How can acceleration be negative?Acceleration is change in velocity( change in displacement over change in time)over change in time. Even if an object is slowing down, velocity is positive. So what is negative velocity?
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anonymous
ANSWERS: 10
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I always thought slowing down was negative acceleration, and that there's really no such thing as deceleration. PS: After re-reading your question a few times...velocity is not negative. If you're going 50 MPH and slow down by 10 MPH, your acceleration was -10 MPH but your velocity is 40 MPH. It's always 0 or a positive value, AFAIK.
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Acceleration is the rate at which an object's velocity changes with time. Negative accelaration indicates that an object is slowing down. The scientific definition is not the same as the common definition. http://www.google.com/search?hl=en&pwst=1&defl=en&q=define:Acceleration&sa=X&oi=glossary_definition&ct=title
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Velocity has a direction, so must be expressed in a co-ordinate system. 20mph is a speed, 20mph due north is a velocity. A velocity in the increasing direction of the co-ordinate system is a positive velocity whereas a velocity in the decreasing direction of the co-ordinate system is negative. An acceleration which makes the velocity less negative or more positive is a positive acceleration. An acceleration which makes the velocity less positive or more negative is negative.
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The CHANGE is negative since your velocity is constantly decreasing. It is because of this that the term "negative acceleration" is used. You could use "deceleration" as well. Acceleration can be negative, velocity can never be negative. It just changes its direction.
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While slowing down velocity is positive, but the rate of its change is negative. See, acceleration i.e rate of change of vel is (final velocity - initial vel)/time . final vel is smaller than initial, so acceleration will be negative. As for the negative velocity say that you are going towards south with velocity 30 m/s then your velocity towards north is -30 m/s.
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A negative acceleration means deceleration, e.g. slowing down. A negative velocity is travelling in the direction opposite to the method you have labelled positive, e.g. Imagine a graph, if you are travelling in the +x direction you have a positive velocity... -ve x is -ve velocity :)
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Here are some ways that negative acceleration makes sense. 1) Acceleration can be defined as a vector quantity and is defined as rate of change of velocity wrt time. Thus as such it would normally make no sense to have a "negative" acceleration, yet what if you accelerate at a rate a and then reverse it -a. That's negative wrt to the first acceleration (as a scalar multiplier). 2) Often the context is an acceleration in one dimension, e.g. along a straight race track, or a body falling from a height. Wrt a single coordinate, an acceleration can be negative. 3) Combining 1 and 2: an acceleration could be in the opposite direction to some other quantity: e.g. In a simple harmonic pendulum acceleration is negative wrt to the displacement. 4) The rate of change of speed is also often (confusingly) called acceleration. As a scalar, it's rate of change can be negative.
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Acceleration = dV/dt ie rate of change of velocity. Now imagine plotting a graph of velocity against time. If an object has a decreasing velocity, the graph will have a negative gradient (a "downward" slope) Since the graph is V against t, the gradient is given by dV/dt. But we have already said that the gradient is negative, hence the acceleration is negative hope this helps... :)
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There appears to be 2 explanantions of negative acceleration. 1) when the car is slowing, velocity is still positive but acceleration is negative 2) When a car is in reverse and getting faster it has a negative velocity and a negative acceleration! Motion has to be described in terms of which direction is positive and where the start point is!
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acceleration is said to be positive (+) if the velocity increases; negative(-) if the velocity decreases or zero if there is no change in velocity.In common terms, we talk a of a car accelerating if the speed increases and braking or decelerating when the speed decreases.
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