Give Two Examples of Negative Acceleration

Negative Acceleration Definition

Negative acceleration, otherwise known as deceleration, is the phenomenon of an object's velocity decreasing over time at a steady rate. In simple terms, deceleration is defined as the opposite of acceleration.

Overview of Negative Acceleration

Deceleration also is known as negative acceleration. It is defined as the rate with which a moving object slows down. Deceleration can be obtained by taking the difference in initial velocity and the final velocity of an object. The result will be included with a negative sign as the velocity is decreasing. The acceleration formula can be used to calculate the negative acceleration, but the result should have a negative sign.

For a given initial velocity, final velocity and time, the deceleration is,

${\rm{Deceleration}} = \frac{{{\rm{Final\ velocity}} - {\rm{Initial\ velocity}}}}{{{\rm{Time}}}}$
$$
$a_d = \frac{{{v_f} - {v_i}}}{t}$

Where, $a_d$ is the deceleration, $v_f$ is the final velocity, $v_i$ is the initial velocity, and t is the time.

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What you'll learn:

• Negative Acceleration Definition
• Overview of Negative Acceleration
• The Concept of Deceleration
• Deceleration as a Vector
• Examples of Deceleration

The Concept of Deceleration

While travelling in a vehicle, if a forward motion is felt relative to the motion of the vehicle, that means the body is decelerating. Deceleration is a special case of acceleration in which the rate of change of velocity keeps on reducing.

Acceleration is a vector quantity that means the acceleration has a magnitude as well as  direction. For one-dimensional motion, the direction of the body is indicated by two signs, positive and negative. Simply, if the acceleration has a negative sign then the object has negative acceleration or is decelerating. Negative acceleration is calculated by dividing the final velocity minus the initial velocity by the amount of time taken by the body to reduce the velocity. If the velocity is in the positive direction, negative acceleration indicates that the object is slowing down. However, if the velocity is in the negative direction, then negative acceleration indicates that the object is speeding up. Negative acceleration is also referred to as acceleration in a negative direction.

Deceleration as a Vector

As acceleration is a vector quantity, the direction of the acceleration is the same as the change in velocity. Since velocity is also a vector, the magnitude or the direction of the velocity can be changed, meaning acceleration is a change in either speed, direction or both. On the other hand, for a slow-moving object, the direction of acceleration will be opposite to its motion. This is known as deceleration, much like a train decelerates as it comes into a station.

Deceleration is always defined as the acceleration in the direction opposite to the direction of the velocity. Deceleration always results in speed reduction. Negative acceleration is said to be the acceleration in the negative direction in the selected coordinate system.

On a velocity-time graph, a line with a positive slope represents acceleration, whereas a line with a negative slope represents a negative acceleration.

Consider the velocity-time graph shown above. There we can see that the velocity of the particle increases with the passage of time from 0 to 2 seconds. Thus, we conclude that the particle has a positive acceleration and the slope of the curve is positive in this time interval. In the time interval of 2 to 3 seconds, the velocity of the particle is constant and the slope of the curve is 0. The particle has zero acceleration in this time interval. In the time interval of 3 to 5 seconds, the velocity of the particle decreases with the passage of time. The slope of the curve is negative and the acceleration is negative.

Examples of Deceleration

• The velocity of a ball decreases with time when it is thrown vertically upwards. The acceleration of the ball thrown vertically upwards is negative. So, the ball is said to have a negative acceleration or deceleration.

• When a driver presses on the brake pedal of a car, then the car becomes slower and the velocity will start to decrease. The rate of decrease in velocity of the car per unit time is negative acceleration.

• When a train reaches the station, the speed of the train reduces, i.e. the velocity of the train keeps decreasing until its velocity reaches zero. The train comes to rest.

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Give Two Examples of Negative Acceleration

Source: https://www.chegg.com/learn/physics/introduction-to-physics/negative-acceleration

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