Projectile motion Chapter 4, Section 4 Lecture 08

Projectile motionChapter 4, Section 4

Lecture 08

General Physics (PHYS101)

2

Lightning Review: 2D and 3D motion

•Displacement

•Velocity

•Acceleration

Projectile motion

• A projectile is an object that is thrown in air and moves only under the influence of Earth’s gravity.

• An object moves in both x and y directions simultaneously, so that we deal with a two dimensional motion. • We will ignore air friction

• No acceleration in the horizontal direction

• The projectile’s acceleration is the free-fall acceleration

Equations of motion

The horizontal motion The vertical motion

Equation for the trajectory

Parabola!

Projectile Motion: displacement

•At any time t, the projectile’s horizontal and vertical displacement:

•The magnitude of the displacement:

Projectile Motion: velocity

The maximum height of projectile

•The highest height which the object will reach is known as the peak of the object's motion.

•The increase of the height will last, until , that is,

•Time to reach the maximum height:

•From the vertical displacement of the maximum height of the object

The maximum distance of projectile

•From the horizontal displacement of the maximum distance of projectile:

•The horizontal range d of the projectile is the horizontal distance the projectile has travelled when it returns to its initial height (y=0).

•Time to reach the ground:

•Note that R has its maximum value when

Examples of projectile motion

•An object may be thrown horizontally

•The initial velocity is all in the x-direction

•All the general rules of projectile motion apply

Projectile motion vs free fall

Examples of projectile motion

•Follow the general rules for projectile motion

•Break the y-direction into parts•up and down•symmetrical back to

initial height and then the rest of the heigh

What do you think?1. Hits the monkey regardless of the value of v0.2. Hits the monkey only if v0 is large enough.3. Misses the target.

The downward acceleration of the bullet and the monkey are identical, so the bullet hit the target - they both fall the same distance.