The rate of change of velocity of a body per unit of time.
Questions tagged [acceleration]
3183 questions
275
votes
11 answers
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 in half—the halves clearly don't fall more slowly…
ErikE
- 2,996
127
votes
10 answers
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. Why is this so? I know then when entering earth,…
QuIcKmAtHs
- 3,795
- 4
- 19
- 40
112
votes
5 answers
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). We were told that it starts radiating EM…
claws
- 7,493
82
votes
7 answers
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, and the particle does not accelerate or experience…
Sergio
- 2,705
- 1
- 23
- 34
66
votes
7 answers
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:
$$\mathbf{F_{rad}} = \frac{q^2}{6\pi \epsilon_0 c^3}\mathbf{\dot{a}},$$
where…
John Eastmond
- 6,111
66
votes
10 answers
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 field is physically indistinguishable from floating…
AdamJames
- 763
62
votes
4 answers
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 the wavelength of the light matter? Is this…
Hello World
- 725
61
votes
3 answers
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 accelerate at the acceleration of the gravity…
Citizen602214085
- 647
51
votes
13 answers
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 negative. This all makes sense, but if the…
Harnoor Lal
- 647
46
votes
11 answers
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 by braking.
Both facts somehow seem intuitive to…
Jens
- 634
- 1
- 5
- 12
43
votes
5 answers
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.
Smoke Trees
- 433
- 1
- 4
- 5
42
votes
3 answers
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, but I don't think that it will in the accelerated…
user189508
41
votes
5 answers
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 much faster than a duck's feather with exactly the…
Simd
- 1,151
36
votes
7 answers
Why can’t gravitons distinguish gravity and inertial acceleration?
If gravitons mediate the gravitational force, couldn’t the detection of gravitons by an observer be used to distinguish whether they are experiencing gravitational acceleration vs. inertial acceleration, contradictory to general relativity? If this…
Jack Edwards
- 481
- 4
- 10
31
votes
3 answers
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, when we want to find the motion of a particle, the…
roymend
- 842