What is Deceleration: Definition and 227 Discussions

In mechanics, acceleration is the rate of change of the velocity of an object with respect to time.
Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by the orientation of the net force acting on that object. The magnitude of an object's acceleration, as described by Newton's Second Law, is the combined effect of two causes:

the net balance of all external forces acting onto that object — magnitude is directly proportional to this net resulting force;
that object's mass, depending on the materials out of which it is made — magnitude is inversely proportional to the object's mass.The SI unit for acceleration is metre per second squared (m⋅s−2,




{\displaystyle {\tfrac {\operatorname {m} }{\operatorname {s} ^{2}}}}
For example, when a vehicle starts from a standstill (zero velocity, in an inertial frame of reference) and travels in a straight line at increasing speeds, it is accelerating in the direction of travel. If the vehicle turns, an acceleration occurs toward the new direction and changes its motion vector. The acceleration of the vehicle in its current direction of motion is called a linear (or tangential during circular motions) acceleration, the reaction to which the passengers on board experience as a force pushing them back into their seats. When changing direction, the effecting acceleration is called radial (or orthogonal during circular motions) acceleration, the reaction to which the passengers experience as a centrifugal force. If the speed of the vehicle decreases, this is an acceleration in the opposite direction and mathematically a negative, sometimes called deceleration, and passengers experience the reaction to deceleration as an inertial force pushing them forward. Such negative accelerations are often achieved by retrorocket burning in spacecraft. Both acceleration and deceleration are treated the same, they are both changes in velocity. Each of these accelerations (tangential, radial, deceleration) is felt by passengers until their relative (differential) velocity are neutralized in reference to the vehicle.

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  1. ejacques

    Calculating Train Deceleration: Kid's Free Fall Time

    I think, since the train is decelerate the kid will fall off at free falling. the time for that is: y=0.5*9.8*t2 ⇒ t=√(2*y/g)=√(2*3/9.8)=0.8sec. Now i think i need to find what is the distance the train is doing in this time, but i can't figure this out.
  2. Tikki

    Angular deceleration of a circular saw blade

    I tried the formula I showed up there but got 0.399 instead of 7.88rad/s^2.
  3. Z

    Angular deceleration of the Earth

    365 rotations - 365 days 365 days - 31536000 s apart from that I do not know how to continue the question
  4. Z

    Angular deceleration of a washing machine spin cycle

    6.0 rev - 1 s 1 rev - 1/6 5.0 rev - (1/6) x 5 = (5/6) s = 0.833 s I do not know how to calculate the angular acceleration
  5. S

    How to determine the car's deceleration at a point along a curve?

    So I get the exercise and all and have just solved it. But .. I kind of very very intuitively determined ##\theta## to also be the angle for the circular sector. The problem here is that my geometry bag is very weak, I didn't have any geometry in HS, will fix that sooner or later but anyway...
  6. chwala

    Find the car's speed at point when deceleration is increased - Mechanics

    Wawawawawawa! This was a tough one...:biggrin: Find the question below; Find my approach below: We have the following equations; 1. ##v=30-0.5t## 2. ##v=30-1.5t## Now the car changes its acceleration at some point i.e from ##-\frac{1}{2}## ##m/s^2## to ##-\frac{3}{2}## ##m/s^2## ... I...
  7. xwalsh

    How to find deceleration up incline

    Basically the problem is giving me an initial velocity to start with it goes up the incline before it comes back down. I know how to do everything else in the problem but solve for the initial acceleration up the incline. What would I need to calculate to solve this?
  8. T

    Elastic collision: Determine the deceleration

    My approach so far is to use F = ma. The forces acting on the block in the horizonital direction are friction and the force of the spring. Choosing the direction towards the spring as the positive axis. Therefore: F = ma -Fr - kx = ma Solving for a = (-Fr - kx)/m If I plug in values I end up...
  9. Pipsqueakalchemist

    Engineering Crate lowered by two ropes and deceleration at each point of contact with rope

    For this question, I don’t understand the steps for the relative motion part. When I try it I get angular acceleration to be zero which is obviously wrong. The solution doesn’t consider the Y distance between G and A but I don’t understand why. In the relative motion equation it’s suppose to be...
  10. T

    Rotational Dynamics - Modeling brake caliper deceleration of a chassis

    I am a junior engineer tasked with modeling the dynamics of a small research UAV after landing. The UAV has 3 tires, 1 on the nose landing gear and 2 on the rear landing gear. The rear tires are equipped with disc brake calipers. My coworker has explained that the simplified model (MODEL 1...
  11. A

    How much deceleration is reasonable for a free fall impact?

