Motion, Speed, Velocity, and Acceleration!

Motion

A change in position, over time, relative to a reference point.

So, What’s a Reference Point

Thumb/Wall ExampleCarwashDriving/Truck

What we compare all other movement or locations to!Often Earth FeaturesLarge Objects

Reference Point Scenarios

Suppose you are in a train, and you cannot tell if you are stopped or moving. Outside the window, another train is

slowly moving forward. What could be happening?

Your train is stopped, and the other train is moving slowly forward…

The other train is stopped, and your train is moving slowly backwards…

Both trains are moving forward, with the other train moving a little faster…

Your train is moving very slowly backward, and the other train is moving slowly forward…

Could you be sure as to which is actually happening??

Reference Point Examples

Speed

Position can change at different ratesDistance an object moves in an amount

of timeFormulas

Distance / Time

S=D÷T D=T·S T=D÷S

30mph; 15 cm/year; 500 m/s

Suppose there’s a TORNADO that’s 1 mile wide, and it’s going 40 mph…

What else is important?!?!?It’s Direction!

Velocity is a Speed in a Direction!15 Mph Northwest; 200 m/s South;

40 cm/ms Left

Velocity

Resultant Velocity

The sum of all of the velocities of an object! (How Fast The Object REALLY is Moving…)

BusRunner

Introductions:

Resultant Velocity

5 m/s East

What is the Runner’s Resultant Velocity??

(How fast is he REALLY moving??)

5 m/s East

What About Now??

5 m/s East

What is the Runner’s Resultant Velocity??

(How fast is he REALLY moving??)

2 m/s East

7 m/s East

What About Now???

1 m/s West

5 m/s East

What is the Runner’s Resultant Velocity??

(How fast is he REALLY moving??)

4 m/s East

What About Now??? (Last One)

5 m/s West

5 m/s East

What is the Runner’s Resultant Velocity??

(How fast is he REALLY moving??)

0 m/s

Acceleration

Change in Velocity over timeRemember: Velocity is Speed AND Direction“Speeding Up” = Acceleration (Positive #)“Slowing Down” = Deceleration (Negative #)

Turning (Change in Direction) = Acceleration

Study each car above CAREFULLY!

1. Which car(s) undergo an acceleration?

2. Which car experiences the greatest acceleration?

3. Which line from the position/time graph below corresponds to each car?

Calculating Acceleration

THIS IS TOUGH!!!

Final Velocity – Initial Velocity

Time

Vfinal– Vinitial

T

Vf – Vi

T

V

T

Acceleration Problem #1!

Mrs. Willever trips on a curb and starts sliding down a hill with a velocity of 1m/s south. After 3 seconds, her velocity is 7m/s south. What is

Mrs. Willever’s acceleration?

Final Velocity – Initial VelocityTime

7 m/s – 1 m/s3s

6 m/s3s

2 m/ss

2 m/s2

Acceleration Problem #2! You are walking down the street when you see an enormous, 112kg pickle

rolling towards you at 9 m/s. You are, of course, surprised by a pickle of this size, let alone the fact that it is rolling down the street. You jump in front of it and begin pushing on it until you finally bring it to a stop 45 seconds later. At this point you are arrested for interfering in the “World’s Largest Pickle Rolling Championships”. Determine the acceleration of the pickle.

Final Velocity – Initial VelocityTime

0 m/s – 9 m/s45 s

-9 m/s45 s

-1 m/s5 s

-1/5 (or -0.2) m/s2

Practice!

At the top of your notebook paper, please write the following formulas:

Speed/Distance/Time Formulas:

S=D÷T D=T·S T=D÷S

Acceleration Formula:

Final Velocity – Initial VelocityTime