Work & Speed

Work & Work & SpeedSpeed

YOURS:YOURS: TEXTBOOK:TEXTBOOK:

Work is the transfer of energy Work is the transfer of energy to an object by using a force to an object by using a force that causes the object to that causes the object to move in the direction of the move in the direction of the force.force.Work is done on an object if Work is done on an object if two things happen: 1) the two things happen: 1) the object moves as a force is object moves as a force is applied, 2) the direction of the applied, 2) the direction of the object’s motion is the same object’s motion is the same as the direction of the force.as the direction of the force.Examples: pushing a ball up a Examples: pushing a ball up a hillhill

OROR ORORYES NO YES NO

YOURS:YOURS: TEXTBOOK:TEXTBOOK:

A push or a pull A push or a pull exerted on an object in exerted on an object in order to change the order to change the motion of the object; motion of the object; force has size and force has size and direction.direction.

Examples: people, Examples: people, bulldozer, static bulldozer, static electricityelectricity

Work or Not Work?Work or Not Work?Problem #1:Problem #1:

–Fabian carries a backpack from Fabian carries a backpack from the cafeteria to the 8the cafeteria to the 8thth grade grade hallway. hallway.

Problem #2:Problem #2:

–Alexis applies force to (pushes) a Alexis applies force to (pushes) a cart.cart.

Work or Not Work?Work or Not Work?Problem #3:Problem #3:

–Kayla pushes a stack of books Kayla pushes a stack of books across the floor. across the floor.

Problem #4:Problem #4:

–Andrew wears a backpack and Andrew wears a backpack and climbs up the side of a mountain.climbs up the side of a mountain.

We have learned that We have learned that forces can change both forces can change both the direction and speed the direction and speed of an object.of an object.

–For example…For example…

To determine To determine SPEEDSPEED::

Average Speed = DistanceAverage Speed = Distance

TimeTime

To determine To determine TIMETIME::

Time = Time = DistanceDistance

SpeedSpeed

To determine To determine DISTANCEDISTANCE::

Distance = Speed x TimeDistance = Speed x Time

Units of MeasurementUnits of Measurement

Speed=miles per hour or meters per Speed=miles per hour or meters per secondsecond

Distance=meters, miles, kilometers…Distance=meters, miles, kilometers…

Force=newtonsForce=newtons

Work=joules or newton-metersWork=joules or newton-meters

How long does it take to travel: How long does it take to travel:

a.a. 120 miles at 40 mph120 miles at 40 mph

b.b. 60 miles at 40 mph60 miles at 40 mph

c.c. 390 miles at 60 mph390 miles at 60 mph

Calculate the distance that you would travel Calculate the distance that you would travel if you drove for:if you drove for:

1. 3 hours at 20 mph1. 3 hours at 20 mph



Practice Problem #1:Practice Problem #1:--Daniela drives a car 100 miles (m) --Daniela drives a car 100 miles (m)

in 2 hours (h). Using the formula for in 2 hours (h). Using the formula for speed, determine Daniela’s speed, determine Daniela’s average speed during that time. average speed during that time.

Practice Problem #2:Practice Problem #2:

--Klelian jogs to her house 72 meters --Klelian jogs to her house 72 meters (m) away in a time of 36 seconds (m) away in a time of 36 seconds (s). What is Klelian’s average (s). What is Klelian’s average speed?speed?


--If you travel 7 kilometers (km) and --If you travel 7 kilometers (km) and walk for 1 hour (h), what is your walk for 1 hour (h), what is your average speed?average speed?


--An airplane traveling from Atlanta to --An airplane traveling from Atlanta to Las Vegas travels 1,260 km in 3 h. Las Vegas travels 1,260 km in 3 h. What is the airplane’s average What is the airplane’s average speed?speed?


Tammie cycles 20 miles per hour Tammie cycles 20 miles per hour on her bike for 4 hours. How far on her bike for 4 hours. How far does Tammie cycle in this time?does Tammie cycle in this time?

Final Practice Problem….Final Practice Problem….

If you rode your bike 2 hours and If you rode your bike 2 hours and traveled 24 miles, what is your rate traveled 24 miles, what is your rate of speed? of speed?

Example #1:Example #1:

--On vacation to Florida, Alexia’s --On vacation to Florida, Alexia’s family traveled 300 miles at 30 family traveled 300 miles at 30 mph. How long did the trip take?mph. How long did the trip take?


