ProjectilesApril 15th 2011

Projectiles •Tiger Tiger Tiger Woods ya'll

•Vancouver 2011

•Fluite Hail Mary Pass

•Thank you Barry Bonds

•Tricycle ride anyone?

What is a projectile?•A projectile is any object that

once projected or dropped continues in motion by its own inertia and is influenced only by the downward force of gravity. (9.81m/s2)

•The path that they follow is called their trajectory.

•The motion of a projectile is described in terms of position, velocity and acceleration.

Different cases of projectiles•An object dropped from rest is a

projectile.(a)•An object that is thrown vertically upward

is a projectile.(b)•An object which is thrown upward at an

angle to the horizontal is a projectile.(c)a. b. c.

Free body diagram.•Since the only force acting on a projectile

is the acceleration due to gravity. The FBD looks like this....

•Lets think of Newton’s laws of motion. Just because the object is Moving upwards, doesNot mean there is an Upward force.

Cannonball example.•If we turned the gravity light switch off

this would happen....

Cannonball example cont. •We flick the gravity light switch back

on....

Non-Horizontally Launched Projectiles.•We will be concerned with object

launched at angles from the horizontal.• The angle will be from the projectile’s launch and the ground.

Horizontal & Vertical Acceleration.•Acceleration due to gravity acts to

influence the vertical motion of the projectile, thus causing a vertical acceleration.

•The horizontal motion of the projectile is the result of the tendency of any object in motion to remain in motion at constant velocity. No horizontal force.

•Due to the absence of horizontal forces, a projectile remains in motion with a constant horizontal velocity.

Check your knowledge.1. Consider these diagrams in answering

the following questions.

Which diagram (if any) might represent ...a. ... the initial horizontal velocity?b. .... the initial vertical velocity?c. . ... the horizontal acceleration?d. . ... the vertical acceleration?e. . ... the net force?

Another example.•2. Supposing a snowmobile is equipped with

a flare launcher that is capable of launching a flare vertically. If the snowmobile is in motion and launches the flare and maintains a constant horizontal velocity after the launch, then where will the flare land?

•a. in front of the snowmobile•b. behind the snowmobile•c. in the snowmobile

Cont.•3. Suppose a rescue airplane drops a relief

package while it is moving with a constant horizontal speed at an elevated height. Assuming that air resistance is negligible, where will the relief package land relative to the plane?

•a. below the plane and behind it.•b. directly below the plane•c. below the plane and ahead of it

Formulas we will be using.•We will be using the kinematic equations

will dealing with projectiles..... Remember?

Homework.•See handout for problems.