Velocity + Acceleration

SI units

SI units needed Time = seconds (s) Other common units are the minute,

hour, microsecond and nanosecond Distance = meters (m) Other common units are the

centimeter, millimeter, kilometer, nanometer and picometer

Distance vs. Displacement

Distance is equal to the total amount of space something moved

Displacement is the space moved from the initial position.

Speed

Lunar recession = 1.3x10-9 Snail = 1x10-6 Man = 10m/s Cheetah = 30 m/s Sound at S.L. = 340 m/s M-16 bullet = 975m/s SR-71 Blackbird = 981m/s Apollo =11082 m/s *record Earth orbit = 29800 m/s Solar system orbit = 2x105

m/s Light = 3x108 m/s

Speed: Rate of change in position or how fast something is going

Given in distance per unit of time

m/s km/h mph In physics magnitude

of velocity vector Average speed – total

distance/ total time 95 miles in 1:20 What is

the average speed?

Instant speed

Instantaneous speed – speed at an exact moment in time – speedometer in a car

Constant speed – objects with no variation in speed – vehicles rarely travel at constant speeds

Velocity

Calculating speed: s = d/t

Velocity : speed and direction of something

V=d/t 2 people traveling at

60 km/h in different directions don’t have the same velocity

Thought Question: Does constant speed necessarily imply constant velocity?

Calcultions

You travel from Mandan to Fargo in your ‘87 Oldsmobuick, the trip of 210 miles takes you 2 hours 40 minutes. What was your average velocity.

How long would it take you to travel to Minneapolis 66O km if you drove at 115 km/h.

How far is the nearest star if it takes you 2.7 years traveling at the speed of light to reach it.

Problems

Speed and velocity are often used interchangeably but it is important to remember that velocity implies a direction of travel. This is especially important when it comes to the forces and energy that cause changes in motion.

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Graphing

http://webphysics.davidson.edu/physlet_resources/bu_semester1/c2_twocars_graphs.html

What do the slopes of each graph represent?

Acceleration

Acceleration is the change in velocity over time. Constant speed does not imply constant velocity

Positive acceleration- Acceleration in the same direction as velocity

Negative acceleration- acceleration in the opposite direction of velocity

Acceleration

How many ways can you accelerate in your car?

1. 2. 3. So your car has 3

accelerators Calculate acceleration

:

Acceleration formulas

To calculate acceleration Calculate the change in velocity and

divide by the change in time. a =( final velocity – initial velocity) /

time for the change to take place a= vf – vi/t or a = v /t

Acceleration Problem

If you drop a penny off of the Empire State Building and it reaches a speed of 29.4m/s after 3 seconds, what is its average acceleration?

How long would the penny have to fall to reach a speed of 100m/s?