--Cristian drove his truck from --Cristian drove his truck from Nashville to Chicago at a rate of 30 Nashville to Chicago at a rate of 30 miles per hour. How far could miles per hour. How far could Cristian drive in 3 hours?Cristian drive in 3 hours?


--Daniel drove his red Dodge --Daniel drove his red Dodge Charger at an average speed of Charger at an average speed of 100 kilometers per hour for 10 100 kilometers per hour for 10 hours on a country road. How far hours on a country road. How far did Daniel travel?did Daniel travel?

Test Bonus Question:Test Bonus Question:

A snail moves at a distance of 8 A snail moves at a distance of 8 meters in 2 hours. Calculate the meters in 2 hours. Calculate the average speed of the snail. average speed of the snail.

To leave class…To leave class…

Which of these statements is true about Which of these statements is true about a moving object that increases its a moving object that increases its speed?speed?

A.A. The object’s mass increased.The object’s mass increased.

B.B. The object is not accelerating.The object is not accelerating.

C.C. A force is acting on the object.A force is acting on the object.

D.D. No forces are acting on the object. No forces are acting on the object.

The equation for WORK is…The equation for WORK is…

Work = Force x DistanceWork = Force x Distance

oror

W = F x DW = F x D

Work Problem #1:Work Problem #1:

--Kammi uses a lever to lift a large --Kammi uses a lever to lift a large stone from the ground. Kammi stone from the ground. Kammi applies a force of 50 newtons and applies a force of 50 newtons and moves the stone 5 meters. How moves the stone 5 meters. How much work is being done by much work is being done by Kammi?Kammi?

Work Problem #2:Work Problem #2:

--Mariah wants to move a stack of --Mariah wants to move a stack of magazines from one room of her magazines from one room of her house to another. Using a wheel house to another. Using a wheel and axle, Mariah applies a force of and axle, Mariah applies a force of 100 newtons and moves the stack 100 newtons and moves the stack 10 meters. How much work is being 10 meters. How much work is being done by Mariah?done by Mariah?

The equation for FORCE is…The equation for FORCE is…

Force = Force = WorkWork________________DistanceDistance

oror

F = F = WW____________

DD

Force problem #1:Force problem #1:

--Ashley performed 100 joules of --Ashley performed 100 joules of work by moving a pile of rocks 10 work by moving a pile of rocks 10 meters with a lever. What was the meters with a lever. What was the force on the rocks?force on the rocks?

Force Problem #2:Force Problem #2:

-Cameron performed 500 joules of -Cameron performed 500 joules of work by lifting a car 50 meters with work by lifting a car 50 meters with a pulley. What was the force on the a pulley. What was the force on the car?car?

VELOCITYVELOCITY

The measure of an object’s The measure of an object’s SPEED and DIRECTIONSPEED and DIRECTION

Example: 1. a person walks 5 m/h eastExample: 1. a person walks 5 m/h east

2. a bird flies 10 km/h north2. a bird flies 10 km/h north

Think…Think…

Imagine that two birds leave the Imagine that two birds leave the same tree at the same time. same tree at the same time. They both fly at 10 km/h for 5 They both fly at 10 km/h for 5 min, 12 km/h for 8 min, and 5 min, 12 km/h for 8 min, and 5 km/h for 10 min. Why don’t they km/h for 10 min. Why don’t they end up at the same place?end up at the same place?

Velocity changes if:Velocity changes if:

1. Speed changes1. Speed changesOROR

2. Direction changes2. Direction changes

For example: a bus traveling at 15 For example: a bus traveling at 15 m/s south speeds up to 20 m/s m/s south speeds up to 20 m/s

southsouth

AccelerationAcceleration

The rate at which velocity The rate at which velocity changes (either speed or changes (either speed or

direction)direction)

Which of the following is NOT Which of the following is NOT an example of acceleration?an example of acceleration?

A. a person jogging at 3 m/s along a A. a person jogging at 3 m/s along a winding pathwinding path

B. a car stopping at a stop signB. a car stopping at a stop sign

C. a cheetah running 27 m/s east C. a cheetah running 27 m/s east

D. a plane taking offD. a plane taking off

Problem Examples:Problem Examples:

1. Create 5 VELOCITY examples1. Create 5 VELOCITY examples*****For example: a person travels 5 mph *****For example: a person travels 5 mph north)north)

2. Create 5 speed word problems2. Create 5 speed word problems

*****For example: A student travels *****For example: A student travels 10 10 miles for 1 hour. What is their miles for 1 hour. What is their

average speed?average speed?

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Work & Speed