Today I will describe the path of a projectile.

Warm Up – What does the path of a projectile look like at different angle?

Think/Pair/Share!

Physics

Chapter Overview1. Projectiles in general2. Horizontal Projectiles (2 types)3. Projectiles at an angle

Free Fall◦When an object moves through the air with ONLY gravity acting on it

Gravity◦A downward pull on an object toward the Earth (this pull causes objects to accelerate at a rate of -10 m/s2)

Projectile◦Any object in free fall (remember in free fall object can be moving up or down)

◦ The free fall objects we discussed before were projectiles!

The motion in these examples is all vertical (y)

Projectiles can also have motion in 2d Vertical and horizontal (x and y)

◦ 2d projectiles follow a parabolic path

Horizontal and Vertical Motion are Completely Independent of Each Other!!!

In crossing a river (x), does giving a boat a current (y), affect how long it takes to get across (x)?

We already know everything about the “Y”!! It’s just free fall!!

Acceleration

What causes an object to accelerate in the vertical?

Gravity! (a = -9.8m/s2 )

In the y direction, the acceleration is ALWAYS -9.8 m/s2!

◦ At the objects highest point its vy = 0 ; not moving upward or downward

◦ What does velocity look like in the y direction for the rest of the path?

First Half –Up - positive direction Slowing down

Second Half -Down - negative directionSpeeding up

◦ What about distance and displacement?

◦ How high up does the projectile rise?

◦ We know how to calculate that!!

◦ What about time?

The time it takes for the projectile to go from bottom to the top is the same as the time it takes to go from the top to the bottom!

The movement in the x (horizontal direction)

Gravity DOES NOT act on the horizontal since it only acts downward

There is nothing else (like a motor) giving the projectile acceleration in the x.

◦ This means that acceleration in the x direction is always zero!

Since the object will not accelerate in the horizontal direction…

◦ This means velocity in the x-direction is always CONSTANT!!!! Vi = Vf

What does horizontal velocity look like…

I thought this was zero?Oh right, that’s in the y!

All velocities in the x will be equal –including direction!

What does distance and displacement look like in the x?

How far it travels along the ground.

The vertical and horizontal components are independent of one another

Time is the link between the components◦ The time of the flight is the same for the x and the y

**All of this assumes no air resistance.

◦ Air resistance can have a large or small effect depending on the object.