Example Problem:

A car's velocity changes from 0 m/s to 30 m/s 10 seconds later. Calculate the car's average acceleration.

**Velocity and Speed**

**Velocity and Acceleration**

Speed only describes how fast something is moving.

Velocity describes both the speed and direction of an object.

Picture a motorcycle racing down the highway at 100 miles per hour. It meets another motorcycle going 100 miles per hour heading in the opposite direction.

The SPEED of the motorcycles are the same.

The VELOCITY of the motorcycles are different because the motorcycles are not moving in the same direction.

**Acceleration...**

Drag racers idle their engines, the starting signal flashes and the cars leap forward, moving faster and faster until the cars cross the finish line. The drivers release their drag chutes and the cars rapidly slow down and come to a stop.

Speed is not always constant. Like speed, velocity may also change!

Unlike speed, the velocity of an object can change even if the speed of the object remains constant.

Positive Acceleration

Velocity

EXAMPLE:

if a car goes around a curve in the road, its direction changes. Even if the speed remains constant, the velocity changes because the direction of the car changes.

While the car is gaining speed, it is accelerating.

The car is also accelerating while it is slowing down.

What is acceleration?

Acceleration is the rate of change of velocity.

Because velocity includes both speed and direction, if either one changes, velocity will change.

Acceleration can occur through a change in speed or a change in direction.

Acceleration

Negative Acceleration

Velocity

Acceleration

Time Interval

The amount of time that passed while the change in velocity was taking place.

α

Calculating Acceleration

to calculate average acceleration, divide the change in velocity by the time interval.

Change in velocity = final velocity - initial velocity

Be careful when identifying the initial and final velocity. (negative signs indicate negative acceleration) (positive signs indicate positive acceleration)

Remember?

1. What is known?

2. Which equation?

3. Solution?

initial velocity = 0 m/s

final velocity = 30 m/s

time = 10 secs

a = ( 30 m/s - 0 m/s ) / 10 s

a = 30 m/s / 10 s

a = 3 meters / second squared

Whatcha Know Now??

1. One jet plane is flying east at 880 km/h, and another plane is traveling north at 880 km/h. Do they have the same velocities? The same speeds? Explain.

2. A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 secs of the workout. What is the acceleration during this interval?

3. Describe 3 different ways to change your vvelocity when you are riding a bicycle.

Section 3.2: Velocity and Acceleration

DATE!

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NOTES!!

SECTION REVIEW PROBLEMS!

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**:D**