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Work & Speed

Work & Speed. Work. YOURS:. TEXTBOOK:. Work is the transfer of energy to an object by using a force that causes the object to move in the direction of the force.

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Work & Speed

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  1. Work & Speed

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

  3. Work or Not Work? OR OR YES NO YES NO

  4. Force YOURS: TEXTBOOK: A push or a pull exerted on an object in order to change the motion of the object; force has size and direction. Examples: people, bulldozer, static electricity

  5. Work or Not Work? • Problem #1: • Fabian carries a backpack from the cafeteria to the 8th grade hallway. • Problem #2: • Alexis applies force to (pushes) a cart.

  6. Work or Not Work? • Problem #3: • Kayla pushes a stack of books across the floor. • Problem #4: • Andrew wears a backpack and climbs up the side of a mountain.

  7. We have learned that forces can change both the direction and speed of an object. • For example…

  8. To determine SPEED: Average Speed = Distance Time

  9. To determine TIME: Time = Distance Speed

  10. To determine DISTANCE: Distance = Speed x Time

  11. Units of Measurement • Speed=miles per hour or meters per second • Distance=meters, miles, kilometers… • Force=newtons • Work=joules or newton-meters

  12. How long does it take to travel: • 120 miles at 40 mph • 60 miles at 40 mph • 390 miles at 60 mph • Calculate the distance that you would travel if you drove for: 1. 3 hours at 20 mph 2. 10 hours at 60 mph 3. 5 hours at 45 mph

  13. Practice Problem #1: --Daniela drives a car 100 miles (m) in 2 hours (h). Using the formula for speed, determine Daniela’s average speed during that time.

  14. Practice Problem #2: --Klelian jogs to her house 72 meters (m) away in a time of 36 seconds (s). What is Klelian’s average speed?

  15. Practice Problem #3: --If you travel 7 kilometers (km) and walk for 1 hour (h), what is your average speed?

  16. Practice Problem #4: --An airplane traveling from Atlanta to Las Vegas travels 1,260 km in 3 h. What is the airplane’s average speed?

  17. Practice Problem #5: • Tammie cycles 20 miles per hour on her bike for 4 hours. How far does Tammie cycle in this time?

  18. Final Practice Problem…. • If you rode your bike 2 hours and traveled 24 miles, what is your rate of speed?

  19. Example #1: --On vacation to Florida, Alexia’s family traveled 300 miles at 30 mph. How long did the trip take?

  20. Example #2: --Cristian drove his truck from Nashville to Chicago at a rate of 30 miles per hour. How far could Cristian drive in 3 hours?

  21. Example #3: --Daniel drove his red Dodge Charger at an average speed of 100 kilometers per hour for 10 hours on a country road. How far did Daniel travel?

  22. Test Bonus Question: • A snail moves at a distance of 8 meters in 2 hours. Calculate the average speed of the snail.

  23. To leave class… • Which of these statements is true about a moving object that increases its speed? • The object’s mass increased. • The object is not accelerating. • A force is acting on the object. • No forces are acting on the object.

  24. The equation for WORK is… Work = Force x Distance or W = F x D

  25. Work Problem #1: --Kammi uses a lever to lift a large stone from the ground. Kammi applies a force of 50 newtons and moves the stone 5 meters. How much work is being done by Kammi?

  26. Work Problem #2: --Mariah wants to move a stack of magazines from one room of her house to another. Using a wheel and axle, Mariah applies a force of 100 newtons and moves the stack 10 meters. How much work is being done by Mariah?

  27. The equation for FORCE is… Force = Work ________ Distance or F = W ______ D

  28. Force problem #1: --Ashley performed 100 joules of work by moving a pile of rocks 10 meters with a lever. What was the force on the rocks?

  29. Force Problem #2: -Cameron performed 500 joules of work by lifting a car 50 meters with a pulley. What was the force on the car?

  30. VELOCITY • The measure of an object’s SPEED and DIRECTION Example: 1. a person walks 5 m/h east 2. a bird flies 10 km/h north

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

  32. Velocity changes if: 1. Speed changes OR 2. Direction changes For example: a bus traveling at 15 m/s south speeds up to 20 m/s south

  33. Acceleration • The rate at which velocity changes (either speed or direction)

  34. Which of the following is NOT an example of acceleration? A. a person jogging at 3 m/s along a winding path B. a car stopping at a stop sign C. a cheetah running 27 m/s east D. a plane taking off

  35. Problem Examples: 1. Create 5 VELOCITY examples *****For example: a person travels 5 mph north) 2. Create 5 speed word problems *****For example: A student travels 10 miles for 1 hour. What is their average speed?

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