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.