http://glencoe.com/sec/science/physics/ppp_09/animation/Chapter%202/Position-Time%20Graphs.swf

Notes

Ideas

Ideas

Ideas

**What is motion?**

~~Fire Starter!~~

What do you already know?

Motion

Describing Speed: S=d/t

Who is faster Usain Bolt or a Cheetah?

Velocity:

V=d/t

The only difference between Speed

and Velocity is the

new component of

Direction.

Remember: motion is described as an object's change in position over time.

Question 1:

What do you know about speed?

Describe speed the best you can.

Question 2:

What about Velocity; tell me what you know about velocity.

QUESTION 3

Finally tell me about Acceleration.

The motion of an object is defined by its change of position over a period of time

Distance is

the length of the route you travel.

Displacement is

the change in position of the object or the distance between the starting and the ending point.

Bolt holds the world record in the 100 meter dash.

S=d/t

S=100m/9.58s

Bolt runs an average speed of 10.43 meters per second

The Cheetah holds the record for the fasts burst of speed for a mammal.

S=d/t

Sp.=100m/6.10s

The cheetah's average speed is 16.39 meters per seconds

Any combinations of units for distance and time can be used to describe speed.

Example: Kilometers per hour , centimeters

per day , meters per second, miles per hour

Note :

The metric system unit for speed is m/s.

m/s = meters/second

YAAAYYYY FINN and Jake are Back

MMMM BRAINS

Finn and Jake are being chased by a brain crazy zombie.

The zombie is able to run at 5m/s

AHHHHH

Zombie

If the zombie is able to run 5m/s, Finn and Jake must run at least 6 m/s.

How long must it take them to run a distance of 450m to escape the zombie?

To solve the problem:

Write the equation we are going to use.

S=d/t

Next input the numbers we know.

6m/s=450m/t

Solve the equation: t= 450m/6m/s

t=75s

There are two types of speed we can measure

Instantaneous Speed:

The speed of an object at any instant.

Average Speed:

The total distance traveled by an object divided by the

total time it took.

In this class we will use average speed:

S=(df-di)/t

Ex: We can see instantaneous speed anytime we are traveling in a car by looking at the speedometer. That is the speed we are moving in a vehicle at a given point in time.

Speed

is a

scalar quantity

. It has only

magnitude. It can be represented by a single number.

Velocity

is a

vector quantity.

It has both magnitude and direction. It can be represented by a number and an angle on a coordinate plane.

Increasing velocity is represented by a green arrow.

Decreasing velocity is represented by a blue arrow.

X) Two escalators next to each other going up and down. Each has a speed

of 2 km/h.

Because their direction is opposite, they have different Velocities.

1) If an object continues in the same direction, but

speeds up or slows

down,

it’s velocity has changed.

2) If an object continues at the same speed, but

changes direction

, its

velocity has changed.

Ways to Change Velocity:

Riddle

me

this

?

?

?

?

?

?

?

I can run as fast as possible for as long as I like.

I will never change speeds, but my velocity always changes. Why?

Because I am running around a track and my direction always changes.

A graph of distance vs time (or motion graph) is useful in describing and interpreting motion that is linear.

**Sp=d/t**

Do Now!

Distance VS. Displacement

Two examples of how to calculate speed when given the Distance and the time.

TRY TO FIND HOW FAR BOLT COULD RUN IN 60 SECONDS IF HE STAY AT THE SAME SPEED THE ENTIRE TIME.

STEP 1: WRITE THE EQUATION:

S=d/t

STEP TWO: FIND ALL GIVEN VARIABLES:

S=10.43m/s & t=60s

Step 3: What is the unknown:

d=distance

STEP 4: PUT VARIABLES INTO EQUATION:

10.43m/s= d/(60s)

STEP 5: SOLVE EQUATION:

625.8m

A scalar quantity is a quantity that just gives magnitude or how much of something.

ex: temperature, speed, how much something cost. Austin is 32 miles away.

A vector quantity is a something that not only tells us the how much part, but also tells me in what directions:

ex: velocity, Austin is 32 miles NORTH

**V=d/t**

What is motion?

How would you describe it?

Give an example of motion.

A person walks 5 km/h. The train is moving at 80 km/h with respect to the ground. How fast is the person going with respect to the ground?

Frame of Reference

FRAME OF REFERENCE

Any measurement of position, distance, or speed must be made with respect to a frame of reference.

You have gone a distance of 60 m, but your displacement is less than that! You could find it by using the Pythagorean Theorem. Where the displacement is equal to the hypotenuse.

10 m south

50 m east

Then you go 10 m south

Let’s say you go 50 m east.

Speed

distance traveled divided by the time it takes to travel that distance

Here is a video-song to help you remember this formula!

A point used to describe the location of something.

Time

Distance

DISTANCE-TIME GRAPHS

Time is always plotted on the X-axis (bottom of the graph). The further to the right on the axis, the longer the time from the start.

Plotting distance against time can tell you a lot about motion. Let's look at the axis:

Distance is plotted on the Y-axis (side of the graph). The higher up the graph, the further from the start.

On a motion graph...

A straight line indicates constant speed

A horizontal line indicates no motion or zero speed

Graphing Motion

A positive slope shows positive velocity

A negative slope shows negative velocity

A steeper slope = faster speed

Curved line = linear acceleration or a change in speed

Group Practice

Which runner stopped? How can you tell? For how long was the runner stopped? Explain your answers.

Summary…

A distance-time graph tells us how far an object has moved with time.

• The steeper the graph, the faster the motion.

• A horizontal line means the object is not changing its position - it is not moving, it is at rest.

• A downward sloping line means the object is returning to the start.

**A=V/t**

Acceleration : A=v/t

The rate at which the velocity of an object is changing

This is a measure of how the velocity of an object changes with respect to time.

Acceleration =change of velocity

time

The types of acceleration:

1) speeding up – positive acceleration

2) slowing down – negative acceleration

3) changing direction.

Acceleration = final speed - initial speed

time

Another way to think about acceleration is:

Practice with Acceleration!

X) Suppose a jet starts at rest at the end of a runway. As it takes off, it reaches a

speed of 80 m/s in 20 s.

(Straight down the runway, its speed and velocity are the same.)

Acceleration =

final speed - initial

time

What we know:

Vf=80m/s

vi=0m/s

t=20s

What we don't know:

ACCELERATION

PUT THEM IN THE EQUATION

A=vf-vi

t

A=80m/s-0m/s

20s

A= 80m/s

20s

Solve the equation

A=80m/s

20s

A=4m/s

Which of the graphs shows that one of the runners started 10 yards further ahead than the other? Explain.

In which of the graphs above are both of the runners running at the same speed? Explain.

Look at the graph below. It shows how three runners ran a 100-meter race. Which runner won the race? Explain your answer.

Do Now: Describe the motion in this graph.

A

B