8.6B: SPEED, VELOCITY, AND ACCELERATION

Goal: be able to identify & know the difference between the 3 of

these

Review of 8.6A

Balanced forces = no change of movement Object might not move Object move at a constant speed (think outer

space) Unbalanced forces = movement

The object will move in the direction of the larger force

Think football or tug of war

Review

Net Force Overall forces on an object

Same direction arrows = add

Different direction arrows = subtract

Review

Speed Triangle Distance always goes on top

Be able to solve for all 3 variables

8.6B Speed

Speed: the distance we travel divided by the time it takes to get there

Speed can be expressed in many ways: Meters/second Inches/year Km/hr Cm/decade

All of the above have the distance on top and unit of time on the bottom

What is velocity?

Velocity and speed are very similar.

Velocity is defined as: speed with direction

For velocity, you still use the speed equationBUT:You now have to include which direction the object is going

Examples of Velocity

24 miles /hr North 3 mm / second East 10 km / year Up

Notice how all of the above are speed, except they also include the direction. That’s velocity.

Velocity

Write the following in your notes. Write the letter: S if the example is speed or V if the example is velocity.

1. 60 miles per hour2. 4 inches per year East3. 12 cm per day West4. 2 meters per second

Why velocity matters?

Example: airline pilot

Speed: we only know how fast the pilot is going

Velocity: we know how fast AND we know WHERE the pilot is going

Acceleration

Acceleration is defined as the rate of change in velocity. Unit: meters per second squared (m/s2)

AKA: speeding up, slowing down, or changing direction.

MYTH: to accelerate means to go faster

TRUTH: to accelerate means you are just changing your speed OR direction

Different Accelerations

Positive Acceleration: speeding up Math: positive slope Math: positive number

Uphill graph

Negative Acceleration: slowing down Math: negative slope Math: negative number

Downhill graph

Tricky Language

Constant acceleration and constant velocity are NOT the same.

If an object’s velocity changes, the object is accelerating.

If an object’s velocity does not change, it does not accelerate, no matter how fast it is moving.

Acceleration is the RATE of change.

Graphs & Rates

Graphs are used to show the relationship between 2 variables.

Graphs are used in all jobs and careers.

Graphs can show trends, or patterns, between the two variables.

Understanding the Axis

Speed = distance OR: y (rise)time x (run)

What this means on a speed or velocity graph:

Distance will be your y axisTime will be your x axis

Understanding the Axis

How does acceleration look on a graph? Same idea.

Unit for acceleration: m/s2

Velocity is also meters per secondTime time (s)

Velocity is the y axis; time is on the x axis