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Ch 7 Sec 2
Projectile Motion
Chapter 7: Projectile Motion
Look, up in the sky…!
A PROJECTILE- is an object that moves
through the air under the influence of gravity
ONLY (ignoring air resistance).
The path of a PROJECTILE is a curve
through space called the TRAJECTORY of
the projectile.
Trajectory depends on initial thrust force as
well as gravity.
Motion in 2 Dimensions
In throwing (horizontally) a ball and
dropping another ball (vertically) at the
same time, it is found that the horizontal
motion effects RANGE but DOES NOT
effect vertical motion…
Why not?
Vertical motion is changed because
gravity acts on an object. (Moving
horizontally or NOT!) Gravity only acts
Projectile Motion
So what?
Since the earth does not change when a
ball is thrown horizontally or dropped
vertically, the vertical positions each time
interval of EACH ball will be the same!
According to Newton’s First Law of Motion,
the thrown object will cover the same
horizontal distance or velocity each
second as the second before. No other
force acts horizontally on it.
What do you think?
If you throw a water balloon horizontally, will it hit the
ground sooner than dropping it from the same
height?
How about a bullet shot and one dropped at the
same time? Range, more! Time, SAME!
Projectile Vectors
Read pg 156.
Look at Diagrams 7-6 a and b.
Combining vectors of constant horizontal velocity with uniform vertical acceleration gives the trajectory (path) a curve called a PARABOLA.
Resultant vectors are TANGENT to the curve of the parabola. They represent the instantaneous velocity of the projectile.
Projectiles Launched Horizontally
Throwing a ball horizontally, there is NO
initial VERTICAL velocity, so the velocity
downward is the same as if it were at rest
initially.
Its vertical motion matches a ball dropped at
the same time.
See picture pg. 155 Figure 7-5
Review Example Problem pg 157.
Do pg 158 #s 9-11 & p. 172 #s 39-41.
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