    Hi, Hope this is the correct forum for this kind of question. I am doing an explicit finite elements simulation of a tank, weighs around 7.5 Kg with internal parts, falls from 1 meter. Since I never had a validation of such an experiment I am trying to understand if the numbers are right. I...
  12. L

    Train deceleration and minimum stopping distances

    So my work includes using the acceleration formula a=delta v/t (Vrtf-Vrti)/a -> (0-54)/(-0.31) -> t=174 seconds I plug in 174 seconds to find the acceleration of the left train. and got -0.22m/s^2 I then used the displacement equation x=(1/2)at^2+Vo+So coming out with Xrt=4703m and Xlt=...
  13. jamiebean

    Deceleration of rocks sliding up a hill

    i have no idea how did the answer come in conclusion...i guess that cosθ and sinθ is referring to the 2 dimensions of the acceleration ? but how? and why?
  14. M

    Finding the 'g-force' of a decelerating falling mass.

    Hey all, I need a reality check and verification on some work I have been doing. I feel as though I might be too close to the problem now and am missing something about this. It's also been a few years since I studied physics at University, so I'm a little rusty. Problem: An initially...
  15. redtree

    I What Does a Negative Value for the Deceleration Parameter Imply in Cosmology?

    I note the general Taylor series for ##a(t)## as: \begin{equation} \begin{split} a(t)&\approx a(t_0) + a'(t_0) (t-t_0) + \frac{1}{2!} a''(t_0) (t-t_0)^2 ... \end{split} \end{equation} which I rewrite as: \begin{equation} \begin{split} a(t)&\approx a(t_0)\left(1 +...
  16. M

    B Particle Deceleration in Relativistic Jets?

    I have a question about this picture: It shows matter traveling at relativistic velocities away from a black hole: "Figure 5.21: This VLA image of the radio-loud quasar 3C 175 shows the core, an apparently one-sided jet, and two radio lobes with hot spots of comparable flux densities. The jet...
  17. K

    How to find the deceleration of a mass colliding on a spring?

    Problem Statement: A known mass at a know velocity collides on a spring of known stiffness. What is the equation that governs the deceleration of the mass, so that the force on the spring could be found? Relevant Equations: 1/2 m*V^2 = 1/2*k*x^2 + 1/2*m*(Vo)^2 Kinetic energy of mass before...
  18. Memorical

    Kinematics: time for a given acceleration, deceleration and distance

    Note: Maths has always been kinda a weak point for me in school. Anyway. From hereon I'm going to talk about this in the context of a train for simplicity, even though this is actually needed for an entirely different context - but I don't think this is relevant for the problem. In terms of my...
  19. M

    Deceleration formula for movement simulation

    Hi, i have one big problem with this simple formula, i tried many ways and combinations, but nothing worked how i wanted it. Let's assume we have a distance, let's say it's 100000 units of any type, could be virtual since i am trying to program a 3d physics engine. The object pass that...
  20. Jozefina Gramatikova

    Cosmology deceleration parameter

    Homework Statement Homework Equations modified Freidmann: The Attempt at a Solution for part b) I am not sure what to do as I am not sure what they mean by and
  21. ChrisXenon

    Problems with UK A level Physics Marking Schemes

    Hi Folks, I am a private tutor and one thing I teach is A level Physics (OCR Physics A). Am I the only person who has been sometimes baffled and deeply disappointed with some of the questions/answers? Let me explain what I mean. I see questions form which it's not possible to decide what kind...
  22. J

    Minimum deceleration to prevent a collision

    Homework Statement At a given time ##t=0##, a car 1 moving with constant velocity ##v_{1}## breaks with constant deceleration ##d##. Another car 2 at a distance ##L## behind car 1 and traveling with constant acceleration ##a_{2}## and velocity ##v_{2}## at ##t=0## brakes immediately as soon as...
  23. H

    What Magnets are best to demonstrate deceleration?

