass of a bicycle tire have on acceleration?
There are claims often made that, eg, "An ounce of weight at the rims is like adding 7 ounces of frame weight." This is "common knowledge", but a few of us are skeptical, and our crude attempts at ...
2
votes
3answers
2k views
Convert acceleration as a function of position to acceleration as a function of time?
Suppose I have acceleration defined as a function of position, "a(x)". How to convert it into a function of time "a(t)"? Please give an example for the case a(x)= x/s²
2
votes
2answers
145 views
Fictitious forces confusion
I have a hard time understanding the subject of fictitious forces. Let's discuss a few examples:
1) I'm sitting inside a vehicle which is accelerating in a straight line. I feel like someone is ...
