1 speed and velocity what is speed, velocity and acceleration? how does speed, velocity and...

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Speed and VelocitySpeed and Velocity

What is speed, velocity and acceleration?

How does speed, velocity and acceleration relate to Forces & Motion?

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How does MOTION relate to POSITION and TIME?How does MOTION relate to POSITION and TIME?

MOTION often includes speed and is a change in position.

QUESTION: Do you have to see something move to know that motion has taken place?

ANSWER: No – because the only thing needed is a reference point to see that something has changed position.

SPEED then is the rate of change in position or the “rate of motion.”

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Pretend you are looking at your car's speedometer while you are driving. The reading you get from

your speedometer is…

This is the speed that you are traveling at that moment.

instantaneous speed.

Measures of Speed

http://rds.yahoo.com/S=96062883/K=speedometer/v=2/TID=DFI2_21/l=IVI/*-http://www.carcrazy.net/images/home/picture.gif

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Now, let’s say you are on a highway, a car may travel at the same speed for a long period of time this would be…

constant speed.

This is the speed that does not vary – cruise control.

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Now, let’s say that you are trying to determine the distance you are going to traveled in a given amount of time– this

would be…

average speed.

- - - - - - - - - - -

KatyHouston

Speed is the distance traveled per unit of time.

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Distance, Speed and Time is shown in the equation:

Calculating Speed

s =d

t

...or shortened:

s = Speed d = Distance t = Time

speed =distance

time

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Manipulating the Equation

Dmeters

Sm/s

Tseconds

multiply

divide

So, to find DISTANCE, we need to MULTIPLY speed and time.

d = s x t

The equation reads - but it can be rearranged to solve for any variable.

s =d

t

And, to find TIME, we need to DIVIDE distance by the speed.

t =d

s

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FIVE Step Approach to Solving Problems

(G )Step 1 Read the problem. Write down the GIVENS

(U) Step 2 Write down the UNKNOWNS. What you are looking

for?????

(S) Step 4 SUBSTITUTE the numbers.

(E) Step 3 Write down the EQUATION.

(S) Step 5 SOLUTION. Box Answer with UNITS!

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“A car traveled 110 miles in 2 hours.”

Consider the problem…

d =t =s =

Formula Substitute Answer

Units, units, units!

Step 1 Read the problem.Write down the GIVENS.

110 miles2 hours

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d =t =s =



110 miles2 hours


110 miles2 hours

Step 2 Write down the UNKNOWNS.What are you trying to find?

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d =t =s =



110 miles2 hours

Step 3 Write down the EQUATION.

s =d

t

s =d

t

12


d =t =s =



110 mi2 hours

Step 4 Substitute the numbers.Step 5 SOLUTION. Box Answer with Units.

55mi/hr

dt

S = 110 mi2 hr

S = 55 mi/hrS =

2 hours

110 miles

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Do the problems 1-3 on your

notes.

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“A runner’s average speed during the 10 kilometer race was 20 km/hr. What was his time?’”

Consider the problem…

d =t =s =



Step 1 Read the problem. Write down the GIVENS.

10 kmSpeed of runner:

20 km/hr

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d =

t =s =



10 km

20 km/hr

Step 2 Write down the UNKNOWNS. What are you trying to find?

10 kmSpeed of runner:

20 km/hr


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Step 3 Set up the EQUATION.


d =

t =s =

10 km

20 km/hrt = ds

10 km

Speed of runner: 20 km/hr

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Step 4 SUBSTITUTE the numbers.Step 5 SOLUTION. Box Answer with Units.

d =

t =s =

10 km

20 km/hr

0.5 hr


0.5 hr

If the runner’s average speed was 20 km/hr during the 10km race, the runner’s time was 0.5 hours.

dt = s

t = 10 km

20 km/hr

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notes.

19“You decide to go to Dallas to visit your friends. Your friends tell you that it takes 4 hours to get to Dallas at an average speed of 70 miles per hour. Approximately how many miles is it to their house?”Step 1 Read the problem.

Write down the GIVENS.

Step 2 Write down the UNKNOWN.

What are you trying to find?

Step 4 SUBSTITUTE the numbers.Step 5 SOLUTION. Box Answer

with units.




d =

t =s =

280 mi

70 mi/hr

4 hr

?

If I drive 4 hours at 40mph, the distance from Houston to Dallas is 280 miles.

d = s x t d = 70mi/hr x 4 hr d = 280 miles

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Do problem 6 on your notes.

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Rate of Swimmers

0

400

800

1200

1600

2000

2400

0 5 10 15 20 25 30

Time in minutes

Dis

tanc

e in

met

ers

A distance/time graph makes it possible to “see” speed.This graph shows how fast the swimmers went during their workout.

Which swimmer swam at a constant (the same) speed throughout her workout?

Which one stopped during his/her workout?

Consta

nt spee

d

Stopped here

400 meters at 10, 15, & 20 minutes

Is a

str

aight l

ine

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Make the speed graph in your notes & answer the questions.

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(Reading on your speedometer)

Average speed-is over time

Instantaneous speed-

at that moment

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What is the difference between speed and

velocity?

55 mi/hr

55 mi/h

r

55 mi/hrAll of these cars had the same SPEED but, different VELOCITIES

because they were traveling in different directions.

Velocity has speed & direction.

If you change direction, you have changed your velocity – and if you have changed your speed,

you have changed your velocity. Therefore, any change in speed OR direction is a

change in velocity!

Speed is how fast

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Why is it important to know the

VELOCITY of a tornado?

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Acceleration … is defined as the change in velocity over time.

final velocity – initial velocity

timeacceleration =

Vf - Vi

ta =

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Types of Acceleration

• Positive Acceleration– Velocity and acceleration are in the

same direction.– Object SPEEDS up.

•Negative Acceleration–Velocity and acceleration are in opposite direction.–Object SLOWS down.

28 A go-cart started from the top of a hill at 5 meters per second. At the bottom of the hill it ended up with a speed of 35 meters per second 6 seconds later. What was the acceleration of the go-cart?

Step 1 Read the problem. Write down the GIVENS.

top

bottom35 m/s

5 m/s

In 6 sVf =

Vi=

t =

a =


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top

bottom35 m/s

5 m/s

6 sVf =

Vi=

t =

a =


Step 2 Write down the UNKNOWNS.

What are you trying to find?

35 m/s

5 m/s

6 s

Finish:final

Velocity

Start:initial

Velocity

A go-cart started from the top of a hill at 5 meters per second. At the bottom of the hill it ended up with a speed of 35 meters per second 6 seconds later. What was the acceleration of the go-cart?

30

top

bottom35 m/s

5 m/s

6 sVf =

Vi=

t =

a =

35 m/s

5 m/s

6 s

Final Velocity

InitialVelocity




Vf - Vi

t

Vf - Vi

t

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Vf =

Vi=

t =

a =

35 m/s

5 m/s

6 s


Vf - Vi

t

35m/s – 5 m/s

6s

30 m/s

6 s= 5

m/s2

Step 4 SUBSTITUTE the numbers.Step 5 SOLUTION. Box Answer with Units.

5 m/s2


The go-cart that traveled from 5m/s to 35 m/s in 6 seconds had an acceleration of 5m/s2.

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notes.

1 speed and velocity what is speed, velocity and acceleration? how does speed, velocity and...

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