Gravity  Does gravity ever turn off?  Does gravity affect everything in the same way?  Why does the book hit before the paper? NO YES! Air Resistance slows down the paper- but that doesn’t change the fact that gravity is still pulling it down.  If I throw a ball into the air, is gravity affecting it? YES. My hand speeds the ball up, but as soon as it leaves my hand, it begins to slow down.  When the ball reaches it’s highest point, it briefly comes to a stop before changing direction. zero What is it’s velocity? Is it accelerating? Yes! Gravity!

Acceleration Units acceleration= velocity = distance/timetime SI units = m/s/s = m s 2

Acceleration direction  (+) means forward/up,  (-) means backward/down +v +a -v -a +v -a -v +a Forward, speeding up Backward, speeding up Forward, slowing down Backward, slowing down

Thinking Questions  If a ball falls off of a shelf and you calculate the velocity right before it hits the floor, will the velocity be + or -? NEGATIVE… moving down

Thinking Questions  If you toss a ball in the air, is it’s initial velocity + or -? Positive… moving up

Thinking Questions  If you toss a ball in the air, as it rises, will it’s acceleration be + or -? NEGATIVE… moving upward, but slowing

GRAVITY g (on earth) = m/s 2

Kinematics Equations: EquationFor use when you know/need: Unknown: a = v f - v i Δt a = v f 2 - v i 2 2(Δd) Δd = v i t + at a v i v f t a v i v f d a v i d t d t vfvf