Acceleration

Acceleration The rate* at which an object’s velocity changes *rate = a change over time

Three types of Acceleration Positive acceleration Increase in velocity Speeding up Negative acceleration Decrease in velocity Slowing down AKA deceleration Change in direction with or without velocity change

Is there acceleration? Discuss with a neighbor whether it is describing acceleration or not You are riding your bike at 9 km/hr. Ten minutes later, your speed is 6 km/hr You ride your bike around the block at a constant speed of 11 km/hr You ride your bike in a straight line at a constant speed of 10 km/hr You are stopped at a red light and then it turns green

Doing the math 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) (also written as Vf – Vi)

What’s the unit? 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 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/s 4s = 40 m/s 3s = 30 m/s

Some words to look out for Zero words Words that either mean the objects starts at rest (not in motion) or stops its motion Stop At rest At a standstill

Let’s calculate 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? Write what is given: Vi = 0 m/s (it started at rest) Vf = 80 m/s ∆t = 20 s Solve for acceleration:

Let’s calculate…again 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? Write what is given: Vi = 3 m/s Vf = 0 m/s (came to a stop) ∆t = 2 s Solve for acceleration:

Warm up 9/3 (write the prompt then answer) Write the following numbers/units and label as either: distance, time, mass, speed or velocity 34 mi/hr 29 g 125 m 89 hr 24.5 m/sec west