Warm Up 1. Describe the motion of the person. 2. Find the velocity of the person at each interval.

Warm Up 1. Describe the motion of the person. Stands still, moves away, stands still, moves toward 1. Find the velocity of the person at each interval. 0 m/s, 0.4 m/s, 0 m/s, 0.25 m/s

Change in Velocity  Initial Velocity (v i ) – An object’s velocity when you start measuring acceleration  Final Velocity (v f ) – An object’s velocity when you finish measuring acceleration Δv = v f - v i

Acceleration

Quick Checks What is acceleration? Is there acceleration in these situations? Why? a) A car stopping at a red light b) A car using cruise control on the freeway. c) A pendulum d) Dropping an egg – Answers on next click

Quick Checks What is acceleration? Is there acceleration in these situations? Why? a) A car stopping at a red light b) A car using cruise control on the freeway. c) A pendulum d) Dropping an egg

Acceleration  Acceleration is not just a change in velocity, it’s how fast that change happens.

Units for Acceleration

Acceleration  Positive acceleration = speeding up  Negative acceleration = slowing down

Practice – Ex 1  A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?

Use GUESS! G: v f = 26 m/s v i = 10 m/s ∆t = 2 s U: acceleration E: acceleration = ∆v/∆t S: a = 26m/s – 10m/s 2 s S: a = 16m/s 2s a = 8m/s/s or 8m/s 2 A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?

Quick Checks 1. A car travels in a straight line at 60 mi/hr. A. Is the car accelerating? B. What is the car’s acceleration? 2. A car goes from 0 mph to 60 mph in 6 seconds. A. Is the car accelerating? B. What is the car’s acceleration? Answers on next slide

Quick Checks 1. A car travels in a straight line at 60 mi/hr. A. Is the car accelerating? No B. What is the car’s acceleration?0 m/s 2 2. A car goes from 0 mph to 60 mph in 6 seconds. A. Is the car accelerating? Yes B. What is the car’s acceleration? (60 – 0 mph)/6 s = 60 mph/6s = 10 miles /hr · s

Practice Problems- Use GUESS a) While traveling along a highway a driver slows from 25 m/s to 15 m/s in 12 seconds. What is the automobile’s acceleration? (Remember that a negative value indicates a slowing down or deceleration.) b) While hunting a gazelle, a lion starts from rest, and speeds up to 20 m/s in 4.2 seconds. What is the acceleration of the lion?

Example 2  If a Ferrari, with an initial velocity of 10 m/s, accelerates at a rate of 50 m/s 2 for 3 seconds, what would its final velocity be?

Practice – Use GUESS  In a car accident, a driver hits the brakes to decelerate at 3 m/s 2 in 2 seconds. What speed was the car going before the accident, assuming it comes to a complete stop?  G: a = -3 m/s 2 t = 2 sec v f = 0 m/s

Homework  Speed, Velocity, Acceleration Work Sheet

Exit Question  What is the final velocity of a car that starts at 10 m/s, then accelerates at 5 m/s/s for 10 seconds?  USE GUESS!!