Change in Velocity You are probably most familiar with the velocity changes of a moving bus or car. Anytime a vehicle is speeding up or slowing down, the velocity is changing. The rate at which velocity (speed or direction) changes is called acceleration.

Acceleration= final velocity- starting velocity Acceleration= final velocity- starting velocity time time Change in velocity = final – starting velocity velocity Change in velocity = final – starting velocity velocity Acceleration= change in velocity Acceleration= change in velocity time time Equations

Acceleration = Velocity (final) - Velocity (original) time A car traveling at 60 mph accelerates to 90 mph in 3 seconds. What is the car’s acceleration? = 90 mph - 60 mph 3 seconds = 30 mph 3 seconds = 10 mph/second

Positive acceleration Negative acceleration Speed Vs. Time Graphs

Acceleration = Velocity (final) - Velocity (original) time A car traveling at 60 mph slams on the breaks to avoid hitting a deer. The car comes to a safe stop 6 seconds after applying the breaks. What is the car’s acceleration? = 0 mph - 60 mph 6 seconds = - 60 mph 6 seconds = - 10 miles per hour per second

- A constant acceleration produces a straight line or linear slope. - A constant acceleration produces a straight line or linear slope. -Remember: slope=Rise/Run - The slope of a non- linear speed-time graph will predict an objects acceleration. a = v/t Speed Vs. Time Graphs

Example What is the acceleration at time= 3 seconds? Acceleration= Speed/Time A= 12 meters per second/ 3 seconds A=4 m/s 2

Gravity Objects in free fall are pulled towards the ground by the force of gravity at a constant rate. Objects in free fall are pulled towards the ground by the force of gravity at a constant rate. The acceleration caused by gravity is constant, pulling downward at 10 m/s 2 The acceleration caused by gravity is constant, pulling downward at 10 m/s 2 If there was no air, all objects would fall at the same speed If there was no air, all objects would fall at the same speed Doesn’t depend on mass Doesn’t depend on mass

Falling Air resistance will increase as an object falls faster Air resistance will increase as an object falls faster Eventually gravity will balance with air resistance Eventually gravity will balance with air resistance At this point, the object reaches terminal velocity -the highest speed reached by a falling object. At this point, the object reaches terminal velocity -the highest speed reached by a falling object.