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ACCELERATION

Learn about the fundamentals of acceleration, including its definition, calculation, and application in 2 dimensions. Explore the main kinematics equations and discover how gravity affects objects in motion. Get hands-on practice with various acceleration problems and improve your understanding of this fundamental concept in physics.

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ACCELERATION

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  1. ACCELERATION

  2. Acceleration • Acceleration is change in velocity over time. • a = vf - vi t • If vf > vi, a is +……this is acceleration • If vf < vi, a is -……this is deceleration or (-)acceleration

  3. v vs. t graphs • Slope = v/t = a • What is the average acceleration over the first 40s? • Area under the curve gives displacement • v x t = m/s x s = m • How far did the object travel in 40s?

  4. Uniform Acceleration • An object speeds up or slows down at a constant rate. • Displacement depends upon initial velocity, acceleration, and time. • Final velocity depends on initial velocity, acceleration and time. • To solve for these unknowns, we use the 3 main Kinematics Equations

  5. Equations using Acceleration • vf = vi + at • d = vit + 1/2at2 • vf2 = vi2 + 2ad • Be sure to use the equation that you have the most known information for and includes the variable you are looking for.

  6. Working in 2 Dimensions • When we are talking about a car or or other object traveling on the ground, we are working on the horizontal plane. • We can also use these equations in a vertical plane. • In a vertical plane, acceleration is due to gravity. More to come later.

  7. Try These • A car accelerates from 4m/s to 20m/s in 4s. What is the acceleration? • A car starts from rest accelerates 5m/s2 over 30m. What is the final velocity of the car? • A car slows from 40m/s to a stop in 5s. What is the acceleration? • If an object starts from rest and accelerates 10m/s2 for 2s. How far will it travel?

  8. Gravity

  9. Gravity • Galileo discovered that by neglecting the effects of air, all objects falling had the same acceleration. • This value is “g” • Or -9.8m/s2 • Different places around the world have different values of g.

  10. g • g is known as the acceleration due to gravity. • Because gravity accelerates objects in a downward direction, g is a negative acceleration. • This is due to the fact that acceleration is a vector. • GLOC

  11. How does gravity affect things? • Depends upon your reference point. • If a stone drops from the top of a building: after 1 second it will be traveling -9.8m/s downward and after 2 second it will be traveling -19.6 m/s. • If a ball is thrown upward gravity will slow the ball down and then the ball will accelerate back down. • Time up = time down

  12. Practice • A brick is dropped from a high scaffold. • What is it’s velocity after 4.0s? • How far does the brick fall during this time?

  13. More Practice • A tennis ball is thrown straight up with an initial speed of 22.5m/s. It is caught at the same distance above ground. • How high does the ball rise? • How long did the ball remain in the air?

  14. A ball is thrown up with an initial velocity of 29.4 m/s. How much time does it take for the ball to stop rising?

  15. A stone is dropped from the top of a cliff and hits the ground 3 seconds later. Find a) the magnitude of the velocity at which the stone hit the ground b) the distance that it fell.

  16. A person standing on top of a building throws a ball downward at 5m/s. Find • The velocity it is traveling in 3.0s • The distance it travels in 3.0s

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