Acceleration

Define velocity

Give an example

(If you have not done so – hand in your lab)

Warm- up

Motion can be in:◦A straight line◦Circle/curved path◦Back and forth motion

Uniform motion◦The simplest kind of motion◦Along a straight line◦Feels smooth◦No change in velocity

A recap of Motion

Un-uniform motion◦Along a curved or up and down path◦Feels bumpy Ex: roller coasters, stop and go traffic, walk/jog/walk

◦Change in velocityThis is acceleration!! The rate* at which an object’s velocity changes*rate = a change over time

What if motion is not constant?

Positive acceleration◦Increase in velocity◦Speeding up

Negative acceleration◦Decrease in velocity◦Slowing down

Change in direction◦with or without velocity change

Three types of Acceleration

Number 1 -3 on your white board and write yes or no next to each number to answer whether it is describing acceleration or not

1. You are riding your bike at 9 km/hr. Ten minutes later, your speed is 6 km/hr

2. You ride your bike around the block at a constant speed of 11 km/hr

3. You ride your bike in a straight line at a constant speed of 10 km/hr

4. You are stopped at a red light and then it turns green

Is there velocity?

To find acceleration:A = ∆V ∆ t∆ is the greek letter delta and means “the change in”◦To find the change in velocity: final velocity of the object (Vf) minus initial

velocity of the object (Vi)◦To find the change in time: final time of the object’s motion (tf) minus

initial time of the object (ti)

Doing the math

Acceleration is a unit of speed divided by a unit of time◦ Ex: m/s/s

Can also be written as m/s2

◦ Ex: km/hr/s◦ Ex: km/hr/hr

Can also be written as km/hr2

What does this unit mean?◦ It tells you how much velocity is changing per unit

of time Ex: 5 m/s2

Means that velocity is increasing (because it’s a positive #) by 5 m/s every second that the object travels

What’s the unit?

What does it mean?–Ex 2: if a car is accelerating at a rate of 10 m/s/s then its velocity is increasing by 10 m/s every second it is traveling

1s = 10 m/s

2s = 20 m/s3s = 30 m/s4s = 40 m/s

Zero words◦Words that either mean the objects starts at rest (not in motion) or stops its motion

◦Stop◦At rest◦At a standstill

Some words to look out for

A jet starts at rest at the end of a runway and reaches a speed of 80 m/s in 20s. What is its acceleration?

1. Write what is given:◦ Vi = 0 m/s (it started at rest)

◦ Vf = 80 m/s◦ ∆t = 20 s

2. Solve for acceleration:

Let’s calculate

A skateboarder is moving in a straight line at a speed of 3 m/s and comes to a stop in 2 seconds. What is his acceleration?

1. Write what is given:◦ Vi = 3 m/s

◦ Vf = 0 m/s (came to a stop)◦ ∆t = 2 s

2. Solve for acceleration:

Let’s calculate…again