Projectile Motion – Concepts and Horizontal Problems

Eureka “Acceleration – Part 1” clip Eureka “Acceleration – Part 1” clip What is the “First Rule of Physics”? ANS: Objects tend to keep on doing what they are already doing. Inertia.

If you wanted a baseball to travel at 50 km/h, what would you need to do in order for it to get to that speed? ANS: Accelerate it (change its speed from 0 to 50 km/hr) by applying a force.

Once an object is moving, how does the “First Rule of Physics” apply? ANS: It will keep going like that! (no force is required). Unless: friction, air resistance, etc. slows it down!

The Physics Classroom “ Parabolic Motion of Projectiles” simulation The Physics Classroom “ Parabolic Motion of Projectiles” simulation If you could turn off gravity for a bit and observe a cannon ball that is shot horizontally off a cliff, what would its motion look like? If you could turn off gravity for a bit and observe a cannon ball that is shot horizontally off a cliff, what would its motion look like? ANS: A straight line at a constant speed. (It would want to keep doing what it is already doing.) ANS: A straight line at a constant speed. (It would want to keep doing what it is already doing.)

Physclip “Independence of Vertical and Horizontal Motion” clip and marble demo Physclip “Independence of Vertical and Horizontal Motion” clip and marble demo If you were to stand on the Sears (I mean, Willis) Tower and shoot a bullet horizontally at the same time you drop another bullet straight down, which would hit the ground first? ANS: SAME TIME Horizontal and Vertical Motions are Independent

Ballistic car demo Ballistic car demo If you got bored of chewing a piece of bubble gum while driving in your car and decided to throw it out the window, straight up into the air, where would the gum be when it returns back to the road (in relation to your car)? If you got bored of chewing a piece of bubble gum while driving in your car and decided to throw it out the window, straight up into the air, where would the gum be when it returns back to the road (in relation to your car)? ANS: The same place the car is (both continue with the same horizontal speed) ANS: The same place the car is (both continue with the same horizontal speed)

In summary…. A projectile is any object which once released continues in motion by its own inertia and is influenced only by the downward force of gravity. A projectile is any object which once released continues in motion by its own inertia and is influenced only by the downward force of gravity. Projectiles launched horizontally are moving in both the horizontal and vertical directions, and those motions are completely independent of one another. Projectiles launched horizontally are moving in both the horizontal and vertical directions, and those motions are completely independent of one another.

In summary….. In the horizontal (x) direction, objects travel at a constant velocity In the horizontal (x) direction, objects travel at a constant velocity In the vertical (y) direction, objects accelerate at g = -9.8 m/s/s In the vertical (y) direction, objects accelerate at g = -9.8 m/s/s

Finish Notes on overhead…

Still don’t believe me… Mythbuster -Bullet fired vs. bullet dropped Mythbuster -Bullet fired vs. bullet dropped I33Q I33Q I33Q I33Q