Acceleration

March 2, 2010

Objectives1. Define acceleration and deceleration

2. Describe the relationship between velocity and acceleration

3. Calculate acceleration

Speed vs Velocity?

Speed – how fast an object is changing its position

Velocity – an object’s speed and direction

Velocities can be combined.

Rowing downstream at 16 km/h southeast on a river which is moving 10 km/h southeast

results in a total velocity of 26 km/h southeast.

Rockets are launched in the same direction as the earth rotates.

Added boost of 1800 km/h!

Acceleration

the rate of change in velocity

final velocity – initial velocity time

Acceleration

A = Vf – Vi

T

Acceleration equation

A = V T

is

pronounced delta

Acceleration unitskm / h /h or km / h2

m/s/s m / s2

km / h /s

kilometers per hour per hour

meters per second per second

kilometers per hour per second

Example problem

A roller coaster’s speed at the top of a hill is 10 m/s. Two seconds later, it reaches the bottom of the hill with a speed of 26 m/s. What is the acceleration of the roller coaster?

Vi

Vf

t

A = V T

Acceleration equation

A = V T

Final velocity = 26 m/s Initial velocity = 10 m/s Time = 2 s

A = 26 m/s – 10 m/s = 16 m/s = 8 m/s/s

2s 2s

Deceleration

Negative acceleration

Example Problem At the end of a race,

a bicycle is decelerated from a velocity of 12 m/s to a rest position in 30 seconds. What is the deceleration of this bicycle?

Vi

Vf t

Final velocity = 0 m/s

Initial velocity = 12 m/s

Time = 30 s

A = V T

Acceleration equation

A = V T

Final velocity = 0 m/s Initial velocity = 12 m/s Time = 30 s

A = 0 m/s – 12 m/s = -12 m/s = -0.4 m/s/s

30s 30s

If a rocket in space is moving at a constant velocity of 9.8 m/s and then uses its propulsion system to accelerate to 12.0 m/s during a 3.0 minute burn, what would be the acceleration of the rocket?

A = Vf – Vi

t

If a rocket in space is moving at a constant velocity of 9.8 m/s and then uses its propulsion system to accelerate to 12.0 m/s during a 3.0 minute burn, what would be the acceleration of the rocket?

A = Vf – 9.8 m/s

t

If a rocket in space is moving at a constant velocity of 9.8 m/s and then uses its propulsion system to accelerate to 12.0 m/s during a 3.0 minute burn, what would be the acceleration of the rocket?

A = 12.0 m/s – 9.8 m/s

t

If a rocket in space is moving at a constant velocity of 9.8 m/s and then uses its propulsion system to accelerate to 12.0 m/s during a 3.0 minute burn, what would be the acceleration of the rocket?

A = 12.0 m/s – 9.8 m/s

3 min

A = 0.73 m/s/min