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5

the velocity occurs, the greater the acceleration is. Acceleration is defined as

the time rate of change of velocity:

change in velocity êV

Acceleration = =

time for changing to occur T

8

Since velocity is a vector quantity, acceleration is also a vector quantity.

For an object in a straight-line motion, the acceleration may be in the same

direction as the velocity or the acceleration may be in the opposite direction of

the velocity. In the first instance the acceleration causes the object to speed up

and the velocity increases. If the velocity and acceleration are in opposite

directions, then the acceleration slows down the object, which is sometimes

called a deceleration.

9

There is one very special constant acceleration associated with the

acceleration of falling objects: the acceleration of gravity at the Earth’s surface.

It is directed downward and is denoted be the letter g. Its magnitude in the SI

system is: g = 9.80 m/s

2

. The great Italian physicist Galileo Galilei (1564 –

1642) was one of the first scientists to assert that all objects fall downward with

the same acceleration. We can state Galileo’s principle as follows: if frictional

effects can be disregarded, every freely falling object near the Earth’s

surface accelerates downward at the same rate, regardless of the mass of

the object.

10

An object in uniform circular motion has a constant speed. For example,

a car going around a circular track at a uniform rate of 90 km/h has a constant

speed. However, the velocity of the object is constantly changing direction.

Since there is a change in velocity, there is an acceleration. Because the

acceleration causes a change in direction that keeps the object in a circular path,

the acceleration is actually perpendicular, or at a right angle to the velocity

vector. This acceleration is called centripetal acceleration. In general, whenever

an object moves in a circle of a radius r with constant speed v, the magnitude of

the centripetal acceleration a

c

is given by the formula:

v

2

a

c

= (v squared divided by r)

r

5 the velocity occurs, the greater the acceleration is. Acceleration is defined as the time rate of change of velocity: change in velocity Í V Acceleration = = time for changing to occur T 8 Since velocity is a vector quantity, acceleration is also a vector quantity. For an object in a straight-line motion, the acceleration may be in the same direction as the velocity or the acceleration may be in the opposite direction of the velocity. In the first instance the acceleration causes the object to speed up and the velocity increases. If the velocity and acceleration are in opposite directions, then the acceleration slows down the object, which is sometimes called a deceleration. 9 There is one very special constant acceleration associated with the acceleration of falling objects: the acceleration of gravity at the Earth’s surface. It is directed downward and is denoted be the letter g. Its magnitude in the SI system is: g = 9.80 m/s2 . The great Italian physicist Galileo Galilei (1564 – 1642) was one of the first scientists to assert that all objects fall downward with the same acceleration. We can state Galileo’s principle as follows: if frictional effects can be disregarded, every freely falling object near the Earth’s surface accelerates downward at the same rate, regardless of the mass of the object. 10 An object in uniform circular motion has a constant speed. For example, a car going around a circular track at a uniform rate of 90 km/h has a constant speed. However, the velocity of the object is constantly changing direction. Since there is a change in velocity, there is an acceleration. Because the acceleration causes a change in direction that keeps the object in a circular path, the acceleration is actually perpendicular, or at a right angle to the velocity vector. This acceleration is called centripetal acceleration. In general, whenever an object moves in a circle of a radius r with constant speed v, the magnitude of the centripetal acceleration ac is given by the formula: v2 ac = (v squared divided by r) r

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