Velocity and Acceleration

Velocity and Speed• Velocity and speed are both how fast you are going, but

velocity implies a direction (N, S, E, W) as well

• Four different types of speed

– Instantaneous speed – how fast you are going at a certain point or time.

• example: radar gun

– Average speed – looks at the average speed between two points or times.

• example: driving from Olympia to Seattle

– Constant speed – speed stays the same

• example: cruise control

– Terminal velocity(speed) – the speed at which an object will stop accelerating when dropped

• example: a sky-diver

Math for Velocity/Speed

v = d/t or v = d ÷ t

v = velocityd = distancet = time

5-Step Method to Solving Word Problems

1. Identify what you know (given)

2. Write down the correct formula to use

3. Show your work (“plug and chug” using calculator)

4. Write down answer

5. Make sure answer has a unit of measurement

Example problem

• A bike travels 70 meters in 6.5 seconds. Calculate its velocity.

• A car travels a distance of 100 miles in 2 hours. Calculate its velocity.

d=70m v=d/tt=6.5sec

d=100 miles v=d/tt=2 hours

Given formula show work answer w/ units

10.8 m/sec

50 miles/hour

70m/6.5sec.

100miles/2hours

Acceleration

• a change in velocity (speed or direction)– speeding up or slowing down– changing direction • moving in a circle is always changing

direction

• if acceleration is a negative number it is referred to as negative acceleration or deceleration

Math for Acceleration

a = vvff – v – vii

t

a = accelerationvf = velocity final (speed at the end)vi = velocity initial (speed at the beginning)t = time

Example problem

• A car has an initial velocity of 3.4 m/s. After 3 seconds, its final velocity is 8.2 m/s. Calculate its acceleration.

vi = 3.4m/s a = vf - vi vf = 8.2m/s tt = 3 sec.

Given formula show work answer w/ units

1.6 m/s sec

8.2m/s – 3.4m/s 3 sec