VELOCITY & ACCELERATION

VELOCITY*Describes both the speed & direction of an object

VELOCITY Direction*can be expressed using (+) or (-) signs

*up, right or forward are considered to be (+)

*down, left, or backward are considered to be (-)

When can the speed of an object remain constant

while the velocity of the object is changing?

When the object is changing directions!!!!

*the velocity changes

because the direction

changes.

When is the direction of an object always

changing?

*When the object is

turning in a circle.

ACCELERATION

*Rate of change of VELOCITY

ACCELERATION*Occurs when the speed and/or direction of motion changes (Dv)

* during a time interval (Dt)

FORMULA FOR ACCELERATION

*a = Dv / Dt*a = vf - vi / tf - ti

1.) An airplane traveling at a speed of 20 km/min changes to 80 km/min over a distance of 57 km. When the airplane started to speed up it was 1:37 p.m. When the airplane finished its acceleration it was 1:46 p.m. What was the airplane’s acceleration?

Sample problem 1

Need InformationInitial Velocity = 20 km/min Initial Time = 1:37 p.m.Final Velocity = 80 km/min Final Time = 1:46 p.m.

•a = vf - vi / tf - ti

80 km/min - 20 km/min

1:46 - 1:37

a =

60 km/min

9 min

a =

a = 6.67 km/min2

* speeding up is considered to be +

* slowing down is considered to be –

Positive and Negative signs indicate both:

For ACCELERATION…

1.) Direction of Displacement

(Forward/Backward, Left/Right, Up/Down)

2.) Change in Speed(Speeding up, Slowing down)

What is the SIGN of acceleration for a car

speeding up while moving forward?

Speeding up: Positive change in speed

Moving forward: Positive direction of displacement

Positive x Positive =

POSITIVE ACCELERATION

Sample Problem 2

What is the SIGN of acceleration for a car that

is speeding up while moving backwards?

Speeding up: Positive change in speed

Moving backwards: Negative direction of displacement

Positive x Negative =

NEGATIVE ACCELERATION

Sample Problem 3

What is the SIGN of acceleration for a car slowing down while moving backwards?

Slowing down: Negative change in speed

Moving backwards: Negative direction of displacement

Negative x Negative =

POSITIVE ACCELERATION

Sample Problem 4

Negative Acceleration is

NOT the same as Deceleration !!!!

DECELERATION Refers ONLY to the slowing

down of an object

The last sample problem

demonstrated a positive acceleration

sign that included deceleration

Acceleration of Coach McKnight on the Interstate

SPEED

(M/S)

T I M E (SEC.)

“To calculate total distance covered you must color in the graph.”

Acceleration of Coach McKnight on the Interstate

T I M E (SEC.)

SPEED

(M/S)

“To calculate total distance covered you must color in the graph.”