Speed and velocity

Objectives• Describe one dimensional

motion using equations for speed and velocity.

• Analyze one dimensional motion using equations for speed and velocity.

• Define and identify positive and negative velocities.

Terms• Speed• Velocity

Equations

• ____________________ is the distance traveled divided by the time taken.

• V __________________• d __________________ • t ___________________

• ____________________ is the change in position divided by the change in time.

• V ___________________• change in

____________________ • change in

________________

Rearranging Formulas Speed

𝑉=𝑑𝑡

• Solve for distance • Solve for time

Rearranging Formulas Velocity

• Solve for change in position

• Solve for change in time

• Solve for initial position

• Solve for final position

Speed vs. Velocity•Are speed & velocity just two different words for the same thing?• In everyday life you probably use these words

interchangeably.

• In Physics class, speed and velocity are related, but NOT exactly the same.

Using The Speed Equation1. A car travels 30 meters in a trip that

lasts 2.0 seconds. What is the car’s speed?

2. If you go a distance of 45 meters at a speed of 16 m/s, how long does this trip last?

3. A fox runs at a speed of 9.7 m/s for 12 seconds. How far does the fox run?

How fast is fast?See if you can come up with an example of when an actual object might move at each speed.

1) 0.1 m/s

2) 1 m/s

3) 10 m/s

4) 100 m/s

5) 1000 m/s

• Distance is always ____________________.

• Time is always ____________________.

• Therefore, speed is always ____________________ !

Speed is scalar

• So how do we tell the difference between moving backward and forward?

• We need a new variable: ____________________!

Velocity is defined as the ____________________ in ____________________ divided by the ____________________ in _______________.

Reminder: Δ means“the ____________________.”

Velocity

A change in position, Δx, can be positive or negative.

That means that velocity can be ____________________ or ____________________.

Velocity & Direction• ____________________ Velocity implies object is traveling: ____________________ or right/East

• ____________________ Velocity implies object is traveling: down/South or ____________________

-

+Up

Down

North

South

+-Left - Right

West - East

Velocity can have ____________________ or ____________________ values.

The ____________________ of the velocity tells you the ____________________ of motion.

Velocity is a ____________________. A vector is a type of variable which includes directional information in a mathematically useful way.

Velocity is a vector

Using the Velocity Equation• A car starts at 30m and finishes

at 10m in a trip that takes 2.0 seconds.

• What is the change in position?

• What is the car’s velocity?

Using the Velocity Equation• A car travels at 15m/s. Four

seconds after starting out, it is at a position of 40m.

• What is the car’s change in position?

• Where did the car start from?

Finding Change in Position• Quick reminders:

• stands for ____________________• Subscript “i” means “____________________”• Subscript “f” means “____________________”

• Example: If a boy walks from a starting position of 3.2m to an ending position of 7.1, what is the boy’s change in position?

Finding Velocity• If a boy walks from a starting position of 3.2m to an ending

position of 7.1 in 2 seconds, what is his velocity?

Finding Velocity• If a boy walks from a starting position of 7.1m to an ending

position of 3.2m in 2 seconds, what is his velocity?

Positions & Velocities Part 1• Can there be a positive position and a negative velocity?

+-

Positions & Velocities Part 2• Can there be a negative position and a positive velocity?

+-

Positions & Velocities Part 3• Can there be a negative position and a negative velocity?

+-

Positions & Velocities Part 4• Can there be a positive position and a positive velocity?

+-

1. A swallow moves 80 meters east in 5 seconds. 0

What is its speed?

What is its velocity?

How can the two be different?

Assessment

2. Write an English sentence that means the same as this equation:

Assessment

3. Give an example of an object with positive position and negative velocity.

Assessment