    Hello I'd like to demonstrate to students how a magnet is slowed when falling through a copper pipe due to generation of magnetic force. What type of magnet should I use? ShouId it be cylindrical or flat? Which way shouId it be magnetized? I have 3/4 inch pipe. Thanks ham1
  24. HunterB

    Comparing the deceleration of a squirrel to a WW2 airmen

    Homework Statement Compare the deceleration of the squirrel to airmen. The squirrels velocity being 7.67 (m/s) ignore air resistance, stopping distance of 3.9 cm, deceleration of an airman being 486 (m/s^2), velocity being 54 (m/s) and stopping distance of 3.0 m. Homework EquationsThe Attempt...
  25. M

    How to calculate the deceleration of the object

    Hi, i am trying to understand, how to calculate the deceleration of the object? I have a small toy car in the track, after i release the car, i want to calculate the deceleration of the car, and predict how many loops, it's going to do, after measuring the timing of some revolutions. Is there...
  26. J

    Calculating Height of Thrown Object w/ Changing Deceleration g

    Good day, I have a question regarding calculating the total reached height ##H## of an object that is thrown upwards with an initial velocity ##v_i##, while taking into account the decreasing gravitational deceleration ##g## with height as well.The formula would be something like: $$v_i \cdot t...
  27. A

    Determining camshaft deceleration rate from Follower?

    I am doing this as a hobby, trying to understanding some physics calculation for camshafts and following cam s,v,a,j. All pictures in this thread are just samples that tie to nothing much, other than just images. 1. From the 1st image above, the camshaft (emulated digital signal) is...
  28. L

    What is the velocity of a decelerating boat after 4.9 seconds?

    Homework Statement A boat, moving at the velocity of 9,9m/s turns off its engine and starts decelerating at the rate of a=-kv^2. What is the velocity of the boat after 4,9 seconds if the constant k is k=5,5m Homework EquationsThe Attempt at a Solution I tried to integrate deceleration to get...
  29. M

    Finding speed when given deceleration and distance?

    Hi! I have this homework problem that has me completely stumped. Any help is greatly appreciated! In coming to a stop, a car leaves skid marks 80m long on the highway. Assuming a deceleration of 7.00m/s2, estimate the speed of the car just before braking. I just can't figure out what formula...
  30. P

    AP PHYSICS 1 Kinematics falling with deceleration

    Homework Statement Captain American bails out of an airplane and falls 50 meters without friction. When the parachute opens, he decelerate at 2.0m/s2. He reaches the ground with a speed of 3.0 meters/sec. a.) How long is captain america in the air? do= d= vo= v=3m/s t= ? a= -9.8m/s2 ?? (this...
  31. J

    What if the actual force for a Newton was different?

    ince f=ma, and we derive whatever the force it takes to accelerate a specific mass at a specific acceleration as a unit of force. I understand this ratio of actual force will always be the same in the entire universe but is there a reason why for example 1kg accelerated a 1m/s^2=1 N which is...
  32. L

    What is the deceleration rate of a fidget spinner?

    Hi All, In a fidget spinner. Disregarding what force applied and spinner decelerate (a) at a given time (t), at what distance (s) it travel before full stop?
  33. T

    What is the deceleration of a snowboarder going up a 5.0° slope?

    Homework Statement Calculate the deceleration of a snowboarder going up a 5.0° slope, assuming the coefficient of friction for waxed wood on wet snow ( = 0.1). Homework Equations F = ma W = mg Fs = (Fn) Fk = k (Fn) The Attempt at a Solution Answer key says it's 1.83 m/s2. I fiddled...
  34. H

    What is the deceleration of the ball?

    Homework Statement The question didn't fit there. *A boy drops a metal ball from rest on sand. It hits the sand bed in one second and makes an impression of maximum depth 8mm in the sand. What is the average deceleration of the ball as it hits the sand? Assume air resistance is negligible. vi=...
  35. R

    What is the initial deceleration of the impala?

    Homework Statement On a particularly hot day at the racetrack, Dale Earnhardt's famous no. 88 Chevy impala (m = 1600 kg ) speeding at 200 mph (89 m/s) blows a gasket and the engine begins to deaccelerate. The car is shifted to neutral and coasts toward the pit lane. Neglecting all sources of...
  36. R

    I What causes the deceleration of a satellite? Space dust?

