Acceleration

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

- 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

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

A final velocity can be calculated over a vertical displacement “dy" during free fall using the equation: v2final = 2gdy

The vertical displacement “dy" that occurs during a specific time of free fall can be determined using the equation: dy = 1/2 gt2 Or a time interval can also be determined over a specified distance of freefall using the equation: t2 = 2dy /g

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