Physics LabPhysics LabAgenda – Thursday 12/16/04

– Pick-up materials on front desks– Intro to Horizontal Motion Lab– Bring physics HW to do in class

Physics Physics

Agenda Thursday 12/16/04– Return Plane Labs– Horizontal Motion – HW: Read p. 155-157 and probs. p. 170 #8, 9, 22

Projectile MotionProjectile Motion

A projectile can be anything that moves though the air after it has been given an initial “thrust” or input force

Projectiles are only under one force as they move through the air –GRAVITY!

We ignore air resistance in most cases to simply the problems

There are two general categories– Projectiles launched horizontally– Projectiles launched at an angle

Projectile MotionProjectile Motion Bullet Demonstration Ballistics Cart Demo

Important Concepts

1. Vertical and horizontal motions are independent of each other

2. We can relate the height, time in the air, and initial vertical velocity of the projectile by using its vertical motion, then determine the range (x-distance)

3. We use basic motion equations to solve!

What do You Notice??What do You Notice??

Projectiles Launched HorizontallyProjectiles Launched Horizontally

A cat is tossed horizontally at 20 m/s off a cliff that is 50 m high.

a) How long is the cat in the air?

b) How far from the base of the cliff does the cat land?

c) How fast is the cat moving the Instant before it splats on the ground?

Problems Solving StrategyProblems Solving Strategy1. Write known and unknown variables2. Write variables for x and y directions

yi = 0

yf = -50 mxi = 0 xf = ?

vyi = 0

vyf = ?

vxi = 20 m/s

vxf = 20 m/sWHY?

vnetf = ?

t = ?

ay = g = -9.8m/s2

ax = 0

What’s missing?

Practice Problem #2Practice Problem #2

A plane that is moving 200 m/s drops a package. The package takes 15 seconds to reach the ground.– A) What height was the package dropped from?– B) How far did the plane travel from the time the

package was released until the package hit the ground? Is this the same distance the package travels?

– C) How fast was the package moving when it hit the ground?

End

Regents PhysicsRegents PhysicsAgenda – Projectile Motion:

– Projectiles at any angle

HW: problems p. 160 #12,13

problems p. 172 #42, 47 (tricky)

Review ProblemReview ProblemA plane that is moving 225 m/s drops a

package. The package takes 10 seconds to reach the ground.– A) What height was the package dropped from?– B) What horizontal distance did the package cover

after it was dropped from the plane?– C) How fast was the package moving when it hit the ground?

Projectiles at Any Angle..Projectiles at Any Angle..a few a few differencesdifferences

When projectiles are launched at any angle, the initial velocity has both horizontal and vertical components

This means that Vo must be used, not just

Vxi … we’ve done this before!

Vxi = Vocos

Vyi = Vosin

Variables of MotionVariables of Motion

Other differences and similaritiesOther differences and similarities

Time in air is called flight time and ½ of flight time occurs at ½ range

So..it takes the same amount of time to go up as it does to fall down

At ymax, Vyf = 0m/s

Still, only force acting on the is gravityStill, no acceleration in the x direction!

Practice ProblemPractice ProblemA football is thrown with an initial velocity of 5.5 m/s at an angle of 49 above the horizontal.

1. How long did it take the ball to return to the launching height?2. What was the maximum height the ball attained?3. What was its range?

range

Max height

Vyf = 0 m/s

Let’s Play GolfLet’s Play Golf

Regents PhysicsRegents Physics

Agenda Review HW Problems and LabCircular MotionHW: Read p. 163-168

Problems p. 166 #14-16

Circular MotionCircular Motion

Question: Can an object be accelerated if its speed remains constant?

What’s uniform circular motion?

It is the movement of an object or point mass at constant speed around a circle with a fixedradius

Circular MotionCircular Motion

Demo