Speed, Acceleration and Energy

Speed

• Speed= The distance an object travels in a specific amount of time.

• Speed= DistanceTime

• In S.I. units, Distance will always be measured in meters & Time will always be measured in seconds

• The units for speed are m/s.

The Magic Triangle• Cover up the variable you are trying to

find.

• Plug in the numbers you are given

• Solve for the unknown

D

S T

Divide

Multiply

Velocity and Constant Speed

• Velocity is speed AND direction

• Constant speed: speed is not increasing or decreasing, but stays the same over time.

Dist.

Time

Constant Speed

QuickTime™ and aTIFF (Uncompressed) decompressor

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The car is moving equal distances in equal amountsOf time. Thus, the speed is constant.

Acceleration

• Acceleration is any change in velocity.

• Acceleration=

Final Speed - Start Speed (∆ V)

Time

Acceleration Continued

• Positive Acceleration: When the speed of an object increases

Distance

Time

Positive Acceleration

QuickTime™ and aTIFF (Uncompressed) decompressor

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Acceleration Continued

• Negative Acceleration: The slowing down of an object over time. Also known as deceleration. The value will always be negative.

Distance

Time

Acceleration Problems

• When figuring out an acceleration problem the following steps should be followed:

• 1. Create a timeline to represent the problem.• 2. Find the start speed of the problem and

place on the first line of the timeline.• 3. For every change in speed a new line is

placed on the time line.• 4. Fill in the times• 5. Do the math

Acceleration Timeline

Start Speed

Speed Speed Speed FinalSpeed

Time Time Time Time

Each Section of the time line gets calculated separately

A=?? A=?? A=?? A=??

Speed Problems

• A cucumber walks along a dirty alley searching for his pet olive. If the cucumber walked the length of the alley in 75 seconds and the length of the alley was 4.6 m, what was the speed of the cucumber?

• Speed = Distance ÷ Time

= 4.6 m ÷ 75 s

= .0613 m/s

• A cute, little bunny chases a donkey down the street with a giant slingshot filled with pinecones. If the street is 22 m long and the donkey is running at a speed of 1.8 m/s, how long does it take for the donkey to get to the end of the street? If the bunny wants to get to the end of the street one second faster than the donkey, how fast must he run?

• Donkey’s Time = Distance ÷ Speed

= 22m ÷ 1.8 m/s

= 12.22 s

Bunny’s speed= Distance ÷ Time

= 22 m ÷ 11.22 s

= 1.96 m/s

• A lonely piece of corn-on-the cob rolls down a hill at a speed of 3.23 m/s. At the same time a little boy named, Claude Peppersmeller, throws his father’s glass eye down the hill. The glass eye travels at a speed of 1.095 m/s and takes 1 minute and 33 seconds to reach the bottom of the hill. What is the distance from the top of the hill to the bottom and how long did it take the corn to reach the bottom?

• Hill Distance= Speed of Eye x Time

= 1.095 m/s x 93 s

= 101.835 m

Time of Corn= Distance/Speed of corn

= 101. 835 m/ 3.23 m/s= 31. 527 seconds

Acceleration Problems• A large glass eye gets pushed from the top of a hill

down toward a river at the bottom. 8 seconds after it starts rolling it passes a small band of ants playing banjos and harmonicas. As it passes this band of “Hill Billy” ants it is traveling at a speed of 1.8 m/s. It continues to roll and 6 seconds later it passes a small Roley Poley bug playing solitare. The eye is traveling at a speed of 3.1 m/s at the time it passes the bug. 11 seconds later it finally comes to rest on the bottom of the river. What was the acceleration of the course of each stage of its trip?

Speed=0 m/s 1.8 m/s 3.1 m/s 0 m/s

T= 8 s T= 6 s T= 11 s

A= .225 m/s2 A= .287 m/s2 A= -.281 m/s2

`

Speed= 0 m/s 1.05 m/s .95 m/s 2.1 m/s 0

T=10 T=13 T=14

Can you make up a problem to go with this data?

T=7

A= 105 m/s2 -.014 m/s2 .088 m/s2 -.15 m/s2

Energy

• Energy is the ability to do work or create some type of change.

• Various types of energy exist (chemical, electrical, nuclear, etc.)

• Energy of Motion: energy that results from the movement or lack of movement of an object.

Energy of Motion

• Potential Energy: Known as energy of Position

• P.E. is energy stored in an object waiting to be used.

• P.E.= mass x height• Mass is always in kg and height always in

meters.• When an object is not moving it has potential

energy.

• Kinetic Energy: Energy of movement• K.E. exists when any object is in motion.• Potential energy is changed into K.E.

• Conservation of Energy: Energy is neither created or destroyed, it just changes forms.

The Magic Triangle…….Again!!

(Please stop, I’m sick of this stupid thing)

H

PE

M

• KE= mass of object x (speed of object)2

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»All energy is measured in units known as Joules (J)