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Acceleration

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.

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Acceleration

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  1. Acceleration

  2. 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.

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

  4. 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

  5. Positive acceleration Negative acceleration

  6. 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

  7. - 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

  8. 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

  9. 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

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

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

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

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

  14. 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.

  15. 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

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