Motion NotesSpeed, Velocity, and Acceleration!

Motion

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

So, What’s a Reference Point?

http://www.classzone.com/books/ml_science_share/vis_sim/mfm05_pg7_relmotion/mfm05_pg7_relmotion.html

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

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

Speed=Distance/TimeDistance=Speed x TimeTime= Distance/speed

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

Acceleration

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

Which of the Following Are Examples of Acceleration?

A car stops at a stop light.A car goes from 0 to 45

mph.A car races around an oval

track at a constant speed.

Acceleration Formula

THIS IS TOUGH!!!

Final Velocity – Initial Velocity

Time

Vfinal– Vinitial

T

Acceleration Problem!Julio starts sliding with a velocity of 1m/s south. After 3 seconds, his

velocity is 7m/s south. What is Julio’s acceleration?

Final Velocity – Initial VelocityTime

7 m/s – 1 m/s3s

6 m/s3s

2 m/ss

2 m/s2

Practice!

Review:

Speed/Distance/Time Formulas:

S=D÷T D=T·S T=D÷S

Acceleration Formula:

Final Velocity – Initial VelocityTime

Practice

If a runner runs 100 meters in 50 seconds, what is his speed in meters per second?

How far could this runner run in 25 seconds?

Calculating Acceleration

John starts running from rest. After 10 s, his velocity is 20 m/s. What is John’s rate of acceleration?