Analysis questions3-4 SENTENCES EACH • How do you know work was done in this activity? • What is the difference between work and power? • How could you decrease the amount of work you did lifting the object? (Think about the factors that affect work) • How could you increase the amount of power you used? (Think about the factors that affect power)
Bellwork Quiz • What is power? • A. The amount of force you apply over a certain distance. • B. How much force is used when you do work. • C. The rate at which the work is done (how fast or slow you do it) • D. Another word for force.
How do Machines Help Us? • Homework Check • Bellwork Quiz • Review key concepts • Physics classroom examples (review) • Label input/output force on diagrams • Practice problems
Bellwork Quiz How do machines help us? • A. Machines change the amount of force you need to exert. • B. They change the distance over which you exert the force. • C. They change the direction of the force making it easier. • D. They change the AMOUNT of work done. • E. Answers a, b, and c.
Word problemsIdeally: Workin = Workout You pull a hammer backwards to take a nail out. Your arm goes down .5 meters and you use 10 N of force. The hammer pulls the nail .1 meters out of the wood. What is the resistance force of the hammer on the nail? 2. You push a carjack down with 50 N of force and it goes down .8m. The Jack pushes the car up .3 meters. What is the resistance force of the carjack On the car? 3. You open a can with a can opener using 8 N of force. Your hand moves A distance of 33cm. The resistance force is 12 N. How much distance did the Can opener make the lid move? 4. If the distance the machine is making the object move is LESS than the Distance YOU are moving, how is the machine being helpful?
5. You put 10N of force into a machine. The machine puts 20 N of force onto the object. Your arm moves .25 m when using this machine. What is the resistance distance? 6. Make 1 of your own problems solving for any 4 of the variables. 7. Get started on your homework : Reading C.
How MUCH do machines helps us? • Mechanical advantage practice problems. • Efficiency practice problems. • Make a book of MA for each simple machine. INCLUDE: • Name of simple machine • Equation for calculating the MA • Real life example for calculating the MA • Illustration of the MA for that simple machine
Bellwork Quiz • If a machine you used has a HIGH mechanical advantage it means: • A. You used MORE force when using the machine. • B. You used LESS force when using the machine. • C. The machine was very efficient. • D. The machine was not efficient at all.
What types of simple machines are there? • Online Lab
Bellwork Quiz An inclined plane helps you put a box in a truck by: • A. Increasing the force you exert to get the box into the truck. • B. Decreasing the distance you have to carry the box into the truck. • It decreases the amount of work done. • D. Decreasing the force you exert to get the box into the truck.
What other simple machines are there? • Online Lab
Bellwork Quiz • Which pulley would help you lift something the MOST?
Review • What 3 ways do machines make work easier? • What causes a machine to be less than 100% efficient? • Draw 3 simple machines and label the effort force and resistance force • Give examples of work being done and work not being done. • How is work different from power? • What does conservation of work mean? • Define the following: • Work • Power • Mechanical advantage • Efficiency
TERMS • work • power • mechanical advantage • efficiency • joule • watt • effort force • resistance force • effort distance • resistance distance CONCEPTS • 3 ways a simple machine makes work easier • Reason (s) why machines are not 100% efficient • Use the work equation to explain the COMMON THEMES among simple machines. (Meaning they all make work easier but HOW they make work easier is a common theme. What happens to the AMOUNT of work is a common theme too) • pulleys use more than one way to make work easier. • Fulcrum placement. (Where the fulcrum should be placed on a class I lever to use the LEAST amount of force. )
Critical Thinking Questions • What type of machine would be used to lower an empty bucket into a well and then lift the bucket full of water? Why? • Describe the relationship between friction and the efficiency of a machine. • To open a door, you push the part of the door that is farthest from the hinges. Why would it be harder to open the door if you pushed on the center of it? Explain. • A machine with 75% efficiency does 3300 Joules of work. Using the machine, how much work did you do?