Motion in 2DChapter 6

6.1 Projectile Motion• Projectile – object shot, launched, kicked,

thrown, etc through the air• Path is up then down in curve

– Called trajectory• Forces?

– Force of earth and air resistance– Initial force causing motion

• When known, can calculate trajectory

Independence of Motion in 2D• Objects fall at the same

rate– Dropped compared to

launched (vertically)– Myth Busters clip

• Can separate motion– Motion in x-direction and

motion in y-direction– Independent of each other

Launched at Angle• Symmetric

• Range

• Flight time or Hang time

6.2 Circular Motion• Change in direction

leads to acceleration

• Uniform Circular Motion– Constant speed around

circle with fixed radius– Position vector length

doesn’t change

Centripetal Acceleration• Velocity direction

changes, but length is constant– Tangential to circle

• Acceleration points in same direction as velocity change

• Centripetal means center seeking

Centripetal Acceleration• Pg 154 - derivation

• Period – time needed for object to make a complete revolution

• Newton’s Second form – Net force always points toward center of circle– Net centripetal force

“Centrifugal Force”• Centrifugal – outward force

– Nonexistent– Fictitious– Actually inertia described by Newton’s 1st Law

6.3 Relative Velocity• Albert Einstein and his Theory of Relativity

• Motion relative to a moving object and seen by stationary observer– Vice versa

Lab• Catapult lab

– http://teachingphysics.wordpress.com/2009/03/01/projectile-motion-activity/