Chapter 9 Section 3: Acceleration

Chapter 9 Section 3: Acceleration• Key concepts: What kind of motion does

acceleration refer to? How is acceleration calculated? What graphs can be used to analyze the motion of an accelerating object?

• Key term: acceleration

What is acceleration?

• Acceleration (OMG is that really how you spell that? Why does that look so funny right now…) is the rate at which velocity changes.

• Remember: velocity refers to speed AND direction of an object.

Acceleration: a change in velocity• In science, acceleration refers to increasing speed,

decreasing speed, or changing direction.

• Increasing speed = accelerates• Decreasing speed = deceleration (or negative

acceleration) • Changing direction: (even an object travelling at a

constant speed can be accelerating!!) a softball, for example, accelerates when it changes direction as it is hit; a runner as he/she rounds a curve accelerates even if maintaining a constant speed

How can a car be accelerating if it is maintaining constant speed?

Calculating acceleration

• To determine the acceleration of an object moving in a straight line, you must calculate the change in speed per unit of time.

• Acceleration = final speed – initial speedtime

Acceleration calculations continued• SI unit for acceleration is usually m/s2

• For example: imagine an adorable plane

The adorable plane

• The adorable plane accelerates as it takes off. Of course it does, otherwise we would never go anywhere and you would sit there on the tarmac asking your flight attendant for more tiny bags of peanuts for 8 hours and then you would get off the plane (or “deplane) in exactly the same place you started. Anyway…

It accelerates• How do we calculate its acceleration? • Please look at figure 7 on page 322 of your books

Do you remember the equation for acceleration?

• At first, the plane is not moving. So its initial speed is 0 m/s

• Its final speed is 40m/s• It takes 5 seconds

• So, to calculate the average acceleration of the plane, you subtract the initial speed of 0 m/s (it isn’t moving when it starts) from the final speed of 40m/s, then divide the change in speed by the time, 5 seconds. Your answer is 8 m/s2

In your notes

• Please attempt both math practice problems on page 323. Remember acceleration’s formula

• Acceleration = final speed – initial speedtime

How to graph acceleration

• You can use both a speed vs time graph and a distance vs time graph to analyze the motion of an acceleration object

• Look at the graph in figure 8• How can you calculate the acceleration from

this graph? Easy: calculate the slope of the line• Rise/run = slope

What else can you tell from the graph?

• This is important: you will need to know how to read graphs for the rest of your ever-lovin’ lives!

• B/c the line is straight: the acceleration was constant

• b/c the line goes up: speed was increasing

Distance vs time graph figure 9 pg 325

• A curved line means that the object is accelerating b/c you travelled a greater distance each second than the second before it

We’re done wid dis chaptahh

• Now we commits it to memoriess