Acceleration

Bell Ringer Sports announcers will occasionally say that a person is accelerating if he/she is moving fast. Why is this not an accurate description of what acceleration is?

Objectives Define acceleration in words and with an equation Identify positive and negative acceleration by analyzing a graph Calculate acceleration with the use of an equation and graph Define and apply the force of gravity

Change in Velocity Each time you take a step you are changing the velocity of your body. You are probably most familiar with the velocity changes of a moving bus or car. The rate at which velocity (speed or direction) changes occur is called acceleration.

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

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

Positive acceleration Negative acceleration

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? Velocity(final) - Velocity(original) Acceleration = time 0 mph - 60 mph = 6 seconds - 60 mph = 6 seconds = - 10 miles per hour per second

Calculate the instantaneous acceleration of the graph: - A constant acceleration produces a straight line or linear slope (rise/run). - The slope of a non-linear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t Calculate the instantaneous acceleration of the graph: a = v/t a = 4m/s / 1s a = 4m/s2

Free fall The constant acceleration of an object moving only under the force of gravity is "g". The acceleration caused by gravity is 10 m/s2 If there was no air, all objects would fall at the same speed Doesn’t depend on mass After 1 second falling at 10 m/s After 2 seconds 20 m/s 3 seconds 30 m/s

Galileo 1600’s Studied how things fell Didn’t have a good clock Rolled balls down an inclined plane Found that the speed increased as it rolled down the ramp

Galileo Acceleration= change in velocity time t = 0 t = 1 second t = 2 seconds t = 3 seconds

Galileo Same things happen when things fall Didn’t drop things from Tower of Pisa

Falling Air resistance will increase as it falls faster An upward force on the object Eventually gravity will balance with air resistance Reaches terminal velocity - highest speed reached by a falling object.

Terminal velocity Force of gravity is constant air resistance increases as you speed up until the force is equal Equal forces, no acceleration constant velocity terminal velocity

Positive Velocity and Positive Acceleration

Positive Velocity and Negative Acceleration

Negative Velocity and Negative Acceleration

Negative Velocity and Positive Acceleration