Projectile Motion – Projectile Motion – Concepts and Concepts and

Horizontal Horizontal ProblemsProblems

Eureka “Acceleration – Part Eureka “Acceleration – Part 1” clip1” clip

What is the “First Rule of What is the “First Rule of Physics”?Physics”?

ANSANS: : Objects tend to keep on Objects tend to keep on doing what they are already doing what they are already doing. Inertia.doing. Inertia.

If you wanted a baseball to travel If you wanted a baseball to travel at 50 km/h, what would you at 50 km/h, what would you need to do in order for it to get need to do in order for it to get to that speed?to that speed?

ANS:ANS: Accelerate it (change Accelerate it (change its speed from 0 to 50 its speed from 0 to 50 km/hr) by applying a forcekm/hr) by applying a force..

Once an object is moving, Once an object is moving, how does the “First Rule of how does the “First Rule of

Physics” apply?Physics” apply?

ANSANS:: It will keep going like that! It will keep going like that! (no force is required). Unless: (no force is required). Unless: friction, air resistance, etc. friction, air resistance, etc. slows it down!slows it down!

The Physics Classroom “ The Physics Classroom “ Parabolic Motion of Parabolic Motion of

Projectiles” simulationProjectiles” simulation If you could turn off If you could turn off

gravity for a bit and gravity for a bit and observe a cannon ball observe a cannon ball that is shot horizontally that is shot horizontally off a cliff, what would off a cliff, what would its motion look like?its motion look like?

ANSANS: A straight line : A straight line at a constant speed. at a constant speed. (It would want to (It would want to keep doing what it is keep doing what it is already doing.)already doing.)

Physclip “Independence of Physclip “Independence of Vertical and Horizontal Vertical and Horizontal

Motion” clip and marble demoMotion” clip and marble demoIf you were to stand on the If you were to stand on the

Sears (I mean, Willis) Sears (I mean, Willis) Tower and shoot a bullet Tower and shoot a bullet horizontally at the same horizontally at the same time you drop another time you drop another bullet straight down, which bullet straight down, which would hit the ground first? would hit the ground first?

ANSANS: SAME TIME: SAME TIME

Horizontal and Vertical Horizontal and Vertical Motions are Motions are IndependentIndependent

Ballistic car demoBallistic car demo

If you got bored of chewing a piece of If you got bored of chewing a piece of bubble gum while driving in your car bubble gum while driving in your car and decided to throw it out the and decided to throw it out the window, straight up into the air, where window, straight up into the air, where would the gum be when it returns back would the gum be when it returns back to the road (in relation to your car)? to the road (in relation to your car)?

ANSANS: The same place the car is : The same place the car is (both continue with the same (both continue with the same horizontalhorizontal speed)speed)

In summary….In summary….

A projectile is any object which once A projectile is any object which once released continues in motion by its released continues in motion by its own own inertiainertia and is influenced only by and is influenced only by the the downwarddownward force of force of gravitygravity..

Projectiles launched horizontally are Projectiles launched horizontally are moving in both the horizontal and moving in both the horizontal and vertical directions, and those vertical directions, and those motions are completely motions are completely independentindependent of one another.of one another.

In summary…..In summary…..

In the horizontal (x) direction, In the horizontal (x) direction, objects travel at a constant objects travel at a constant velocityvelocity

In the vertical (y) direction, objects In the vertical (y) direction, objects accelerateaccelerate at at g = -9.8 m/s/sg = -9.8 m/s/s

Finish Notes on Finish Notes on overhead…overhead…

Still don’t believe me…Still don’t believe me…

Mythbuster -Bullet fired vs. bullet Mythbuster -Bullet fired vs. bullet droppeddropped

https://www.youtube.com/watch?https://www.youtube.com/watch?v=abUBrQmI33Qv=abUBrQmI33Q