ACCELERATION Acceleration o Acceleration is change in velocity

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ACCELERATION

ACCELERATION

Acceleration o Acceleration is change in velocity over time. a = vf - vi

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

v vs. t graphs o o Slope = v/t = a What is the

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

Uniform Acceleration l An object speeds up or slows down at a constant rate.

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

Equations using Acceleration o vf = vi + at o d = vit +

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

Working in 2 Dimensions l When we are talking about a car or or

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

Try These l. A car accelerates from 4 m/s to 20 m/s in 4

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

Gravity

Gravity

Gravity l Galileo discovered that by neglecting the effects of air, all objects falling

Gravity l Galileo discovered that by neglecting the effects of air, all objects falling had the same acceleration. l This value is “g” l Or -9. 8 m/s 2 l Different places around the world have different values of g.

g lg is known as the acceleration due to gravity. l Because gravity accelerates

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

How does gravity affect things? l Depends upon your reference point. l If a

How does gravity affect things? l Depends upon your reference point. l If a stone drops from the top of a building: after 1 second it will be traveling -9. 8 m/s downward and after 2 second it will be traveling -19. 6 m/s. l If a ball is thrown upward gravity will slow the ball down and then the ball will accelerate back down. l Time up = time down

Practice l. A brick is dropped from a high scaffold. n What is it’s

Practice l. A brick is dropped from a high scaffold. n What is it’s velocity after 4. 0 s? n How far does the brick fall during this time?

More Practice l. A tennis ball is thrown straight up with an initial speed

More Practice l. A tennis ball is thrown straight up with an initial speed of 22. 5 m/s. It is caught at the same distance above ground. n How high does the ball rise? n How long did the ball remain in the air?

l. A ball is thrown up with an initial velocity of 29. 4 m/s.

l. 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?

l. A stone is dropped from the top of a cliff and hits the

l. 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.

l. A person standing on top of a building throws a ball downward at

l. A person standing on top of a building throws a ball downward at 5 m/s. Find n The velocity it is traveling in 3. 0 s n The distance it travels in 3. 0 s