# What is Accelleration: Definition and 21 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,

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. V

### Calulate the distance of objects in Earth's orbit

Homework Statement I am working on a report dealing with the velocity and acceleration of objects in Earth's surface based on distance from the Earth and thus far I have used the orbital speed equation and the acceleration equation. To get dive deeper into the math I would like to attempt to...
2. ### Acellerating car vs constant speed car

Hi, I've been dsicussing this with som friends, and would be thankful if someone took the time to explain it to me :) The scenario: Car A travels at constant velocity (80km/h) along the road and hits a brick wall. Car B acellerates upward towards 100km/h, and at excactly the moment it passes...
3. ### Accelleration of a static body in wind

Homework Statement I drop a 50mm sq concrete cube fom a notional tower into a steady horizontal wind stream of 10m/sec. Homework Equations How long before the cube reaches the wind spead What is the accelleration How far will the cube have traveled down range The Attempt at a Solution
4. ### Determining Direction of Acceleration in Pulley Problems

Homework Statement In pulley problems, how do you determine the direction of accelleration? My teacher said that acceleration is in the direction of the heavier mass or the steeper incline. Is this true? What if you had two objects of equal mass and only one was on an incline? Homework...
5. ### Predicting Peak Displacement in Imbalanced Rotating Drum

If I am attempting to prevent a suspended motor-rotating imbalanced drum of high mass from colliding with its enclosure, how can I attempt to predict the maximum displacement from a balanced center of rotation if I have only a single sensor that can accurately measure(1000 samples/sec)...
6. ### Plotting a graph of accelleration agains displacement (x)

Plotting a graph of acceleration agains displacement (x) A mass of 0.3kg suspended from a spring of stiffness 200Nm-1. If the mass is displaced by 10mm from its equilibrium position and released calculate: A) frequency of vibration B) max velocity C) max acceleration D) mass...
7. ### Solving for Accelleration with only Coeffifcient of Friction, and mass

Homework Statement The coefficient of kinetic friction between rubber tires and wet pavement is 0.50. The brakes are applied to a 750kg car traveling 30.0 m/s and the car skids to a stop. What would be the magnitude and direction of the acceleration on the car? u = 0.50 m = 750kg V(i) =...
8. ### Non constant accelleration equation(s)

Hey guys, it's been awhile since I've been in the class room and I'm a bit fuzzy on non-constant acceleration problems. This actually started with a something of an amorous note sent to a lady friend, with the general idea that there is always a (small) gravitational force experienced between...
9. ### Vectors - Displacement to Accelleration

Homework Statement An object moves with its position obeying x=5t^2-6t^2 and y=3t^-1+4t^4. What is the magnitude of its acceleration at t=1s; a)57 m/s^2 b)34 m/s^2 c)26 m/s^2 d)44 m/s^2 e)0 m/s^2Homework Equations x=5t^3-6t^2 y=3t^-1+4t^4 The Attempt at a Solution Second derivative of the...
10. ### Expansion speed and accelleration question

Expansion "speed" and accelleration question I was reading about how the OU was once the size of a grapefruit, which prompted me to think about expansion acceleration. At the time that the OU was the size of a grapefruit, the universe had to be expanding faster than light, otherwise the OU...
11. ### Pulley connects 2 masses, problem with inertia to accelleration calculation

Homework Statement Given is the setup in the attachment, I think the values speak for itself. Additionally, there is a friction coefficient of 0.36 that works in on the 2 blocks. So in short: 2 masses (1 one a slope), connected through a pulley, that does have friction and to complete...
12. ### Centripetal Accelleration (Rotating object on a string)

I'm having trouble solving the following problem: An 80cm string with a mass attached to the end is rotated at a rate of one revolution per second. Assuming the force of gravity is 9.8 m/s^2, what is the angle made with the vertical by the string? [My words, but these were all the variables...
13. ### Maximum Accelleration Up Hill?

Homework Statement cross-country skier is going up a slope at angle 5º to the horizontal. She is skating so only her skis provide the propulsion (i.e. she does not push with her ski poles). The static and kinetic friction coefficients for this situation are μs = 0.12, μk = 0.07 respectively...
14. ### Equilibrium: Pendulum from a ceiling to determine accelleration.

Homework Statement As an airplane accelerates along a horizontal runway, a pendulum hanging from its ceiling is displaced 12 degrees from the vertical. Calculate the acceleration of the plane. The Attempt at a Solution After drawing my diagram, i see that there is a cord supporting the...
15. ### Net acceleration = gsin(theta) = 9.8sin10 = 0.98m/s/s

Homework Statement I am having some trouble finding out exactly how I could find net acceleration. I know how to use it for finding force of drag, and other formulas, but for a project I need to actually find the net acceleration of me throwing a baseball. This is a sample problem, that I...
16. ### Accelleration and dispacement of planes and babiess

one type of aeroplane has a maximum acceleration on the ground of 3.5ms-2 a)for how many seconds must it accellerare along a runway in order to reach its take-off speed of 115ms-1? b) what is the minimum length of runway needed for it to reach this length? ummm, not entirely sure av...
17. ### Can Photons Have Acceleration? The Uncertainty Principle and the Speed of Light

Well, there has been another thread about the accelleration of photon, but it is when the photon move from one medium to another. Now i just imagine when i start to turn the light bulb on, the light also starts to propagate at c. So should photons have a certain accelleration value consequently?
18. ### AZING!Acceleration Through a Curve: How to Calculate and Understand It

If a car gradually changes a direction of 90 degrees at constant speed of 200 m/s over a time period of 20 seconds, then what is the accelleration? I don't know if the way I worked it was correct. I think the only assumption is that the acceleration is constant...
19. ### Calculating the gravitational accelleration on the surface of a planet

Why doesn't this force give the gravitational acceleration on the surface of the earth? a = G \cdot \frac{m}{r^2} I would think that it could be derived from the law of universal gravitation: F = G \cdot \frac{m_1 \cdot m_2}{r^2} Since F = m_2 a
20. ### Help needed with accelleration problem

help needed with accelleration problem...urgent! I am having trouble wiht one of the questions on my first physics HW asignment. I've tried solving it different ways but can't seem to get the correct answer. the question reads: An engineer in a locomotive sees a car stuck on the track at a...
21. ### Calculating weight & accelleration due to gravity on other planets Help please

Alright, well this problem was too hard to explain, so I just decided to scan it ;). Here's the problem: http://img108.exs.cx/img108/5815/approb.gif I'm pretty sure I'll be able to figure out everything else once I get part (a). But I don't know where to start with this. Thanks.