Lesson 6: Acceleration

Lesson 6: Acceleration

How Changes in Velocity Are Calculated and Communicated

​Acceleration

Acceleration is a measure of the change in velocity during a period of time. It typically uses similar units as speed, but is:

​distance/time²

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​So, acceleration is usually seen as:

​Two Ways Velocity Changes...

​Velocity is the direction and speed of an object. So, if either the direction or the speed of the object changes, then the velocity has changed. This means that if an object turns, speeds up, slows down, stops, or does a 180 turn, then it is accelerating, or changing velocity.

​Acceleration Formula

​First, you find the new speed of the object, then you subtract the starting speed of the object from its final speed. Then, you divide by however many seconds, minutes, or hours it was accelerating. Most are written using meters and seconds.

​Practice Problems:

1) Janet stands at the starting line of a track and takes off running. She reaches 4 miles per hour after 2 seconds. What was her acceleration?​

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​2) A Ferrari can go from 0 mph to 60 mph in 2.4 seconds. What is its acceleration?

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​3) My dog goes from running 10 mph to a complete stop in 5 seconds after sliding across the hardwood floor. What was his acceleration?

Multiple Choice

A garbage truck reaches 45 mph 9 seconds after being completely stopped. What was its acceleration?

• $$5\ \frac{mi}{hr^2}$$  

• $$9\ \frac{mi}{hr^2}$$  

• $$45\ \frac{mi}{hr^2}$$  

• $$18\ \frac{mi}{hr^2}$$  

​Speed/Time Graphs

​In a speed/time graph, we can see how the object accelerates, decelerates, and cruises at a constant speed. Any flat areas (such as the blue section of the curve) show the object is maintaining constant speed. The areas which slope upward show that it is speeding up and the areas where it slopes downward shows it is slowing down.

NOTE:​

Speed/Time graphs do not show the direction of the object, so it is possible the object is accelerating even though the speed/time graph is flat due to a change in direction even though its speed is constant.​

Multiple Choice

A car takes a curve going 45 mph the entire time. Is it accelerating?

• Yes, it is accelerating.

• No, it is not accelerating.

Multiple Choice

A dog runs in circles around a table. Is he accelerating?

• Yes, he is accelerating.

• No, he is not accelerating.