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# Acceleration

Acceleration is a measure of the rate at which the velocity of an object is changing. If you are riding in a car traveling in a straight line at a constant 50 kilometers per hour, you experience no acceleration because the car's velocity (rate of motion) is not changing. If the car begins to speed up, acceleration occurs because the car's velocity increases. If the car slows down, negative acceleration, or deceleration, occurs because the car's velocity decreases.

## Acceleration and force

Our understanding of acceleration is due to the work of two great scientists, Italian physicist Galileo Galilei (15641642) and English physicist Isaac Newton (16421727). During the late sixteenth and early seventeenth centuries, Galileo first observed the motion of objects rolling down an inclined plane. He wrote mathematical equations that showed how the velocities of these objects increased as they rolled down the planes. These equations first described the idea of accelerated motion.

Some years later, Newton explained the observations made by Galileo. He said that the velocity of an object changes only when a force acts on that object. In the case of a ball rolling down a plane, that force is the force of gravity. Newton's discovery of the relationship between force and acceleration became one of the fundamental concepts in modern physics.

## Linear acceleration

An object moving in a straight line is accelerated only if a force acts on it. For example, imagine a ball rolling across a smooth flat surface with a velocity of 5 meters per second. Then suppose someone hits the ball lightly with a bat. The additional force on the ball provided by the bat will cause the ball to move faster.

Suppose that the ball's new velocity is 10 meters per second and that it takes 2 seconds to accelerate from its original velocity (5 meters per second) to its new velocity (10 meters per second). The acceleration of the ball, then, is the change in velocity of 5 meters per second (10 meters per second minus 5 meters per second) divided by the time it takes to increase in velocity (2 seconds), or 5 meters per second divided by 2 seconds. The acceleration is 2.5 meters per second per second. The unit of measurement used for accelerationmeters per second per secondmay sound strange, but it tells by how much the velocity (meters per second) changes in each unit of time (per second).

## Circular acceleration

The acceleration of an object depends on two factors, velocity and direction. An object that moves with constant speed but that changes direction is also accelerating. A car traveling around a curve in the road is accelerating even though its speed remains constant.

## Words to Know

Acceleration: The rate at which the velocity and/or direction of an object is changing with respect to time.

Circular acceleration: Acceleration in which the direction of motion is changing.

Force: A push or pull on an object that will accelerate an object.

Gravity: The special acceleration of 9.81 meters per second per second exerted by the attraction of the mass of Earth on nearby objects.

Linear acceleration: Acceleration in which the speed of an object is changing.

Velocity: The rate at which the position of an object changes with time, including both the speed and the direction.

Another example of circular acceleration is the motion of the Moon around Earth. The Moon travels at a constant speed in its orbit. But it also falls constantly towards Earth's surface. The force of Earth's gravity acts on the Moon not to change its speed but to change the direction in which it is traveling. Again, acceleration occurs when a force acts on an object.

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## acceleration

acceleration, change in the velocity of a body with respect to time. Since velocity is a vector quantity, involving both magnitude and direction, acceleration is also a vector. In order to produce an acceleration, a force must be applied to the body. The magnitude of the force F must be directly proportional to both the mass of the body m and the desired acceleration a, according to Newton's second law of motion, F=ma. The exact nature of the acceleration produced depends on the relative directions of the original velocity and the force. A force acting in the same direction as the velocity changes only the speed of the body. An appropriate force acting always at right angles to the velocity changes the direction of the velocity but not the speed. An example of such an accelerating force is the gravitational force exerted by a planet on a satellite moving in a circular orbit. A force may also act in the opposite direction from the original velocity. In this case the speed of the body is decreased. Such an acceleration is often referred to as a deceleration. If the acceleration is constant, as for a body falling near the earth, the following formulas may be used to compute the acceleration a of a body from knowledge of the elapsed time t, the distance s through which the body moves in that time, the initial velocity vi, and the final velocity vf:

a=(vf2-vi2)/2s
a=2(s-vit)/t2
a=(vf-vi)/t

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# ACCELERATION

A hastening; a shortening of the time until some event takes place.

A person who has the right to take possession of property at some future time may have that right accelerated if the present holder loses his or her legal right to the property. If a life estate fails for any reason, the remainder is accelerated.

The principle of acceleration can be applied when it becomes clear that one party to a contract is not going to perform his or her obligations. anticipatory repudiation, or the possibility of future breach, makes it possible to

move the right to remedies back to the time of repudiation rather than to wait for the time when performance would be due and an actual breach would occur.

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## acceleration

acceleration Amount by which the velocity (speed in a particular direction) of an object increases in a certain time.

Acceleration can involve a change in speed and direction. It is measured in metres or feet per second per second (m/s2 or ft/s2). For example, if an object accelerates from 20m/s2 to 30m/s2, it has accelerated by 10m/s2. A stone dropped over a cliff accelerates from zero velocity at a rate of 9.81m (32.2ft) per second per second, this acceleration being due to the pull of Earth's gravity. The rate of acceleration can be found by applying the equation: acceleration = (change in velocity)/(time taken for change). Deceleration is a decrease in velocity. See also gravitation

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## acceleration

acceleration A form of heterochrony in which, during the course of evolution, the rate of development of an organism is speeded up and new stages are added to the end of the ancestral developmental sequence without prolonging the total development time. The morphological outcome is an example of peramorphosis, and the developmental sequence (ontogeny) conforms to the theory of recapitulation.

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## acceleration

ac·cel·er·a·tion / akˌseləˈrāshən/ • n. increase in the rate or speed of something. ∎  Physics the rate of change of velocity per unit of time. ∎  a vehicle's capacity to gain speed within a short time.

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## acceleration

acceleration Evolution that occurs by increasing the rate of ontogenetic (see ONTOGENY) development, so that further stages can be added before growth is completed. This form of heterochrony was proposed by E. H. Haeckel as one of the principal modes of evolution.

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## acceleration

acceleration Evolution that occurs by increasing the rate of ontogenetic (see ONTOGENY) development, so that further stages can be added before growth is completed. This form of heterochrony was proposed by E. H. Haeckel as one of the principal modes of evolution.

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## acceleration

acceleration Evolution that occurs by increasing the rate of ontogenetic (see ontogeny) development, so that further stages can be added before growth is completed. This form of heterochrony was proposed by E. H.Haeckel as one of the principal modes of evolution.