Projectile Motion

Instructional Objectives: Students will be able to: –Define Projectile Motion –Distinguish between the different types of projectile motion –Understand and describe accelerated motion in 2 Dimensions using projectile motion –Apply the concept to a toy catapult and measure its velocity

Projectiles launched at an angle StartStop

Projectile motion is a combination of horizontal motion and vertical motion. The horizontal motion of a projectile is constant because no gravitational force acts horizontally

The vertical motion of a projectile is nothing more than free fall with a constant downward acceleration due to gravity.

A projectile moves horizontally with constant velocity while being accelerated vertically. The result is a motion in a curved path.

Factors Affecting Projectile Motion What two factors would affect projectile motion? –Angle –Initial velocity Initial Velocity Angle

Projectiles launched at different angles.

Projectiles launched at an angle vivi ΔyΔy v yf ΔxΔx θ StartStop vyvxvyvx vxvyvxvy

Projectiles launched at an angle Δx = v i (cos  )Δt (horizontal distance) v yf = v i (sin  ) + gΔt  (final vertical velocity) v yf 2 = v i 2 (sin  ) 2 + 2gΔy (final vertical velocity) Δy = v i (sin  )Δt + ½ gΔt 2  (vertical distance)  if you are finding time with either of these two formulas, you are only covering half of the parabola

In Conclusion A projectile is any object upon which the only force is gravity. Projectiles travel with a parabolic trajectory due to the influence of gravity. There are no horizontal forces acting upon projectiles and thus no horizontal acceleration. The horizontal velocity of a projectile is constant. there is a vertical acceleration caused by gravity (9.8 m/s. The horizontal motion of a projectile is independent of its vertical motion.

Test your knowledge Suppose a snowmobile is equipped with a flare launcher which is capable of launching a sphere 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 (neglect air resistance)?

Test your knowledge Suppose an airplane drops a flare while it is moving at constant horizontal speed at an elevated height. Assuming that air resistance is negligible, where will the flare land relative to the plane? A. Directly below the plane. B. Below the plane and ahead of it. C. Below plane and behind it.

Why does the horizontal component of a projectile’s motion remain constant? Because no force acts on it horizontally.

Why does the vertical component of a projectile’s motion undergo change? Because gravity is pulling it downward.

How does the vertical distance a projectile falls below an otherwise straight-line path compare with the vertical distance it would fall from rest in the same time? The vertical and horizontal distances are equal.

A projectile is launched vertically at 100 m/s. If air resistance can be neglected, at what speed does it return to its initial level? 100 m/s

There is an interesting monkey down at the zoo. The monkey spends most of its day hanging from a limb of a tree. The zookeeper feeds the monkey by shooting bananas from a banana cannon to the monkey in the tree. This particular monkey has a habit of dropping from the tree the moment that the banana leaves the muzzle of the cannon. The zookeeper is faced with the dilemma of where to aim the banana cannon in order to hit the monkey. If the monkey lets go of the tree the moment that the banana is fired, then where should she aim the banana cannon?

To ponder this dilemma consider the following: Shoot at the monkey in a gravity free environment. In the absence of gravity, the banana moves in a straight line path (and does not experience any downward acceleration) and the monkey does not fall once he lets go of the tree.

Shoot at the monkey with gravity. The banana moves in a parabolic path in the presence of gravity. In the presence of gravity, the monkey also accelerates downward once he lets go of the limb. Both banana and monkey experience the same acceleration since gravity causes all objects to accelerate at the same rate regardless of their mass. Since both banana and monkey experience the same acceleration each will fall equal amounts. The banana misses the monkey, moving over his head as it was originally aimed.

Shoot at the Monkey at a Fast Speed with Gravity On Since the banana left the muzzle moving very fast, the banana reaches the monkey before the monkey has fallen very far.

Shoot at the Monkey at a Fast Speed with Gravity On Since the banana left the muzzle moving very slow, the banana reaches the monkey after the monkey has fallen considerably far. In conclusion, the key to the zookeeper's dilemma is to aim directly at the monkey.

A projectile was launched at an angle of 22.0 o with an initial velocity of 25.0 m/s. a. How high will it go?

b. How long will it take to reach the top of the flight?

c. How long did it take the projectile to land?

d. How far down the field did the projectile travel?