Acceleration measures how fast velocity changes. Section 1.3 Acceleration measures how fast velocity changes.

Vocabulary The rate at which velocity changes with time is called _______________. acceleration

Is acceleration a vector? YES – it has both size and direction!

Acceleration Rule #1 Acceleration in the same ___________ as motion. direction

Acceleration Rule #2 Acceleration in the __________ direction of motion. opposite

Acceleration #3 Acceleration at an ____________ to motion. angle

Am I acceleration? a. a car slowing down from 50 miles per hour to 40 miles per hour. b. a car turning a corner. c. a car starting up again after stopping YES! YES! YES!

Thinking Question Suppose velocity remains steady. Will there be any acceleration? Explain. No – acceleration is a change in velocity.

Calculating Acceleration a = v final – v initial t a = acceleration V initial = initial velocity V final = final velocity t = time

Class Problem Mike starts sliding with a velocity of 1 m/s. After 3 seconds, his velocity is 7 m/s. What is his acceleration? a = 7 m/s – 1 m/s 3 s a = 6 m/s 3 s a = 2 m/s2

Practice Problem #1 A man walking at 0.5 m/s accelerates to a velocity of 0.6 m/s in 1 second. What is his acceleration? a = 0.6 m/s – 0.5 m/s 1 s a = 0.1 m/s 1 s a = 0.1 m/s2

Practice Problem #2 A lady accelerates from a stopped position to 6 m/s in 2 seconds. What is her acceleration? a = 6 m/s – 0 m/s 2 s a = 6 m/s 2 s a = 3 m/s2

Bonus Practice Problem A train traveling at 10 m/s slows down to a complete stop in 20 seconds. What is the acceleration of the train? a = 0 m/s – 10 m/s 20 s a = -10 m/s 20 s a = - 0.5 m/s2 What does a negative sign indicate? Negative acceleration, otherwise known as slowing down!

Thinking Question Which scenario demonstrates negative acceleration? a. a bird shifts direction in flight b. an arrow shoots out of a bow c. an out-of-gas car rolls to a stop C – because velocity is decreasing!

Thinking Question Suppose you know the initial velocity of a toy airplane taking off and the final velocity when it is cruising high up in the air. Could you calculate the acceleration? Why or why not? NO – you also need the time interval during which the airplane changed velocity.