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.
Acceleration= final velocity- starting velocity time Change in velocity = final – starting velocity velocity Acceleration= change in velocity time
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 brakes to avoid hitting a deer. The car comes to a safe stop 6 seconds after applying the brakes. 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
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
Balloon Racers What will happen if I let go of the blown up balloon? Why did that happen? How can we measure the speed, distance or acceleration of the balloon? A track? Attach the balloon to something?