    After talking to a coworker, I looked into the wikipedia article on "Gravity of Earth". I found that the Earth's gravity is not uniform, which makes sense (never thought about it). I have always wondered why satellites de-orbit over time. Someone told me that there is enough space dust to slow...
  37. Vikinglord

    I Calculate Skydiver Deceleration Force

    I'm wondering how to calculate the force exerted on a skydiver as they decelerate from their terminal velocity of approximately 120 mph to approximately 30 mph in the course of one second, as I have seen and felt while skydiving. Thank you all in advance.
  38. P

    Deceleration distance over time

    Homework Statement :[/B] A person drives a car for 20 seconds in a straight line with an initial velocity of 20m/s. During the entire course of the journey they applied breaks causing the car to decelerate at 5m/s2. How far will it be from the starting point after the given time? Homework...
  39. S

    Is Acceleration/Decceleration smooth?

    Firstly I must say if this is in a wrong sub-forum I apologise. This is my first post and I'm new to the website so please bare with me. Also I was unsure of the Prefix so I again apologise if that to, was incorrect. But my Question is that is the acceleration (or deceleration) of an object...
  40. L

    G force and rate of deceleration

    gee i am not worthy of being here with you guys but i must know is an accelerometer's negative output due to the braking of a motor vehicle directly proportional to the the rate of deceleration of the motor vehicle and can this be predicted using a derivative function? And if I were to plot the...
  41. nysnacc

    Deceleration Calculation for Drag Force with Varying Units

    Homework Statement I forgot if the deceleration is -0.003v or same here -0.003v2 Homework Equations v = u + at (first acceleration) dv/dt = a (deceleratioin) = -0.003v^2 The Attempt at a Solution From first equation, 342.2 = 0 + 30*t1 t1= 11.407s From 2nd equation, dv/v2 = -0.003...
  42. B

    Deceleration and Acceleration: Opposites or One and the Same?

    Homework Statement If you decelerate in one direction, are you accelerating in the opposite direction? Ex. You are standing in an elevator and are slowing down, going upwards- are you accelerating downwards since you're decelerating in the opposite direction, upwards? Homework Equations -...
  43. A

    Finding deceleration of a ball?

    Homework Statement How to find deceleration of a ball that is hit, given the ball: mass=0.1kg F=20N is hit by a bat for 0.01s has an acceleration of 200ms^-2 when hit by bat speed=2m per sec travels 0.01m as it is being hit by the bat Was initially at rest.Homework Equations a=(v-u)/t The...
  44. Eclair_de_XII

    How to find deceleration to stop collision with moving body?

    Homework Statement "When a high-speed passenger train traveling at 161 km/h rounds a bend, the engineer is shocked to see that a locomotive has improperly entered onto the track from a siding and is a distance D = 676 m ahead (Fig.2-29). The locomotive is moving at 29.0 km/h. The engineer of...
  45. Grace204

    Finding displacement through velocity and deceleration

    Homework Statement a car with an initial velocity of 10.0 m/s (W) decelerates at -2.00 m/s (s to the power of 2) (W) reaching a final velocity of 5.00 m/s (W). What is the displacement of the car? Homework Equations Δdisplacement = (final velocity to the power of 2 - initial velocity to the...
  46. H

    Deceleration time for studded snow tires

    I have data from road tests done in someone else's experiment that show that a car with studded snow tires will take on average 23 meters to stop from 25 mph on packed powder at 0 degrees C. From that information, can I figure out what length of time it takes for the car to stop? Can I...
  47. H

    Deceleration rate with studded snow tires

    A car going 25 mph with studded tires on packed powder stops in 20 meters. What will be the stopping distance if it is going 20 mph? We do not know the mass of the car, but perhaps it is accurate to create an acceleration constant that will apply for other speeds? a=v/t and v=d/t so therefore...
  48. electrodruid

    What factors affect car braking distance?

    I'm a game programmer trying to write code to simulate a variety of cars braking at different speeds and on surfaces with different coefficients of friction. For now, consider that I'm interested in a fairly wide range of cars (people carriers, hatchbacks, saloons, sports cars etc) but that...
  49. T

    Force provided during deceleration?

    Homework Statement A spacecraft with a mass of 9100kg (incl fuel) traveling at 8 m/s Rockets fire for 10 seconds burning 100kg of fuel slowing the spacecraft to 0.03 m/s What is the force the rockets provided during the 10 seconds? Homework Equations acceleration = ∆v/t F = m x a[/B]...