Average Velocity

Average Velocity

2.2

Open Ended

Explain the difference between distance and displacement in your own words.

Position, Distance, Displacement

• The location of an object in a frame of reference is called position.

• The length traveled by an object moving in any direction or even changing direction is called distance.

• The separation between original and final position is called displacement.

Open Ended

Example: In stock car races, drivers often travel 500 miles or more, but their final displacement is only a few feet. Why?

Motion is relative

• Everything moves.  Even things that appear to be at rest move. 

•  Motion is described by motion relative to something else. Relative to the sun, the center of the galaxy, etc.b. We will discuss motion (things in our environment) relative to the surface of the Earth.

Multiple Choice

What is Relative?

• Relative means opposite

• Relative means in comparison of something else

Speed

• Speed is measure of how fast something is moving (rate at which distance is covered)

•  Rate– term used to describe something divided by time.

• Speed = Units of distance / units of time (distance covered per unit of time)

Multiple Choice

Which of the following is a unit of time?

• sec
• mi
• m/s
• km

Common Units

• miles/hour (mi/h)

•  kilometers/hour (km/h)

• meters/second (m/s) Used in physics

Multiple Choice

Which of the following is a unit of speed ?

• sec
• mi
• m/s
• min

Speed

Instantaneous Speed– the speed at any instant (What you see on a car’s speedometer)

Average Speed

• Average Speed– total distance covered/time interval

• Does not indicate variations in speed over time.

• still describes rate at which distance traveled

Multiple Choice

What two measurements are needed to calculate average speed?

• Distance and Time

• Volume and Mass

• Mass and Time

• Speed and Distance

Multiple Choice

What is the difference between instantaneous speed and average speed?

• Average speed happens in a particular instant, Instantaneous speed is the speed of an object over a longer period of time.
• Instantaneous speed is never right, average speed is always right
• Instantaneous speed happens in a particular instant, Average speed is the speed of an object over a longer period of time.
• Do not pick this answer

Multiple Choice

What is the formula for average speed?

• Average Speed = Total Time $\div$ Total Distance

• Average Speed = Total Time + Total Distance

• Average Speed = Total Distance $\div$ Total Time

• Average Speed = Total Distance $\times$ Total Time

Velocity

• In ordinary language, the words speed and velocity both refer to how fast an object is moving, and are often used interchangeably.

• Speed is the magnitude of an object's motion, with no regard for the direction.

• Velocity is the measure of both speed and direction of motion.

Multiple Choice

What is speed?

• how far you go
• how much distance is covered over a period of time
• how fast you accelerate
• the change in the location of a object

Multiple Choice

What is velocity?

• the quickness of an object
• the location of an object
• acceleration
• speed in a specific direction

• Velocity is speed in a given direction.

• Speed is how fast an object moves (direction does not) matter.

Constant Velocity– must have constant speed and direction

• Object moves in straight line

• Object’s path does not curve

Multiple Choice

Total distance divided by total time is

• average speed
• constant speed
• instantaneous speed
• acceleration

Multiple Choice

What arguments do you need to compute veloicty

• Speed and Velocity
• Speed and Direction
• Mass and acceleration 
• Speed and acceleration

Changing Velocity

• Velocity will change if either speed or direction changes.

• Constant speed and constant velocity are not the same.

Multiple Choice

What is the symbol is used for average velocity?

• $\overline{v}$

• $v_f$

• $v_o$

• $\Delta$

• Average velocity involves total displacement, instead of distance

• It is calculated by dividing the total displacement by the time interval.

Multiple Choice

Which formula is used to find average velocity?

• $\overline{v}=\frac{v_f-v_o}{2}$

• $\overline{v}=\frac{v_f+v_o}{2}$
  

• $\overline{v}=v_f+v_o$
  

• $\overline{v}=v_f+v_o$
  

Open Ended

Example: The position of a runner as a function of time is plotted as moving along the x-axis of a coordinate system. During a 3.00 s time interval, the runner’s position changes from x₁=50.0 m to x₂ = 30.5m. What was the runner's average velocity? (Remember, velocity is a vector)